Background: Obesity is increasing rapidly among women all over the world. Obesity is a known risk factor for subfertility due to anovulation, but it is unknown whether obesity also affects spontaneous pregnancy chances in subfertile, ovulatory women.
Methods: We evaluated whether obesity affected the chance of a spontaneous pregnancy in a prospectively assembled cohort of 3029 consecutive subfertile couples. Women had to be ovulatory and had to have at least one patent tube, whereas men had to have a normal semen analysis. Time to spontaneous ongoing pregnancy within 12 months was the primary endpoint.
Results: The probability of a spontaneous pregnancy declined linearly with a body mass index (BMI) over 29 kg/m(2). Corrected for possible related factors, women with a high BMI had a 4% lower pregnancy rate per kg/m(2) increase [hazard ratio: 0.96 (95% CI 0.91-0.99)].
Conclusions: These results indicate that obesity is associated with lower pregnancy rates in subfertile ovulatory women.