Neonatal Mortality, the Male Disadvantage

Male infants have an excessive risk of neonatal death by comparison with females. It has never been clear whether this male disadvantage is due to specific disease processes or is a general biologic feature of being male. In an analysis of 2,735 consecutive newborn autopsies, the ratio of males to females was 1.28:, which differs significantly from the 1.05:1 ratio for all U.S. livebirths. There was a near equal male to female ratio for most disorders in stillborn infants while disorders arising after birth demonstrated a strong male disadvantage. The still-born ratios presumably reflect a predominant maternal influence while birth and removal from the maternal environment uncovers an inherent biologic disadvantage of being male, a disadvantage not selectively related to specific disease processes. This nonspecificity is confirmed by the finding of several disorders in which sex ratios for stillborns are quite different than the ratios recorded for liveborn infants. The sex ratio for liveborn Caucasians was significantly greater than for nonwhites, and the nonpoor had a significantly greater ratio than the poor. About half of these differences appear related to a greater incidence of prenatal bacterial infections in the poor and nonwhites.