Abnormal BMI Linked to Lower Fertility and Higher Miscarriage Rates: Study Reveals

"Improving BMI in both women and men from the preconception period onward could be a key strategy for enhancing fertility outcomes," the researchers wrote.

Obesity in women is linked to decreased fertility and a higher risk of miscarriage. These associations may also extend across all BMI categories and also affect men. Considering this, Aline J. Boxem, The Generation R Study Group, Erasmus University Medical Centre, Rotterdam, the Netherlands, and colleagues examined the relationships between preconception BMI in both partners and time to pregnancy and miscarriage.

For this purpose, the researchers conducted a population-based prospective cohort study in Rotterdam, the Netherlands, from August 9, 2017, to July 1, 2021, involving 3,604 women and their partners. They were followed from the preconception period until birth. BMI was measured during preconception or early pregnancy.

The main outcomes included fecundability, defined as the probability of conceiving within one month; subfertility, defined as taking more than 12 months to conceive or using assisted reproductive technology; and miscarriage, defined as pregnancy loss before 22 weeks of gestation. These outcomes were evaluated through questionnaires and obstetric caregiver records, with the analysis conducted on July 12, 2024.

The study led to the following findings:

• Time-to-pregnancy analysis included 3,033 episodes among women (median age 31.6 years, median BMI 23.5) and 2,288 episodes among men (median age 33.4 years, median BMI 24.9).
• For miscarriage analysis, there were 2,770 pregnancy episodes among women (median age 31.5 years, median BMI 23.5) and 2,189 among men (median age 33.5 years, median BMI 25.0).
• Higher BMI in both women and men was linked to lower fecundability; specifically, for each unit increase in BMI, fecundability decreased (fecundability ratio [FR]: women, 0.98; men, 0.99).
• Women with overweight (FR, 0.88) and obesity (FR, 0.72) had significantly lower fecundability compared to those with normal weight.
• When compared to women with normal weight, those who were underweight (odds ratio [OR], 1.88), overweight (OR, 1.35), or obese (OR, 1.67) had increased odds of subfertility.
• In men, obesity was also associated with greater odds of subfertility (OR, 1.69).
• Regarding miscarriage, women with overweight (OR, 1.49) and obese (OR, 1.44) faced increased odds compared to those of normal weight.

"In the cohort study, we found that BMI outside the normal range in both women and men was linked to lower fecundability, higher rates of subfertility, and increased odds of miscarriage. Optimizing BMI from the preconception period onward may be a key strategy for improving fertility and pregnancy outcomes in both genders," the researchers concluded.

Reference:

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