# The Clinical Value of 3D Ultrasonic Measurement of the Ratio of Gestational Sac Volume to Embryo Volume in IoT-Based Prediction of Pregnancy Outcome

Authors: Yong Wang; Tiantian Li; Lichun Zhang; Jing Li; Bo Zou; Bhupesh Kumar Singh
Journal: Journal of Healthcare Engineering
 (2021)

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## Abstract

The objective of the research study is to investigate the use of three-dimensional ultrasonic measurement technology, to determine the size of gestational sac and embryo volume, and to use the ratio of gestational sac volume to embryo volume in IoT-based prediction of pregnancy outcome. The abnormal and normal pregnancy identifiers are there, which assists in prediction of pregnancy outcomes: whether the pregnancy is normal or may suffer pregnancy loss during first trimester. For the observational study, 500 singleton pregnant women who made an appointment for delivery in Qiqihar Hospital from January 2015 to June 2019 were considered. The 500 pregnant women received transvaginal ultrasound at 6+0 ∼ 8+0 weeks of gestational age to measure gestational sac volume (GSV), yolk sac volume (YSV), and germ volume (GV). According to pregnancy outcome, they were divided into fine group (n = 435) and abortion group (n = 65). Among the 500 cases, 435 had normal delivery and 65 had abortions. According to the results of gestational age (GA) analysis, the pregnancy success rates at 6 (n = 268), 7 (n = 184), and 8 weeks (n = 48) were 85.8%, 87.5%, and 91.7%, respectively. Comparison of pregnancy failure rate among the three groups shows statistically significant difference. The morphology of germ, yolk sac, and gestational sac cannot be used as a predictor of pregnancy outcome in various degrees. The results of multivariate Cox proportional regression analysis show the following: the ratio of germ volume (GV) to gestational sac volume (GSV) (P=0.008) has an impact on the prediction of spontaneous abortion prognosis, showing statistically significant difference; yolk sac volume (YSV), germ volume (GV), and gestational sac volume (GSV) have no effect on the prediction of spontaneous abortion prognosis (P>0.05). The ratio of GSV to germ volume has a strong prognostic value for pregnancy results. To a certain extent, the ratio of gestational sac volume to germ volume can predict spontaneous pregnancy abortion at 6th week of gestation, providing a theoretical basis for clinical ultrasound pregnancy examination indicators.


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## Body

## 1. Introduction

The accurate distinction between regular pregnancy and abnormal pregnancy in the first trimester is a quite challenging problem for clinical investigations. It is projected that about 30–40% of implantation pregnancies result in impulsive termination of pregnancy in the first trimester [1]. Pregnancy outcome can be predicted based on transvaginal ultrasound imaging [2] (TVS) and biochemical markers like β-HCG (human chorionic gonadotropin) [3], PAPP-A (pregnancy-associated plasma protein-A) [4], unbounded estriol [5], and alpha-fetoprotein (AFP-plasma protein of foetus) [6]. The early predictions of disease help doctors to make early decisions to save the life of patients. Internet of things (IoT) is working as a catalyst to enhance the power of AI applications in healthcare [7, 8]. The patients who require regular attention can be monitored by the doctors remotely using the IoT sensors deployed on their bodies or surroundings [9, 10]. These biological markers can provide directions for screening of unambiguous cases of aneuploidy. Usually, TVS method is used for testing all the pregnancies. The ultrasound based markers are examined to recognize pregnancies intended to be lost. The good resolution images can certainly assist in the diagnosis of intrauterine pregnancy loss. The yolk sac (YS) is also considered as biomarker for study of pregnancy loss. YS is the very first recognizable structure which can be observed through ultrasound. Specifically, YS bigger than 6.0 mm is associated with pregnancy loss. In general, the growth of YS from the very first appearance up to 10 weeks shows pregnancy growth outlines and also assists in the prognosis of pregnancy loss. Ultrasound testing of GS, YS diameter, crown rump length (CRL), and thickening of the endometrium are used to envisage the pregnancy results. However, even if these indicators are checked to be normal, more than 10% of pregnant women experience abortions [11]. In the first three months, gestational sac is the primary source of exchange between the foetus and the mother before the foundation of the placental circulation, which has hematopoietic, metabolism, secretion, excretion, and immunogenic functions. The primary GS is formed at about 24 days of gestational age (calculated from the first day of the last menstrual period). As the additional embryonic coelom is formed, the main GS is squeezed, and secondary GS is formed after 28 days of gestational age, which is the first embryo structure envisioned in the gestational sac on ultrasound. In a normal pregnancy, the yolk sac (YS) can be detected in the fifth week of pregnancy. Usually, the YS appears as a round structure with an anechoic centre surrounded by a uniform thick and distinct echo wall. The size of the yolk sac from the 5th week to the 10th week of pregnancy is usually taken to judge whether the pregnancy is normal. Figure 1 shows various abnormal ultrasound findings of yolk sac.Figure 1
Various abnormal ultrasound findings of YS. (a) Lack of YS; (b) large YS; (c) small YS; (d) echo YS; (e) calcified YS; (f) irregular YS.
(a)(b)(c)(d)(e)(f)


