Male infants are more likely to be born by spontaneous preterm birth than are female infants. Laboratory studies are also more likely to show evidence of placenta infection when infants are male, researchers report.

Lead investigator Dr. Robert L. Goldenberg told Reuters Health that the cause of most cases of preterm birth is unknown and the poorer pregnancy outcomes of male versus female infants is also unexplained.

Goldenberg, who is currently at Drexel University in Philadelphia, and colleagues determined if there was connection between placental tissue infection, inflammation and preterm birth.

The researchers studied the placentas and umbilical cords of 446 infants born between 23 to 32 weeks and found that male infants were significantly more likely to have placentas with positive cultures than were females, 63.4 percent versus 51.8 percent, respectively.

The males were more likely to have umbilical cord blood with evidence of bacterial infection with Mycoplasma hominis and Plasma urealyticum, at 27.6 percent versus 19.2 percent, respectively

The authors also found evidence to suggest that the mother’s immune response to fetal tissue may be more common in male fetuses, according to the report in the American Journal of Obstetrics and Gynecology.

Goldenberg added that “the greater risk of infection in preterm male versus female placentas, if substantiated, might provide some clues” to explain the increased preterm birth rate and the higher mortality in male fetuses and newborns.

SOIURCE: American Journal of Obstetrics, December 2006.