Researchers assessed 187 healthy pregnant women between 18 and 45 years of age. About 17% were mentally stressed, with high levels of depression, anxiety and perceived stress. Sixteen percent were physically stressed, with higher daily blood pressure and calorie intake than other women in the study. Women with either physical or psychological stress were more likely to have a girl, the study found. Typically, about 105 males are born for every 100 females. But the male-to-female ratios in this study were 4:9 among women with physical stress and 2:3 among those with mental stress during pregnancy.
“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,” said study leader Catherine Monk, director of Women’s Mental Health at New York-Presbyterian/Columbia University Irving Medical Center.
“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 Monk. “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.”
Other Impacts of Stress
- Physically stressed mothers, with higher blood pressure and caloric intake, were more likely to give birth prematurely than unstressed mothers.
- Among physically stressed mothers, fetuses had reduced heart rate-movement coupling — an indicator of slower central nervous system development — compared with unstressed mothers.
- Psychologically stressed mothers had more birth complications than physically stressed mothers.
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An estimated 30% of pregnant women report psychosocial stress from job strain or related to depression and anxiety, according to the researchers. Such stress has been associated with increased risk of premature birth, which is linked to higher rates of infant mortality and of physical and mental disorders, such as attention-deficit hyperactivity disorder and anxiety, among offspring.