### 1.1. Contributions of the Research Work

(1)
The sample size of 500 singleton pregnant women who received production inspection and also made an appointment for delivery in the hospital was considered for research study.(2)
After ignoring structural abnormalities of the uterus and cervix, the transvaginal ultrasound (TVS) on an empty bladder was completed on the Voluson S6 pro ultrasound device with a 5–9 MHz multifrequency transvaginal transducer. Then, an appropriately sized 3D sampling frame was placed on the part of the gestational sac to collect three-dimensional images of the gestational sac.(3)
The data in this study were processed by using the statistical analysis tool SPSS 20.0.(4)
Measurement data are expressed by “mean ± standard deviation” (±s); one-way analysis of variance is used for comparison between groups; LSD-t test is used for pairwise comparison between groups. One-way analysis of variance is used for comparison between multiple groups. Logistic regression is used to calculate the regression equation and to analyse the relationship between parameter values like pregnant women condition, gestational sac, germ, and abortion factors.(5)
The pregnancy outcomes were divided according to gestational age and correlations between germ, yolk sac, and pregnancy sac morphology with pregnancy outcome were analysed.


### 1.2. Related Work

Many research studies are presented by the doctors and researchers which reveal the significance of ultrasounds and aligned techniques for the diagnosis of pregnancy results. A few studies are mentioned below.The size and shape of germs are considered as subtle forecasters of pregnancy outcomes, but recent researches have shown that the TVS testing is also contradictory in certain cases [12, 13]. Therefore, it is necessary to further study the germ size and its relationship with normal as well as abnormal pregnancy outcome, so that germ can be taken up as indicator in an early prognosis of pregnancy results. In [14], 360 women with positive pregnancy were taken up for study with threatened miscarriage at a tertiary hospital unit in Singapore. The outcome measured the spontaneous miscarriage. Statistical parameters such as the ROC curve, sensitivity, and specificity score were considered. The limit value for serum progesterone validated clinical significance and allows the physicians to segregate the patients into high- and moderate-risk groups for impulsive miscarriage. In [15], for observational study, pregnant women with 42 to 76 days of pregnancies were enrolled. 800 women got early spontaneous termination in their pregnancies. The study concludes that ultrasound measurements can reveal the signs of early abortion.In [16], 2601 pregnant women with cardiac activity were observed after IVF. TVS was performed for GA within 6–10 weeks. 201 women faced miscarriage during the first three months after it was observed from foetus cardiac activity. The study concludes that logistic model is significant for predicting pregnancy outcomes through foetus cardiac activity. In [17], binary logistic regression was utilized for ascertaining whether serum AMH levels played any role in the occurrence of a miscarriage or other independent factors were also involved for miscarriage such as ovarian response, age, and other confounding factors. In [18], the YS has been testified as a responsible forecaster of adversative pregnancy outcomes. YS diameters were obtained with 2D ultrasound gestations from 5 to 11 weeks. 193 patients were taken up for observatory perspective. It was diagnosed that all pregnant women with large YS got miscarriage within 10 weeks, and women with smaller YS got miscarriage after the 10 weeks.Mature theory has not yet formed regarding parameters of GSV and germ volume in the first trimester. Although there are similar literatures, the sample size is small and the research perspectives are different. In this study, three-dimensional ultrasonic measurement technology was used to measure the parameters of gestation sac and germ volume in the first trimester, aiming to investigate the value of the ratio of gestational sac to germ volume in predicting pregnancy outcome.The paper is arranged into 4 sections. The next section provides information on the methods and materials. The third section elaborates pregnancy results and analysis. Finally conclusion is presented.


## 1.1. Contributions of the Research Work

(1)
The sample size of 500 singleton pregnant women who received production inspection and also made an appointment for delivery in the hospital was considered for research study.(2)
After ignoring structural abnormalities of the uterus and cervix, the transvaginal ultrasound (TVS) on an empty bladder was completed on the Voluson S6 pro ultrasound device with a 5–9 MHz multifrequency transvaginal transducer. Then, an appropriately sized 3D sampling frame was placed on the part of the gestational sac to collect three-dimensional images of the gestational sac.(3)
The data in this study were processed by using the statistical analysis tool SPSS 20.0.(4)
Measurement data are expressed by “mean ± standard deviation” (±s); one-way analysis of variance is used for comparison between groups; LSD-t test is used for pairwise comparison between groups. One-way analysis of variance is used for comparison between multiple groups. Logistic regression is used to calculate the regression equation and to analyse the relationship between parameter values like pregnant women condition, gestational sac, germ, and abortion factors.(5)
The pregnancy outcomes were divided according to gestational age and correlations between germ, yolk sac, and pregnancy sac morphology with pregnancy outcome were analysed.


