Prospective Randomized Control Study of Two Different Types of Luteal Phase Support in Natural Cycle Frozen Embryo Transfer and Its Effect on Pregnancy Rates
Phase: NA
Conditions: Luteal Phase Support
Sponsor: Shaare Zedek Medical Center

Prospective randomized control study of two different types 
of luteal phase support in natural cycle frozen embryo 
transfer (FET) and its effect on pregnancy rates 
 
The ability to transfer frozen embryos makes it possible to keep frozen the amount of 
embryos created in in-vitro-fertilization (IVF) treatments for later use. Advantages of 
frozen embryos transfer (FET) include reduced embryo loss after IVF and a higher 
pregnancy rate. The rate of frozen embryos transfer has increased in recent years 
due to a higher tendency of single embryo transfer (SET), use of preimplantation 
genetic testing, and prevention of ovarian hyperstimulation (1,2). Due to 
developments of freezing technology and techniques in recent years, embryo 
freezing enables the advantages mentioned above without compromising the 
pregnancy rate (3). 
There are different methods to prepare the endometrium for FET: 
1. Natural cycle (NC) - Timing of ovulation by diagnosing the luteinizing hormone 
(LH) Surge. The advantage of a NC is the natural preparation of the body for 
implantation without the need for medicinal intervention. The disadvantage is need of 
intense monitoring to detect ovulation and inflexibility of day of embryo transfer. As a 
result, NC results in higher percentages of cycle cancellation. 
2. Modified natural cycle (mNC) - Inducing ovulation by administration of Human 
Chorionic Gonadotropin (HCG) trigger. The advantage of ovulation induction with 
HCG is greater flexibility and ability to plan transfer day according to the availability of 
the system, with fewer visits by the patient. 
3. Medical - preparation of endometrium with estrogen and progesterone. This 
method is suitable for women who do not ovulate regularly. This allows flexibility of 
the treatment with fewer cycle cancellations. 
Studies that compared pregnancy outcomes of natural versus adapted NC are 
inconclusive (4-8). In recent years, several studies showed higher clinical pregnancy 
and ongoing pregnancy rates in NC group compared to group treated with HCG for 
ovulation induction (7-8). 
Recently, several studies showed advantages of FET in NCs. A study published in 
April 2020 by XITONG LIU in Fertility and Sterility showed a higher rate of live births 

and a reduced rate of miscarriages in NC FET group compared to the drug-treated 
group (9). Additional studies showed higher rates of gestational hypertension (10 -
11), macrosomia and post-term pregnancies in the medicated FET groups (10). 
Endogenous progesterone secreted by the corpus luteum after natural ovulation is 
expected to provide an adequate luteal support as in spontaneous pregnancies. 
Therefore, it is assumed that there is no need for luteal support when embryos are 
transferred in NCs, and the benefit of medical luteal support is not conclusive (12-
15). Nevertheless, a meta-analysis published in Human Reproduction in 1202, 
examined the effect of luteal support with progesterone and showed higher 
pregnancy rates in the group that received luteal support compared to those who did 
not receive it (16). It should be noted that most of the studies were performed with 
induction of ovulation by HCG. 
Administration of HCG for luteal support is used both in fresh and frozen cycles. A 
previous study showed higher ongoing pregnancy rates in a group that received HCG 
within the day of natural LH surge together with vaginal progesterone from the day of 
embryo transfer compared to luteal support with progesterone alone. The use of 
1500 units of HCG on cycle day 18 and 21 resulted with a significant increase in 
serum progesterone levels (17). 
Administration of Gonadotropin Releasing Hormone (GnRH) analog as a treatment 
for luteal support in fresh IVF cycles has shown higher clinical pregnancy, multiple 
pregnancies, and live birth rates (18). When GnRH agonist is used (as single or 
repeated doses) it may cause an increase in LH secretion by the pituitary gland 
which augments the function of the corpus luteum and may lead to direct local 
stimulation of the endometrium [19]. 
In 2015, a retrospective cohort study from Israel compared the use of progesterone 
versus administration of HCG and GnRH agonist in NC FET. They showed a higher 
clinical pregnancy rate in the group treated with GnRH agonist and HCG (20). 
Another randomized prospective controlled showed that the addition of a GnRH 
agonist to luteal support with HCG compared with HCG alone in NC FET increased 
clinical pregnancy and implantation rates when frozen cleavage stage embryos were 
transferred (21). In 2016, a randomized prospective study from Finland examined the 
use of GnRH agonists in addition to standard vaginal progesterone support 
compared to a group treated with progesterone alone in 98 women undergoing NC 
FET (22). Both clinical and ongoing pregnancy rates were higher in the group treated 

