According to the findings of a latest study, women who experienced higher levels of trauma gave birth to significantly smaller male babies.

In the first study of its kind, researchers from the Icahn School of Medicine at Mount Sinai have found significantly lower birth weights in male infants--an average decrease of 38 grams, or approximately 1.3 ounces--born to women who had been exposed to trauma at some point in their lives and who secreted higher levels of cortisol, a hormone related to stress, in late pregnancy.

Only women who had both a history of trauma and higher levels of cortisol secretion experienced lower birth weights; trauma alone was not sufficient. The association was also only seen among male babies. This is consistent with other data that shows that male fetuses are more susceptible to effects of maternal stress on intrauterine growth.

While the mechanisms remain unclear, trauma-related stress, even when occurring long before the woman becomes pregnant, can have lasting effects on regulatory systems involved in her day-to-day response to stress, including processes related to cortisol production.

Not everyone who experiences trauma develops disruption in their biological stress response systems but if they do, there can be health implications for both the woman and her child. Therefore, knowing about a pregnant woman's history of trauma together with stress hormone levels may identify at-risk pregnancies that may be complicated by low birth weight. "Our study highlights that experiences prior to pregnancy can shape the health of subsequent generations through altered fetal development and pregnancy outcomes," said the study's senior author, Rosalind Wright. 

"Given the disproportionate exposure to stressors among racial minorities and women of lower socioeconomic status, there are important implications for understanding intergenerational perpetuation of health disparities and for understanding how to intervene." Size at birth is a determinant of lifelong function, health, and disease. Minority women and those of disadvantaged socio-economic status are more likely to have low-birthweight infants. Chronic lifetime stress contributes to this risk. The study has been published in The Journal of Pediatrics.