## 1.2. Related Work

Many research studies are presented by the doctors and researchers which reveal the significance of ultrasounds and aligned techniques for the diagnosis of pregnancy results. A few studies are mentioned below.The size and shape of germs are considered as subtle forecasters of pregnancy outcomes, but recent researches have shown that the TVS testing is also contradictory in certain cases [12, 13]. Therefore, it is necessary to further study the germ size and its relationship with normal as well as abnormal pregnancy outcome, so that germ can be taken up as indicator in an early prognosis of pregnancy results. In [14], 360 women with positive pregnancy were taken up for study with threatened miscarriage at a tertiary hospital unit in Singapore. The outcome measured the spontaneous miscarriage. Statistical parameters such as the ROC curve, sensitivity, and specificity score were considered. The limit value for serum progesterone validated clinical significance and allows the physicians to segregate the patients into high- and moderate-risk groups for impulsive miscarriage. In [15], for observational study, pregnant women with 42 to 76 days of pregnancies were enrolled. 800 women got early spontaneous termination in their pregnancies. The study concludes that ultrasound measurements can reveal the signs of early abortion.In [16], 2601 pregnant women with cardiac activity were observed after IVF. TVS was performed for GA within 6–10 weeks. 201 women faced miscarriage during the first three months after it was observed from foetus cardiac activity. The study concludes that logistic model is significant for predicting pregnancy outcomes through foetus cardiac activity. In [17], binary logistic regression was utilized for ascertaining whether serum AMH levels played any role in the occurrence of a miscarriage or other independent factors were also involved for miscarriage such as ovarian response, age, and other confounding factors. In [18], the YS has been testified as a responsible forecaster of adversative pregnancy outcomes. YS diameters were obtained with 2D ultrasound gestations from 5 to 11 weeks. 193 patients were taken up for observatory perspective. It was diagnosed that all pregnant women with large YS got miscarriage within 10 weeks, and women with smaller YS got miscarriage after the 10 weeks.Mature theory has not yet formed regarding parameters of GSV and germ volume in the first trimester. Although there are similar literatures, the sample size is small and the research perspectives are different. In this study, three-dimensional ultrasonic measurement technology was used to measure the parameters of gestation sac and germ volume in the first trimester, aiming to investigate the value of the ratio of gestational sac to germ volume in predicting pregnancy outcome.The paper is arranged into 4 sections. The next section provides information on the methods and materials. The third section elaborates pregnancy results and analysis. Finally conclusion is presented.


## 2. Information and Methods

### 2.1. General Information

In the observational study presented in this paper, 500 singleton pregnant women who received production inspection and made an appointment for delivery in our hospital from January 2015 to June 2019 were selected as the study subjects. After obtaining the approval of the ethics committee and the institutional review committee, the 500 pregnant women received transvaginal ultrasound at 6+0∼8+0 weeks of gestational age to measure GSV and germ volume (GV). According to pregnancy outcome, they were segregated into fine pregnancy group (n = 435) and abortion or termination group (n = 65). The follow-ups were taken till the end of the pregnancy.


### 2.2. Method

After excluding structural abnormalities of the uterus and cervix, hypothyroidism, obvious diabetes, and multiple pregnancy cases, according to the patient’s informed written consent, ultrasound (TVS) was performed on empty bladder using Voluson S6 pro ultrasound device with a 5–9 MHz frequency, showing minimal intra- and interobserver variations. Then, an appropriately sized three-dimensional sampling frame was placed on the part of the gestational sac to collect three-dimensional images of the gestational sac. The GSD (gestational sac diameter) is the aggregation of the three vertical diameters measured from one inner edge of the trophoblast to the other inner edge. Germ diameter (YSD) depicts the aggregation of two vertical diameters, where the caliper is located on the internal edge of the YS (yolk sac). By using computer image processing technology to rotate or move theX-axis, Y-axis, and Z-axis planes in parallel, the optimal visual effect and clarity can be acquired. By using the automatic volume measurement mode, the volumes of GSD, YS, and germ can be calculated one by one.


### 2.3. Statistical Processing

The data collected for the research study are analysed using statistical tool known as SPSS 20.0. The data are expressed by “mean ± standard deviation” (x¯±s), one-way analysis of variance or repeated measurement analysis of variance is used for comparison between groups, LSD-t test is used for pairwise comparison between groups, and one-way analysis of variance is used for comparison between multiple groups. Logistic regression is used to calculate the regression equation and analyse the relationship between parameter values like pregnant women condition, gestational sac, germ, and abortion factors, and comparison between groups is performed by χ2 analysis; P<0.05 means statistically significant difference.


