Early-pregnancy BMI linked to miscarriage and time to pregnancy

Early-pregnancy BMI linked to miscarriage and time to pregnancy | Image Credit: © rocketclips - © rocketclips - stock.adobe.com.

There is a link between time to pregnancy and miscarriage with body mass index (BMI) outside of the normal category in women and men during the preconception or early-pregnancy periods, according to a recent study published in JAMA Network Open.1

Obesity remains a significant public health concern among reproductive-aged women, with gestational hypertensive disorder, adverse birth outcome, and cardiovascular disorder risks increased from obesity during pregnancy. Additionally, growing data has indicated BMI in both men and women may be associated with early-pregnancy outcomes.²

Currently, understanding of the separate and combined associations of BMI in women and men with pregnancy outcomes remains lacking.¹ Therefore, investigators conducted a study to evaluate these associations.

Data was obtained from the Generation R Next Study, a population-based prospective cohort study aiming to identify preconception and early-pregnancy determinants of certain pregnancy outcomes. Participants included women and their partners aged at least 18 years residing in Rotterdam and trying to conceive or currently pregnant.

Of participants, 33.2% were in preconception and 52.8% were in the first trimester. Exclusion criteria included lacking BMI data, lacking time to pregnancy data, and not having a pregnancy at the end of the study phase.

BMI was determined through height and weight measurements without shoes and heavy clothing. For women, measurements occurred at enrollment and subsequent preconception or early-pregnancy visits. For men, measurements occurred during the first trimester visit.

Categories of BMI included underweight for less than 18.5, normal weight for 18.5 to 24.9, overweight for 25 to 29.9, and obesity for 30 or higher. Questionnaires in the preconception and early-pregnancy periods were used to determine time to pregnancy and mode of conception.

The start date of actively pursuing pregnancy and the first day of the last menstrual period were used to calculate the time to pregnancy. A time to pregnancy of 12 months or less was considered fertile, while not conceiving during this period or using assisted reproductive technology was considered subfertile.

Investigators defined miscarriage as, “pregnancy loss before 22 weeks of gestation,” with obstetrical caregivers consulted to obtain miscarriage data. Covariates included age, ethnicity, and highest level of education.

There were 3033 episodes among women included in the analyses for time-to-pregnancy. Women were aged a median 36.1 years and had a median BMI of 23.5. In comparison, 2288 episodes among men aged a median 33.4 years and with a median BMI of 24.9 were included.

For miscarriage analyses, there were 2770 pregnancy episodes among women aged a median 31.5 years and with a median BMI of 23.5. There were also 2189 episodes among men aged a median 33.5 years and with a median BMI of 25.

A median time to pregnancy of 3.7 months was reported, with 17.8% of episodes among women being subfertile and 11.3% leading to a miscarriage. The fecundability ratio (FR) among women was 0.98 vs 0.99 among men.

When determining the FR based on weight, fecundability was reduced among women with overweight and obesity vs normal weight. The odds of subfertility were also increased among patients with a higher BMI, with an odds ratio (OR) of 1.04 for women and 1.03 for men.

The ORs for subfertility among women with underweight, overweight, and obesity vs normal weight were 1.88, 1.35, and 1.67, respectively. Additionally, being overweight was linked to increased miscarriage odds, with a hazard ratio of 1.43. The small number of women with underweight or obesity in the study population may explain this data.

These results indicated reduced fecundability, subfertility, and increased miscarriage risk from BMI outside the normal category in women and men. Investigators concluded optimizing BMI from preconception onward may be key to improving pregnancy outcomes.

References

1. Boxem AJ, Blaauwendraad SM, Mulders AGMGJ, et al. Preconception and early-pregnancy body mass index in women and men, time to pregnancy, and risk of miscarriage. JAMA Netw Open. 2024;7(9):e2436157. doi:10.1001/jamanetworkopen.2024.36157
2. WiseLA, RothmanKJ, MikkelsenEM, SørensenHT, RiisA, HatchEE.An internet-based prospective study of body size and time-to-pregnancy.Hum Reprod. 2010;25(1):253-264. doi:10.1093/humrep/dep360