New US research has found that women who experience stress during their pregnancy are more likely to give birth to a girl than a boy and have a higher risk of birth complications.
Carried out by researchers at Columbia University Vagelos College of Physicians and Surgeons and New York-Presbyterian, the new study looked at 187 healthy pregnant women aged 18 to 45.
The team measured 27 indicators of psychosocial, physical, and lifestyle stress that might be affecting the women using questionnaires, diaries, and daily physical assessments and found that the majority of the women, nearly 67 percent, were healthy and unstressed.
However, around 17 percent of the women were psychologically stressed and experiencing high levels of depression, anxiety, and perceived stress, and 16 percent were physically stressed, with higher daily blood pressure and greater caloric intake compared with the healthy pregnant women.
In addition, the researchers also found that the pregnant women experiencing physical and psychological stress appeared to be less likely to give birth to a boy. Although, on average, around 105 males are born for every 100 female births, in this study the sex ratio among the physically and psychologically stressed groups was a male-to-female ratios of 4:9 and 2:3, respectively.
"Other researchers have seen this pattern after social upheavals, such as the 9/11 terrorist attacks in New York City, after which the relative number of male births decreased," says study leader Catherine Monk, Ph.D. "This stress in women is likely of long-standing nature; studies have shown that males are more vulnerable to adverse prenatal environments, suggesting that highly stressed women may be less likely to give birth to a male due to the loss of prior male pregnancies, often without even knowing they were pregnant."
The findings, published online in the journal PNAS (the Proceedings of the National Academy of Sciences), also showed that mothers who were psychologically stressed had more birth complications than those who were physically stressed, and physically stressed mothers were more likely to give birth prematurely than the unstressed mothers.
The fetuses of of physically stressed mothers also had reduced heart rate-movement coupling -- which indicates a slower development of the central nervous system development -- compared with unstressed mothers.
However, the negative effect of stress appeared to be offset by social support from friends and family. For example, the more social support a mother received, the more she was likely to give birth to a boy.
"Screening for depression and anxiety are gradually becoming a routine part of prenatal practice," says Monk. "But while our study was small, the results suggest enhancing social support is potentially an effective target for clinical intervention."