## 2.1. General Information

In the observational study presented in this paper, 500 singleton pregnant women who received production inspection and made an appointment for delivery in our hospital from January 2015 to June 2019 were selected as the study subjects. After obtaining the approval of the ethics committee and the institutional review committee, the 500 pregnant women received transvaginal ultrasound at 6+0∼8+0 weeks of gestational age to measure GSV and germ volume (GV). According to pregnancy outcome, they were segregated into fine pregnancy group (n = 435) and abortion or termination group (n = 65). The follow-ups were taken till the end of the pregnancy.


## 2.2. Method

After excluding structural abnormalities of the uterus and cervix, hypothyroidism, obvious diabetes, and multiple pregnancy cases, according to the patient’s informed written consent, ultrasound (TVS) was performed on empty bladder using Voluson S6 pro ultrasound device with a 5–9 MHz frequency, showing minimal intra- and interobserver variations. Then, an appropriately sized three-dimensional sampling frame was placed on the part of the gestational sac to collect three-dimensional images of the gestational sac. The GSD (gestational sac diameter) is the aggregation of the three vertical diameters measured from one inner edge of the trophoblast to the other inner edge. Germ diameter (YSD) depicts the aggregation of two vertical diameters, where the caliper is located on the internal edge of the YS (yolk sac). By using computer image processing technology to rotate or move theX-axis, Y-axis, and Z-axis planes in parallel, the optimal visual effect and clarity can be acquired. By using the automatic volume measurement mode, the volumes of GSD, YS, and germ can be calculated one by one.


## 2.3. Statistical Processing

The data collected for the research study are analysed using statistical tool known as SPSS 20.0. The data are expressed by “mean ± standard deviation” (x¯±s), one-way analysis of variance or repeated measurement analysis of variance is used for comparison between groups, LSD-t test is used for pairwise comparison between groups, and one-way analysis of variance is used for comparison between multiple groups. Logistic regression is used to calculate the regression equation and analyse the relationship between parameter values like pregnant women condition, gestational sac, germ, and abortion factors, and comparison between groups is performed by χ2 analysis; P<0.05 means statistically significant difference.


## 3. Results and Analysis

### 3.1. General Information of the Pregnant Women at Enrolment and Three-Dimensional Ultrasonic Measurement Results of Gestational Sac and Germ at 6+0∼8+0 Weeks of Gestational Age

Among the 500 cases (340 cases were first pregnancy and 196 cases were multiple pregnancies), 31 cases (6.2%) had a history of abortion. As the pregnancy progressed, 65 cases of pregnancy failure occurred, accounting for 13.0%. The gestational week is determined according to the germ’s crown rump length. The three-dimensional ultrasonic measurement results of the gestational sac and germ at each gestational week (6+0∼8+6) are shown in Table 1.Table 1
Three-dimensional ultrasound observation results.
Gestational weekCrown rump length (mm)Gestational sacGermAverage diameter (mm)Average diameter (mm)6+03.312.1 ± 0.78.5 ± 0.46+14.012.9 ± 0.49.1 ± 0.36+24.613.7 ± 1.19.8 ± 0.76+35.514.6 ± 1.310.5 ± 0.66+46.215.5 ± 1.211.2 ± 0.86+56.816.3 ± 0.911.8 ± 0.16+67.517.2 ± 1.612.5 ± 0.37+08.518.1 ± 1.113.3 ± 0.67+19.219.0 ± 0.913.7 ± 0.47+210.120.0 ± 1.714.2 ± 0.37+311.020.9 ± 1.414.6 ± 0.87+412.121.8 ± 0.915.1 ± 0.87+513.222.7 ± 1.215.6 ± 1.17+614.123.7 ± 1.416.1 ± 0.98+015.224.6 ± 1.816.6 ± 1.2


### 3.2. Dividing Pregnancy Outcomes according to Gestational Age

According to the analysis results of gestational age (GA), the pregnancy success rates at 6+0∼6+6 (n = 268), 7+0∼7+6 (n = 184), and 8+0∼8+6 (n = 48) weeks of pregnancy are 85.8%, 87.5%, and 91.7%, respectively. 38 pregnancy abortions received three-dimensional ultrasonic measurement at 6+0–6+6 gestational weeks in early pregnancy, with pregnancy failure rate of 14.2%. 23 pregnancy abortions received three-dimensional ultrasonic measurement at 7+0–7+6 gestational weeks, with pregnancy failure rate of 12.5%. When the pregnancy approaches 8+0–8+6 weeks, the figure is reduced to 4 (8.3%). In comparison of pregnancy failure rates between the three groups, the difference is statistically significant, with results shown in Table 2.Table 2
Dividing pregnancy outcomes according to gestational age.
Gestational weekNormal pregnancy (%)Pregnancy abortion (%)Total (%)Pregnancy failure rate (%)6+0–6+6230 (52.9)38 (58.4)268 (53.6)14.27+0–7+6160 (36.8)23 (35.4)184 (36.8)12.58+0–8+644 (10.1)4 (6.2)48 (9.6)8.3Total435 (100)65 (100.0)500 (100.0)13.0In this study, 14 out of 65 pregnancy abortion patients (21.5%) had a previous abortion. It is understood that, among the 29 women with a history of pregnancy abortion, 6 (20.7%) also had a pregnancy abortion during the current pregnancy.


