Secondary sex ratio is not related to fertility in Italian women

Objective: To test whether the secondary sex ratio (proportion of male births) is associated with time to pregnancy, a marker of fertility. Design: Analysis of four large population surveys. Setting: Denmark and the United Kingdom. Participants: 49 506 pregnancies. Main outcome measure: Secondary sex ratio. Results: No association was found between the sex ratio and time to pregnancy and no discernible trend was found for sex ratio with time to pregnancy, either within individual datasets or in the pooled analysis. The odds ratios were 0.97 (95% confidence interval 0.90 to 1.04) for contraceptive failures, 1.01 (0.96 to 1.05) for time to pregnancy of 2-4 months, 1.02 (0.97 to 1.08) for 5-10 months, 0.98 (0.93 to 1.03) for 11 months or more, and 0.88 (0.74 to 1.06) for fertility treatment, with 0-1 months as the reference category. Conclusion: No association was found between the secondary sex ratio and time to pregnancy.