Narrowing of sex differences in infant mortality in Massachusetts.

Objectives: To examine whether the improved survival of preterm infants has influenced the known male excess in infant mortality.

Study Design: We analyzed sex-specific infant mortality using linked birth and death certificates for all 619,811 live born infants in Massachusetts between 1989 and 1995.

Results: Between 1989 and 1995 the male excess in infant mortality decreased by 50%, from 1.6/1000 to 0.8/1000 live births (LB). This narrowing resulted primarily from a more rapid decline in neonatal mortality among male infants (1.5/1000 LB) than among female infants (0.9/1000 LB). The largest declines in the male excess in neonatal mortality occurred among very premature infants (GA < or = 30 weeks) and resulted primarily from a more rapid decrease in male deaths from respiratory distress syndrome.

Conclusions: The narrowing of the sex difference in mortality between 1989 and 1995 suggests that newer treatments like antenatal steroids, and surfactants may have differentially benefited male infants.