Female babies with congenital diaphragmatic hernia (CDH) are slightly more likely to die within 30 to 60 days of birth than male babies with the same condition, according to a recent Johns Hopkins Children’s Center study, which used medical records from an international registry.

In examining the role biological sex plays in outcomes for infants with CDH, investigators found that females have about a 32% higher risk of dying than males. The researchers say it’s a small but significant difference, and that the origins are unclear but may be linked in part to overall lower birth weights for female newborns.

CDH, which Johns Hopkins experts say affects an estimated 1 in 4,000 live births annually in the United States, has a historically high mortality rate of 30% or more. Thought to be rooted in genetic alterations that affect organ development during pregnancy, the condition is marked by defects in formation of the diaphragm — a large muscle that separates the chest from the abdomen and that is vital to breathing. The developmental damage leaves a hole in the muscle — a rupture that allows the intestines, stomach, liver and other abdominal organs to protrude into the chest. Most significantly, it impairs an infant’s normal lung development.

While some previous studies showed that male babies are more likely than female babies to have CDH, the impact of sex on a patient’s survival has been unclear from other studies.

“Although racial and ethnic outcome disparities have been documented in CDH, disparities between males and females are not well known. It is really important to understand if those disparities exist, because it may change how we can better manage these patients,” says Shaun Kunisaki, a senior author of the study, which appeared in The Journal of Pediatrics.

One possible intervention is to raise awareness among physicians who care for people who are pregnant and newborns, says Kunisaki, director of the congenital diaphragmatic hernia program at Johns Hopkins Children’s Center.

“It may be that we need to be more aggressive in treating female CDH patients than we currently are,” he says. “That may mean using medications to optimize lung function, and developing different clinical criteria for placing female patients with CDH on ECMO [a heart-lung machine] to protect their lungs.”