Low body mass index is associated with ectopic pregnancy following assisted reproductive techniques: a retrospective study.

OBJECTIVE

To investigate the association between body mass index (BMI) and ectopic pregnancy (EP) following embryo transfer (ET).

DESIGN

Retrospective cohort study.

SETTING

University-affiliated hospital.

POPULATION: A total of 16 378 pregnancies derived from either fresh ET or frozen-thawed ET between January 2008 and December 2017.

METHODS

We used the generalised estimating equation (GEE) to analyse the association between BMI categories and EP, as one woman may contribute to more than one pregnancy. Generalised additive models were also used to demonstrate the non-linear association. Models were adjusted for age, parity, gravidity, previous history of ectopic pregnancy, duration of infertility, polycystic ovary syndrome, endometriosis, diagnosis of tubal problems, ovarian reserve markers, ovarian stimulation parameters, insemination protocol, endometrial thickness and embryo transfer policies.

MAIN OUTCOME MEASURES: Ectopic pregnancy.

RESULTS

According to the WHO criteria, the number of cycles with low (<18.5 kg/m2 ), normal (18.5-24.9 kg/m2 ) and high (≥25 kg/m2 ) BMI were 2155, 13 447 and 776, respectively. In comparison with the normal BMI group, the rate of EP was significantly increased in the low BMI group (2.92% versus 2.02%, relative risk 1.45, 95% CI 1.11-1.90), but not in the high BMI group (2.84%, relative risk 1.41, 95% CI 0.92-2.20). Adjusted for confounding factors, the odds ratio for EP comparing low BMI versus normal BMI was 1.61 (95% CI 1.19-2.16) and that comparing high BMI versus normal BMI was 1.12 (95% CI 0.72-1.76).

CONCLUSIONS

Low BMI is associated with an increased risk of EP.

TWEETABLE ABSTRACT: The ectopic pregnancy rate after embryo transfer for lean women is higher than that for women of normal weight.