New research supports the notion that extreme stress early in pregnancy may be linked to increased risk of preterm delivery. And, population wide, acute exposure to such stress could lead to the birth of fewer male babies than females.

While each of these phenomena had been investigated in earlier studies, the two had not been examined together in a single study. Researchers at New York University analyzed data for three sets of women: 6,874 who were pregnant when a major earthquake occurred in Chile in 2005 and who lived near enough to be affected by that event; 7,115 women whose pregnancies coincided with those of the first group but who were not affected by the quake; and a control group of 3,649 women whose pregnancies occurred during the same nine months as those of the first group but a full calendar year earlier.

Earthquakes, the paper notes, are regarded as extremely stressful events for humans.

The data revealed a substantial decrease in gestational age (the number of weeks from the mother’s last menstrual period, in this case measuring how many weeks “old” the baby is at birth) and an increase in preterm deliveries among women who were pregnant with female babies and who experienced the earthquake during the second or third month of their pregnancy. No such association was found for those pregnant with male babies. That result was striking, the authors note, because among the general population, male babies are more likely to be delivered preterm than females.

And, as suspected, the ratio of male to female babies born to the group exposed to the earthquake during the third month of pregnancy was smaller than that for the other groups.

The authors note that their work could aid in the development of interventions to prevent preterm births, which can have lasting and serious health consequences for babies.

The study was published Thursday in the journal Human Reproduction.