Is body weight associated with a risk of ectopic pregnancy?

This study looked at how bodyweight affected ectopic pregnancy (EP) in women undergoing in vitro fertilization (IVF). It found that women with a low body weight have a higher rate of EP.

An ectopic pregnancy (EP) occurs when an embryo implants somewhere other than in the uterus. It occurs most often in the Fallopian tubes which lead from the ovaries to the uterus but can also occur within the abdomen. Embryonic tissue grows aggressively, which is dangerous when it occurs outside of the controlled environment of the uterus. An EP is treated with medication or surgery to terminate the pregnancy.

IVF embryo transfer leads to a higher rate of EP than natural conception. A transfer of multiple embryos can lead to both an EP and a normal pregnancy within the uterus. Bodyweight is related to pregnancy outcomes and may influence EP. It is not clear, however, whether bodyweight influences EP rates following IVF.

This study used records of 16,378 IVF pregnancies. Both fresh and frozen embryo transfers were used. The study did not include women with diabetes, thyroid disease, or unusually shaped uteruses. 2,155 cycles were from women with low body weight (body mass index; BMI under 18.5 kg/m²). 13,447 cycles were from women of normal weight (BMI between 18.5 and 24.9 kg/m²), and 776 cycles were of women who were overweight or obese (BMI over 25 kg/m²). 

A BMI between 22 and 24.5 kg/m² had the lowest rate of EP. Pregnancies of women of low weight had significantly more EPs than those of women of normal weight (2.92% vs. 2.02). This association remained significant after adjusting for factors including age, number of previous pregnancies, and IVF medications used. Low body weight was related to EP risk after both fresh and frozen embryo transfers.

The EP rate of women of high BMI was 2.84%. This was not considered statistically significant compared to women with normal BMI.

This study found that women who were underweight had a higher rate of ectopic pregnancies following embryo transfer.

There were few women with a high body weight in this study. Larger studies would be needed to tell if high body weight is also related to ectopic pregnancy risk.