For women and men, body mass index (BMI) outside of the normal range is associated with increased time to pregnancy and odds of miscarriage, according to a study published online Sept. 19 in JAMA Network Open.

Aline J. Boxem, M.D., from the Erasmus University Medical Center in Rotterdam, Netherlands, and colleagues conducted a population-based prospective cohort study to examine the associations of preconception BMI in both partners with time to pregnancy and odds of miscarriage. Data were included for 3,604 women and their partners who were followed from the preconception period until birth.

The time-to-pregnancy analyses included 3,033 episodes among women and 2,288 episodes among men, and the miscarriage analyses included 2,770 pregnancy episodes among women and 2,189 among men. The researchers observed an association for higher BMI in women and men with lower fecundability (fecundability ratio [FR], 0.98 and 0.99 in women and men, respectively, per unit increase in BMI).

Lower fecundability was seen for women with overweight and obesity versus those with normal weight (FR, 0.88 and 0.72, respectively). Increased odds of subfertility were seen in association with underweight, overweight, and obesity compared with normal weight in women (odds ratios, 1.88, 1.35, and 1.67, respectively).

Obesity was associated with increased odds of subfertility in men (odds ratio, 1.69). Overweight and obesity were associated with increased odds of miscarriage compared with normal weight in women (odds ratios, 1.49 and 1.44, respectively).

“Optimizing BMI from the preconception period onward in women and men might be an important strategy to improve fertility and pregnancy outcomes,” the authors write.

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