### 3.3. Correlation between Germ, Yolk Sac, and Pregnancy Sac Morphology and Pregnancy Outcome

The presence of fetal germ when pregnant women receive the first three-dimensional ultrasonic scan is significantly correlated with pregnancy outcome (P<0.001). In the first scan, there are 431 cases with fetal germ and normal birth. The outcome is fine, with test sensitivity of 99.9%. However, there are 9.2% specific cases with lack of fetal germ and abortion, indicating whether there is any germ in the early pregnancy which can be used as an index to predict the pregnancy outcome to a certain extent, but there is certain prediction error. There are 403 cases with normal yolk sac shape and normal birth, with test result sensitivity of 92.6%, while there are 24.6% specific cases with abnormal yolk sac shape and abortion, indicating that regularity of yolk sac shape cannot be used as an indicator to predict the pregnancy outcome. There are 340 cases with regular gestational sac shape and normal delivery. The outcome is poor, with test sensitivity merely at 78.2%. In the meantime, there are 40% specific cases with irregular gestational sac shape and abortion, indicating that regularity of gestational sac shape cannot be used as an indicator to predict the pregnancy outcome. The results are shown in Table 3.Table 3
Correlation between the morphology of germ, yolk sac, and gestational sac and pregnancy outcome.
CharacteristicResultNormal delivery (%)Pregnancy abortion (%)χ2P valueGermNormal431 (99.9)6 (9.2)70.605—Missing4 (0.1)59 (90.8)<0.001Yolk sacNormal shape403 (92.6)16 (24.6)48.143—Abnormal shape32 (0.0)49 (75.4)<0.01Gestational sacRegular340 (78.2)26 (40.0)1.934—Irregular95 (21.8)39 (60.0)0.06


### 3.4. The Relationship between Gestational Sac, Yolk Sac, and Germ Parameters and Pregnancy Outcome

The shape and morphological factors of germ, yolk sac, and gestational sac cannot be used as predictors for pregnancy outcome in various degrees. Based on changes in average diameter of gestational sac and average diameter of embryo from 6+0 week to 8+0 week of gestation as well as different abortion rates during the period, it is considered that volume of germ and gestational sac (the calculation process of gestational sac volume is shown in Figure 2) may have a certain close relationship with pregnancy outcome.Figure 2
Three-dimensional image of the gestational sac at gestational age of 9+0–9+6. The area within the envelope is the three sections A, B, and C of the gestational sac and the final volume section D.
(a)(b)(c)(d)Starting from 6+0–6+6 gestational weeks, germ volume (GV), GSV, and YS volume (YSV) all increase with the increasing gestational week. At 6+0∼8+6 gestational weeks, there is a statistically noteworthy difference in GSV between any two adjacent weeks, P<0.05; statistically significant difference exists in GV between two adjacent weeks of 6+0∼8+6 gestational weeks, P<0.05. YSV shows no statistically noteworthy difference between two adjacent gestational weeks in 6+0∼8+6 gestational weeks, P>0.05. The results are shown in Table 4.Table 4
The mean and standard deviation of each volume parameter in 6+0∼8+6 gestational weeks (x ± s).
Gestational ageGSV (cm3)GV (cm3)YSV (cm3)6+0–6+611.14 ± 4.05∗0.73 ± 0.42∗0.15 ± 0.087+0–7+621.93 ± 9.241.57 ± 0.590.17 ± 0.148+0–8+635.92 ± 11.21∗3.28 ± 1.11∗0.18 ± 0.11Note. ∗P<0.05: compared with 7+0–7+6.GSV : GV gradually decreases from 22.06 at 6+0–6+6 gestational weeks to 12.11 at 8+0–8+6 gestational weeks as the gestational age increases. There is an extremely significant correlation between the ratio of gestational sac volume to germ volume and pregnancy abortion rate (P<0.01). The results are shown in Table 5.Table 5
Ratio of pregnancy sac volume to germ volume.
Gestational ageMeanStandard deviationRangePregnancy failure rate (%)6+0–6+622.0624.3311.36∼72.4614.27+0–7+615.027.484.65∼34.4512.58+0–8+612.113.786.19∼24.558.3In analysis of the influence of germ volume (GV), gestational sac volume (GSV), and yolk sac volume (YSV) on prediction of spontaneous abortion prognosis, the results of multifactor Cox proportional regression analysis indicate the following: the ratio of germ volume (GV) to gestational sac volume (GSV) (P=0.008) has an effect on the prediction of spontaneous abortion prognosis, showing statistically significant difference; germ volume (GV), gestational sac volume (GSV), and yolk sac volume (YSV) have no effect on the prediction of spontaneous abortion prognosis (P>0.05). The results are displayed in Table 6.Table 6
Proportion analysis of Cox, a predictor of pregnancy outcome.
ParameterBSEWaldP valueRR95.0% CILower limitUpper limitGV0.7190.3315.5920.0682.0340.8791.438GSV0.5610.3216.0210.0721.9980.9212.786YSV0.7320.9925.8980.1212.0310.4343.125GSV:GV1.0030.5616.4320.00012.8320.52315.124


