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A new study published in JAMA Network Open reveals that higher body mass index (BMI) in both men and women may be associated with reduced fertility and an increased risk of miscarriage. Conducted by researchers at Erasmus University Medical Centre in Rotterdam, the study highlights the importance of preconception health, particularly weight management, in improving pregnancy outcomes.
Study Overview
The population-based prospective cohort study, part of The Generation R Study Group, followed 3,604 women and their partners from August 2017 to July 2021. Participants were tracked from the preconception stage through pregnancy, with outcomes focusing on fecundability, subfertility, and miscarriage. Fecundability refers to the likelihood of conceiving within one month, while subfertility is defined as taking over 12 months to conceive or requiring assisted reproductive technology. Miscarriage was defined as the loss of pregnancy before 22 weeks of gestation.
Key Findings
The study found that higher preconception BMI in both men and women was linked to lower chances of conceiving and higher risks of subfertility:
- Fecundability: For each unit increase in BMI, fecundability decreased by 2% in women and 1% in men. Women with overweight or obesity had notably lower chances of conceiving within one month compared to those with normal weight.
- Women with overweight had a fecundability ratio of 0.88 (95% CI, 0.80-0.98), while women with obesity had a ratio of 0.72 (95% CI, 0.63-0.82).
- Subfertility: The odds of experiencing subfertility were significantly higher in women with overweight or obesity, as well as men with obesity. Women with overweight had a 35% higher risk of subfertility, while women with obesity had a 67% higher risk. For men, obesity increased subfertility odds by 69%.
- Miscarriage Risk: Women with higher BMIs were also more likely to experience miscarriages. The study reinforces the understanding that excess weight can pose challenges not only to conceiving but also to maintaining a healthy pregnancy.
Implications for Practice
The study authors, led by Dr. Aline J. Boxem and Dr. Vincent W. V. Jaddoe, emphasized the potential benefits of optimizing BMI for both partners before trying to conceive. “BMI outside of the normal category in women and men was associated with lower fecundability, subfertility, and increased odds of miscarriage. Optimizing BMI from the preconception period onward in women and men might be an important strategy to improve fertility and pregnancy outcomes,” the researchers noted.
Limitations and Considerations
While the study offers valuable insights, it also acknowledges certain limitations. The researchers noted that the generalizability of the results might be affected by the characteristics of the included participants, who tended to be younger and have lower BMIs compared to those excluded from the study. Additionally, some time-to-pregnancy data were collected retrospectively, which may have introduced inaccuracies. The observational nature of the study means that unmeasured confounding factors could also influence the findings.
Funding and Disclosures
The study was supported by grants from Erasmus University Medical Centre, Erasmus University Rotterdam, and the Netherlands Organisation for Health Research and Development. Drs. Boxem and Jaddoe disclosed receiving research funding from these organizations.
As rising rates of overweight and obesity continue to impact global health, this study underscores the importance of addressing weight-related fertility issues early, ideally before conception, to improve reproductive outcomes for both partners.
