Sex differences in short term outcomes of very low birthweight infants: the newborn male disadvantage (2000; 83: F182-5)
Newborn boys, particularly those born very prematurely, seem to be more susceptible to death and illness than girls, finds new research. The study, published in the Fetal and Neonatal Edition of the Archives of Disease in Childhood, shows that this is in spite of improvements in technology and drug treatments.
The records of over 6,500 babies up to two weeks old, admitted to 12 different centres in the USA over a period of two years, were analysed. The babies had all been born prematurely and weighed well below the normal average (3 kilos) They were monitored until four months of age.
The boys' mothers were less likely to have taken steroids just before labour to help mature the babies' lungs, but otherwise there were few antenatal differences between the two sexes. Death rates were higher among the boys, with around one in four of them dying compared with one in seven of the girls. This difference was obvious as early as three days of age.
Boys were also at greater risk of complications. They had poorer lung function and needed more help with breathing. And they were more likely to have been resuscitated than girls. They also had more urinary tract infections and bleeding into the brain.
Whether Nature is weeding out the less fit males, so ensuring the survival advantage of the next generation, is unclear, say the authors. "The biological mechanisms contributing to the male disadvantage or female advantage have not been elucidated. Until science can rationalise the male and female circumstances, nature's intent will remain obscure," they conclude.