## 3.1. General Information of the Pregnant Women at Enrolment and Three-Dimensional Ultrasonic Measurement Results of Gestational Sac and Germ at 6+0∼8+0 Weeks of Gestational Age

Among the 500 cases (340 cases were first pregnancy and 196 cases were multiple pregnancies), 31 cases (6.2%) had a history of abortion. As the pregnancy progressed, 65 cases of pregnancy failure occurred, accounting for 13.0%. The gestational week is determined according to the germ’s crown rump length. The three-dimensional ultrasonic measurement results of the gestational sac and germ at each gestational week (6+0∼8+6) are shown in Table 1.Table 1
Three-dimensional ultrasound observation results.
Gestational weekCrown rump length (mm)Gestational sacGermAverage diameter (mm)Average diameter (mm)6+03.312.1 ± 0.78.5 ± 0.46+14.012.9 ± 0.49.1 ± 0.36+24.613.7 ± 1.19.8 ± 0.76+35.514.6 ± 1.310.5 ± 0.66+46.215.5 ± 1.211.2 ± 0.86+56.816.3 ± 0.911.8 ± 0.16+67.517.2 ± 1.612.5 ± 0.37+08.518.1 ± 1.113.3 ± 0.67+19.219.0 ± 0.913.7 ± 0.47+210.120.0 ± 1.714.2 ± 0.37+311.020.9 ± 1.414.6 ± 0.87+412.121.8 ± 0.915.1 ± 0.87+513.222.7 ± 1.215.6 ± 1.17+614.123.7 ± 1.416.1 ± 0.98+015.224.6 ± 1.816.6 ± 1.2


## 3.2. Dividing Pregnancy Outcomes according to Gestational Age

According to the analysis results of gestational age (GA), the pregnancy success rates at 6+0∼6+6 (n = 268), 7+0∼7+6 (n = 184), and 8+0∼8+6 (n = 48) weeks of pregnancy are 85.8%, 87.5%, and 91.7%, respectively. 38 pregnancy abortions received three-dimensional ultrasonic measurement at 6+0–6+6 gestational weeks in early pregnancy, with pregnancy failure rate of 14.2%. 23 pregnancy abortions received three-dimensional ultrasonic measurement at 7+0–7+6 gestational weeks, with pregnancy failure rate of 12.5%. When the pregnancy approaches 8+0–8+6 weeks, the figure is reduced to 4 (8.3%). In comparison of pregnancy failure rates between the three groups, the difference is statistically significant, with results shown in Table 2.Table 2
Dividing pregnancy outcomes according to gestational age.
Gestational weekNormal pregnancy (%)Pregnancy abortion (%)Total (%)Pregnancy failure rate (%)6+0–6+6230 (52.9)38 (58.4)268 (53.6)14.27+0–7+6160 (36.8)23 (35.4)184 (36.8)12.58+0–8+644 (10.1)4 (6.2)48 (9.6)8.3Total435 (100)65 (100.0)500 (100.0)13.0In this study, 14 out of 65 pregnancy abortion patients (21.5%) had a previous abortion. It is understood that, among the 29 women with a history of pregnancy abortion, 6 (20.7%) also had a pregnancy abortion during the current pregnancy.


