Sex ratio is remarkably constant.

To study whether the sex of the offspring is related to increasing parental age, gravidity, and parity, hypothesizing an altered male-to-female sex ratio with the advancing parental age.A large retrospective cohort study.The study analyzed birth records of Hadassah Hebrew University Medical Center in Jerusalem from June 2003 to December 2006.35,837 birth records were analyzed including 941 multifetal deliveries, excluding foreign inhabitants (n = 744), missing data for the main study outcome (n = 2) and parturients over 50 years to control for egg donation (n = 26).None.Male-to-female sex ratio.The male-to-female sex ratio of all the newborns was 1.05. This ratio did not change significantly with either maternal or paternal age. Neither gravidity nor parity affected the male-to-female ratio. The only factor that affected the regression of sex ratio was the length of gestation.Sex ratio at birth is remarkably constant. No association was found between parental age or birth order and neonatal sex ratio.