We appreciate the interest of Drs MI and Das in our recently published study, entitled “Impact of fetal gender on the labor curve” in the American Journal of Obstetrics and Gynecology, as well as the opportunity to respond to their comments.

It is true that we found that male fetuses, on average, weighed 89 g more than females. We also examined the differences between the groups in rates of comorbidities that you mentioned, but in fact found no differences in rates of gestational diabetes or hypertensive diseases of pregnancy. However, because observational data create the potential for inequality between comparison groups as you have highlighted, it is important to interpret the adjusted analyses. In this case, the best estimate of the relationship between first stage labor curve and fetal gender is that which accounts for potentially confounding factors such as group differences and many of the factors which you have raised concern for. The small, but statistically different medians in first stage labor progress between women carrying males compared with females were found while adjusting for parity, regional anesthesia, prostaglandin use, birthweight, and race. Labor type (induction vs augmentation vs spontaneous) was not a significant factor and did not remain in the final model. Although we were able to adjust for need for cervical ripening, we were not able to adjust for “unnatural contractions,” as this is not an entity recognized at our institution.

Finally, we apologize for any confusion, but this was a cohort study of consecutive term deliveries from the second stage, thus there were no patients with active phase arrest.