## 3.3. Correlation between Germ, Yolk Sac, and Pregnancy Sac Morphology and Pregnancy Outcome

The presence of fetal germ when pregnant women receive the first three-dimensional ultrasonic scan is significantly correlated with pregnancy outcome (P<0.001). In the first scan, there are 431 cases with fetal germ and normal birth. The outcome is fine, with test sensitivity of 99.9%. However, there are 9.2% specific cases with lack of fetal germ and abortion, indicating whether there is any germ in the early pregnancy which can be used as an index to predict the pregnancy outcome to a certain extent, but there is certain prediction error. There are 403 cases with normal yolk sac shape and normal birth, with test result sensitivity of 92.6%, while there are 24.6% specific cases with abnormal yolk sac shape and abortion, indicating that regularity of yolk sac shape cannot be used as an indicator to predict the pregnancy outcome. There are 340 cases with regular gestational sac shape and normal delivery. The outcome is poor, with test sensitivity merely at 78.2%. In the meantime, there are 40% specific cases with irregular gestational sac shape and abortion, indicating that regularity of gestational sac shape cannot be used as an indicator to predict the pregnancy outcome. The results are shown in Table 3.Table 3
Correlation between the morphology of germ, yolk sac, and gestational sac and pregnancy outcome.
CharacteristicResultNormal delivery (%)Pregnancy abortion (%)χ2P valueGermNormal431 (99.9)6 (9.2)70.605—Missing4 (0.1)59 (90.8)<0.001Yolk sacNormal shape403 (92.6)16 (24.6)48.143—Abnormal shape32 (0.0)49 (75.4)<0.01Gestational sacRegular340 (78.2)26 (40.0)1.934—Irregular95 (21.8)39 (60.0)0.06


## 3.4. The Relationship between Gestational Sac, Yolk Sac, and Germ Parameters and Pregnancy Outcome

The shape and morphological factors of germ, yolk sac, and gestational sac cannot be used as predictors for pregnancy outcome in various degrees. Based on changes in average diameter of gestational sac and average diameter of embryo from 6+0 week to 8+0 week of gestation as well as different abortion rates during the period, it is considered that volume of germ and gestational sac (the calculation process of gestational sac volume is shown in Figure 2) may have a certain close relationship with pregnancy outcome.Figure 2
Three-dimensional image of the gestational sac at gestational age of 9+0–9+6. The area within the envelope is the three sections A, B, and C of the gestational sac and the final volume section D.
(a)(b)(c)(d)Starting from 6+0–6+6 gestational weeks, germ volume (GV), GSV, and YS volume (YSV) all increase with the increasing gestational week. At 6+0∼8+6 gestational weeks, there is a statistically noteworthy difference in GSV between any two adjacent weeks, P<0.05; statistically significant difference exists in GV between two adjacent weeks of 6+0∼8+6 gestational weeks, P<0.05. YSV shows no statistically noteworthy difference between two adjacent gestational weeks in 6+0∼8+6 gestational weeks, P>0.05. The results are shown in Table 4.Table 4
The mean and standard deviation of each volume parameter in 6+0∼8+6 gestational weeks (x ± s).
Gestational ageGSV (cm3)GV (cm3)YSV (cm3)6+0–6+611.14 ± 4.05∗0.73 ± 0.42∗0.15 ± 0.087+0–7+621.93 ± 9.241.57 ± 0.590.17 ± 0.148+0–8+635.92 ± 11.21∗3.28 ± 1.11∗0.18 ± 0.11Note. ∗P<0.05: compared with 7+0–7+6.GSV : GV gradually decreases from 22.06 at 6+0–6+6 gestational weeks to 12.11 at 8+0–8+6 gestational weeks as the gestational age increases. There is an extremely significant correlation between the ratio of gestational sac volume to germ volume and pregnancy abortion rate (P<0.01). The results are shown in Table 5.Table 5
Ratio of pregnancy sac volume to germ volume.
Gestational ageMeanStandard deviationRangePregnancy failure rate (%)6+0–6+622.0624.3311.36∼72.4614.27+0–7+615.027.484.65∼34.4512.58+0–8+612.113.786.19∼24.558.3In analysis of the influence of germ volume (GV), gestational sac volume (GSV), and yolk sac volume (YSV) on prediction of spontaneous abortion prognosis, the results of multifactor Cox proportional regression analysis indicate the following: the ratio of germ volume (GV) to gestational sac volume (GSV) (P=0.008) has an effect on the prediction of spontaneous abortion prognosis, showing statistically significant difference; germ volume (GV), gestational sac volume (GSV), and yolk sac volume (YSV) have no effect on the prediction of spontaneous abortion prognosis (P>0.05). The results are displayed in Table 6.Table 6
Proportion analysis of Cox, a predictor of pregnancy outcome.
ParameterBSEWaldP valueRR95.0% CILower limitUpper limitGV0.7190.3315.5920.0682.0340.8791.438GSV0.5610.3216.0210.0721.9980.9212.786YSV0.7320.9925.8980.1212.0310.4343.125GSV:GV1.0030.5616.4320.00012.8320.52315.124


