Higher BMI in women, men tied to longer time to pregnancy, increased miscarriage odds
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Key takeaways:
- Women with overweight or obesity had a lower probability of pregnancy within 1 month and increased odds of subfertility.
- Higher BMI was also associated with increased odds of miscarriage.
BMI in the overweight or obese range for both women and men during preconception or early pregnancy was linked to time to pregnancy success and miscarriage risk, according to study results published in JAMA Network Open.
“In previous research, the association of BMI outside of the normal range with fertility outcomes in the general population was not yet fully established, and the association of male BMI independent of female BMI on fertility outcomes was not clear,” Aline J. Boxem, MD, and Vincent W. V. Jaddoe, MD, PhD, of the department of pediatrics and the Generation R Study Group at Erasmus University Medical Centre, the Netherlands, told Healio. “In this study, we observed that separate and combined female and male BMI outside the normal range was associated with fertility outcomes. This means that when providing preconception counselling, we should not only focus on obesity in women, but BMI across the full range, and the independent effect of male BMI on fertility outcomes. When female and/or male BMI is outside of the normal range, one could consider focusing on weight loss or gain before actively trying to conceive in order to improve fertility outcomes.”
Boxem and colleagues conducted a population-based prospective cohort study with 3,604 women and their partners who were pregnant (52.8% in the first trimester) or actively trying to conceive (33.2%) from August 2017 to July 2021 in Rotterdam, the Netherlands. Researchers followed women and partners from the preconception period until childbirth. Couples could participate more than once for different preconception or pregnancy episodes. The time-to-pregnancy analysis included 3,033 episodes among women and 2,288 episodes among male partners. The study population for miscarriage analysis included 2,770 pregnancy episodes among women and 2,189 pregnancy episodes among male partners.
Participants completed questionnaires on time to pregnancy and mode of conception. Fecundability was defined as the probability of conception within 1 month; subfertility as more than 12 months of time to pregnancy or duration of actively pursuing pregnancy or assisted reproductive technology use and miscarriage as pregnancy loss at less than 22 weeks’ gestation.
Primary outcome was fecundability, subfertility and miscarriage rates.
For every BMI unit increase, fecundability decreased for both women and men, with fecundability ratios of 0.98 and 0.99, respectively. Compared with women with normal weight, women with overweight and obesity had lower fecundability ratios of 0.88 and 0.72, respectively. In analyses that combined BMI categories for both partners, overweight and obesity decreased fecundability in men only, with a fecundability ratio of 0.89 vs. normal weight in both partners.
Higher BMI was associated with subfertility for both women (OR = 1.04; 95% CI, 1.02-1.05) and men (OR = 1.03; 95% CI, 1-1.06). Women with underweight (OR = 1.88; 95% CI, 1.22-2.88), overweight (OR = 1.35; 95% CI, 1.11-1.63) and obesity (OR = 1.67; 95% CI, 1.3-2.13) had increased odds of subfertility compared with women with normal weight. Men with obesity had increased odds of subfertility compared with men with normal weight (OR = 1.69; 95% CI, 1.24-2.31).
In analyses that combined BMI categories of both partners, overweight and obesity in both partners was associated with subfertility compared with normal weight in both partners (OR = 1.41; 95% CI, 1.06-1.87).
“We observed the strongest associations with subfertility when overweight and obesity was present in both partners,” the researchers wrote. “This finding emphasizes the potential independent negative association of male BMI with fertility, possibly owing to lower sperm quality.”
Women with overweight vs. normal weight had increased miscarriage probability per week (HR = 1.43; 95% CI, 1.1-1.86). Women with overweight (OR = 1.49; 95% CI, 1.12-1.98) and obesity (OR = 1.44; 95% CI, 1-2.08) had increased odds of miscarriage compared with women with normal weight.
“To move forward in this research and to strengthen these results, a larger sample size is needed. Furthermore, we propose to examine the associations between biomarkers associated with metabolic syndrome and miscarriage risk, independent of BMI,” Boxem and Jaddoe told Healio. “Randomized controlled trials are needed to assess the effects of preconception lifestyle interventions provided to both women and men, focused on lifestyle factors such as achieving BMI within a normal range.”