P-469 Body mass index impacts ectopic pregnancy during in vitro fertilization: are we jumping the gun? An analysis of 42,362 clinical pregnancy cycles
Authors: Bu Z , Ge X , Sun Y 
Published: June 2023

Study question

Does female body mass index (BMI) have impact on ectopic pregnancy (EP) in women undergoing in vitro fertilization (IVF) and embryo transfer (ET) treatment?

Summary answer

EP rate is higher in underweight patients in fresh cycles. However, BMI is not a risk factor for EP after controlling confounders.

What is known already

It has been shown that tubal factor infertility, stage of embryos transferred (cleavage stage or blastocyst stage), high estrogen levels during ovarian stimulation, and endometrial thickness, have impact on EP rate in IVF cycles. In addition, other potential factors including ovarian stimulation protocols, number of embryos transferred, and type of embryos (fresh or frozen thawed) are also seemed to be associated with EP rate. However, BMI has interactions with these confounding factors mentioned above.

Study design, size, duration

This was a retrospective cohort study. From January 2010 to June 2022, patients between the ages of 20 and 45 years who had their first fresh/frozen thawed ET cycles, and reported as clinical pregnant were included. BMI was categorized into three groups: underweight (&lt; 18.5 Kg/m2), normal weight (18.5–23.9 Kg/m2), overweight and obesity (≥ 24 Kg/m2).

Participants/materials, setting, methods

A total of 42,362 cycles were included in the final analysis. The overall ectopic pregnancy rate was 2.57% (1,089/42,362). Firstly, possible factors affecting ectopic pregnancy were screened in both fresh and frozen thawed ET cycles. Then, multivariate logistic regression analysis was used to adjust confounding risk factors.

Main results and the role of chance

EP rates in fresh, and frozen thawed transfer cycles were 2.43% (672/27,600) and 2.82% (417/14,762), respectively. In fresh ET cycles, the ectopic pregnancy rate was significantly higher in underweight patients when compared with that in normal and overweight/obesity patients (3.29% vs. 2.29% vs. 2.54%; P = 0.029). However, the ectopic pregnancy rate was not differ among patients with different BMI (2.72% vs 2.76% vs 2.96%; P = 0.782) in frozen thawed cycles. In fresh ET cycles, secondary infertility, tubal infertility, elevated estrogen level, thin endometrial thickness, and cleavage stage embryo transfer were risk factors with ectopic pregnancy. However, female BMI was not associated with ectopic pregnancy (adjusted OR: 0.98, P = 0.894, for BMI 18.5-23.9 Kg/m2; adjusted OR: 0.89, P = 0.205, for BMI ≥ 24 Kg/m2. Reference = BMI &lt; 18.5 Kg/m2). In frozen thawed embryo transfer cycles, only thin endometrial thickness, and cleavage stage embryo transfer were risk factors with ectopic pregnancy. Female BMI was not predictable for ectopic pregnancy, either (adjusted OR: 1.15, P = 0.513, for BMI 18.5-23.9 Kg/m2; adjusted OR: 1.24, P = 0.367, for BMI ≥ 24 Kg/m2. Reference = BMI &lt; 18.5 Kg/m2).

Limitations, reasons for caution

This is a retrospective study with 12 years period. New embryo culture methods and embryo transfer strategy emerged. It is possible that not all confounders have been controlled. Meanwhile, the definition of tubal infertility and pelvic disease need more caution as the lack of laparoscopic examination in some cases.

Wider implications of the findings

Understanding the impact of BMI on EP during IVF treatment may be useful for predicting results. At the first glance, underweight patients are more likely to encounter with EP during fresh ET. However, it is the high estrogen level, but not low BMI, that contributes to this phenomenon.

Trial registration number

N/A