## 4. Discussion

Due to the irregular shape of gestational sac in the initial trimester, it is difficult to acquire accurate gestational sac volume parameters through conventional two-dimensional ultrasound. Three-dimensional ultrasound can make up for the inaccuracy of conventional two-dimensional ultrasound in estimation of GSV in the initial trimester, making it more scientific, quantitative, and repeatable. After implantation of the fertilized egg, the decidua changes rapidly in the endometrium, and the aponeurosis covers the fertilized egg. The fertilized egg is surrounded by the uterine muscle and the endometrium, forming a closed cavity, which is gestational sac. Ultrasound indicates that the gestational sac is filled with fluid, mainly villi, representing the chorionic cavity. As the gestational age increases, the gestational sac expands to about 10 and 11 cycles, and then the chorionic cavity begins to disappear, and the amniotic membrane and villi gradually disappear. Membrane is fused and replaced by the amniotic sac. After the embryo is implanted, the yolk sac separates from the original intestine and gradually degenerates, becoming a small capsule with a diameter of <5 mm which remains on the placenta surface. The extraembryonic mesoderm on the yolk sac forms many blood islands in the third week, which is the first part of the embryo to form blood vessels and blood cells. Also, it is the hematopoietic site of the early embryo. The yolk sac and vein will participate in the formation of mesenteric artery and hepatic portal vein. Since primordial germ cells first appear in the yolk sac wall, the yolk sac is the original source of germ cells. One week after fertilization, the embryo is implanted, which then grows into a foetus through cell division and cell differentiation. At the end of the third month, each organ system is basically established. Therefore, germ volume is continuously increased during pregnancy.In routine inspections, inspection of pregnancy sac, yolk sac, and germ constitutes the basic operation of production inspection. Relevant studies have shown that fetal chromosomal abnormalities are the main factors affecting the gestational sac shape. Chromosomal abnormalities can lead to termination of gestational sac development and thereby pregnancy abortion [14]. Germs can usually be found in embryos at 6th week of gestation, appearing at 8th week of gestation at the latest [15]. Yolk sac can usually be observed between the 5th and 6th weeks of gestation, which is displayed as a small halo structure in the gestational sac in three-dimensional ultrasound images.Of the 500 clinically diagnosed pregnant women who were enrolled in this study (340 were first pregnancy and 196 were multiple pregnancies), 31 cases (6.2%) had a history of abortion. As the pregnancy progressed, 65 cases of pregnancy failure occurred, accounting for 13.0%. This study analysed their gestational sac, yolk sac, and germ biomeasurements. In [18], the authors studied the relationship between yolk sac shape and pregnancy outcome in pregnant women and found that yolk sac shape was significantly different in pregnancy outcomes. In [11], the authors believed that yolk sac abnormality could lead to embryo death. However, the study presented in [19] believed that too large yolk sac was unrelated to adverse pregnancy outcomes, while too small yolk sac was related to spontaneous abortion. According to research, in the first scan, there are 431 cases with fetal germ and normal birth. The outcome is fine, with test sensitivity of 99.9%. However, there are 9.2% specific cases with lack of fetal germ and abortion, indicating whether there is any germ in the early pregnancy which can be used as an index to predict the pregnancy outcome to a certain extent, but there is certain prediction error. There are 403 cases with normal yolk sac shape and normal birth, with test result sensitivity of 92.6%, while there are 24.6% specific cases with abnormal yolk sac shape and abortion, indicating that regularity of yolk sac shape cannot be used as an indicator to predict the pregnancy outcome. There are 340 cases with regular gestational sac shape and normal delivery. The outcome is poor, with test sensitivity of merely 78.2%. In the meantime, there are 40% specific cases with irregular gestational sac shape and abortion, indicating that regularity of gestational sac shape cannot be used as an indicator to predict the pregnancy outcome.According to the study presented in [20], at less than 10 weeks of pregnancy, no YSD of pregnancy is greater than 5.6 mm in normal outcome. In [21], the authors found that YSD allows prediction of abnormal pregnancy outcomes within 2 standard deviations of the mean during pregnancy. The irregular YS shape allows the forecasting of adverse outcomes.


## 5. Conclusion

To conclude, it is difficult to form more accurate unified understanding of the prediction of pregnancy outcome. In this study, GSV:GV shows a stronger correlation in predicting pregnancy outcome. Although this study fails to provide a clear definition of the scope in predicting pregnancy abortion based on GSV:GV, it has provided a reasonable diagnostic basis for future research directions. The values of YS are important for deciding the pregnancy loss. A large number of case summaries can enable accurate prediction of pregnancy outcome as sample size impacts the prediction. In summary, the ratio of gestational sac volume to germ volume can predict spontaneous pregnancy abortion at the 6th week of gestation to a certain extent, providing a theoretical basis for clinical ultrasound pregnancy examination indicators. All the factors such as TVS images, GSV values, and GV and YS shape assist in identifying the pregnancy outcome: whether pregnancy is normal or abnormal and how it may contribute to pregnancy loss if it is abnormal.



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