with GnRH agonists, but due to small sample size, the difference was not statistically 
significant.  
It is important to note that GnRH agonists are not considered teratogenic (23). In 
over 340 women exposed to GnRH agonists in the mid-luteal phase, the rate of birth 
defects and miscarriages (2.5% and 15%, respectively) was similar to the general 
IVF population (24-26). 
There is a need for further research to examine the effectiveness of GnRH agonist 
treatment as luteal support in in NCs FET. Conducting a prospective randomized 
controlled study will allow to determine the treatment efficacy of GnRH agonist and 
HCG in relation to the standard luteal support with progesterone. 
The aim of the study is to compare the pregnancy rate between women treated with 
GnRH agonist together with HCG and standard luteal support with progesterone in 
the return of frozen embryos in natural cycles and in vitro fertilization treatments. 
 
Primary outcome 
- 
Clinical pregnancy rate – visualization of intrauterine gestational sac on 
ultrasound divided by number of transfers 
Secondary outcomes 
- 
Overall pregnancy rate - number positive bHCG divided by total number of 
transfers 
- 
Ongoing pregnancy rate – visualization of fetal cardiac activity divided by total 
number of transfers  
- 
Implantation rate – number of gestational sacs divided by number of embryos 
transferred 
- 
Ectopic pregnancy rate – number of ectopic pregnancy divided by number of 
positive bhCG  
- 
Miscarriage rate – number of non-viable before 24 weeks divided by total 
number of positive bhCG 
- 
Live birth rate – number of live births after 24 weeks divided by number of 
transfers. 

Study methods 
Women who undergo natural cycle FET at the IVF center in Shaare Zedek Medical 
Center will be recruited.  
During the visit to the clinic, the women's demographic and clinical data will be 
collected. The women who are found to be suitable according to the research criteria 
will receive an explanation of the nature of the study and will sign a consent form for 
participation in the study in accordance with the procedures of the Institutional 
Helsinki Committee.  
The women can give an agreement until the ET day.  
The number of embryos that will be returned will be determined according to the age 
of the woman, the number of treatment cycles and the quality of the embryos in 
accordance with the accepted policy in the unit.  
The distribution of the patients to the two study groups will be done randomly by 
computer in a ratio of 1:1. Sealed envelopes containing information regarding the 
type of treatment for luteal support will be attached to the consent forms. 
144 women will be divided into two groups, and each group will receive a different 
luteal treatment: 
Study group – patients will receive luteal support of GNRH agonist andHCG 
according to departmental protocol: 
Cleavage stage embryo:  
- 
ET day (embryo day 2-3) - Ovitrelle 125mcg 
- 
Day 3 after ET - Ovitrelle 125mcg + Decapeptyl 0.1mg 
- 
Day 6 after ET- Ovitrelle 125mcg  
- 
Day 9 after ET - Ovitrelle 125mcg 
Embryo blastocyst stage:  
- 
ET day (embryo day 5-6) - Ovitrelle 125mcg + Decapeptyl 0.1mg  
- 
Day 3 after ET - Ovitrelle 125mcg  
- 
Day 6 after ET - Ovitrelle 125mcg 
Control group - patients will receive luteal support of vaginal progesterone – 100 mg 
Endometrin twice daily until week 8 of pregnancy. 

Clinical pregnancy will be defined as the demonstration of an intrauterine gestational 
sac. Other pregnancy outcomes will be received in a telephone conversation with the 
patients and computer database nine months after the treatment. 
  
Statistical calculations 
Based on the clinical pregnancy rate in the prospective study by Bjuresten, et al [13], 
where a clinical pregnancy rate of 32% was found among women treated with  
progesterone for luteal support, and given an alpha of 5% and a power of 80%, 144 
women (72 women in each group) are required in order to demonstrate a clinical 
pregnancy rate of 55% in the study group. 
Comparison of categorical variables will be carried out using the CHI-SQUARE 
TEST. Comparison of continuous variables will be performed using the Students t-
Test or Mann–Whitney U method depending on the variable distribution (normal vs. 
non-normal distribution, respectively). A multivariate regression will also be 
conducted in order to determine which variables are significantly and independently 
related. Statistical significance will be defined when P values are less than 0.05 
 
Inclusion Criteria 
- Normo-ovulatory women 
- Women undergoing frozen embryos transfer in a natural cycle 
- Age 18-45 
- BMI 18-35 
 
Exclusion Criteria 
- Women undergoing medicated frozen embryos transfer 
- Women with a BMI over 35 or under 18. 
- Women with hydrosalpings 

- Women with defects or uterine malformations (congenital) or acquired such as 
myomas 
- Egg donation and surrogacy 
- Use of preimplantation genetic testing  
Pregnant women, children and those lacking judgment will not participate in the 
experiment. 
 
 
 
 

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