Exposure to acute stress during early pregnancy could reduce a woman’s chances for delivering a baby boy and increase her risk for premature delivery.
Those are key findings from a study of how the 2005 Tarapaca earthquake in Chile– which was a magnitude 7.9 event – impacted pregnant women in the region. The findings, based on an analysis of birth certificates in Chile between 2004 and 2006, were reported online in the Dec. 7, 2011 issue of the journal Human Reproduction (Hum. Reprod. 2011 Dec. 7 [Epub doi: 10.1093/humrep/der390]).
“Generally, there are more male than female live births,” study coauthor Dr. Karine Kleinhaus, an assistant professor of psychiatry, obstetrics and gynecology, and environmental medicine at New York University, said in a statement. “The ratio of male to female births is approximately 51:49 — in other words, out of every 100 births, 51 will be boys. Our findings indicate a 5.8% decline in this proportion, which would translate into a ratio of 45 male births per 100 births, so that there are now more female than male births. This is a significant change for this type of measure.”
The finding supports previous research which found that male fetuses tend to grow larger than females and need more resources from the mother, and therefore are more likely to miscarry in times of stress. In addition, male fetuses may be less robust than females and may be less capable of adapting their development to a stressful environment in the womb.
”Our findings on a decreased sex ratio support this hypothesis and suggest that stress may affect the viability of male births,” said the study’s other coauthor, Florencia Torche, Ph.D, also of NYU. “In contrast, among female conceptions, stress exposure appears not to affect the viability of the conception but rather, the length of gestation.”
The study also revealed that women who experienced the earthquake during their second and third months of pregnancy had shorter pregnancies and were more likely to have premature babies.
— Doug Brunk
Image courtesy paparutzi’s photostream