If you’re trying to get pregnant and want to have a boy, science says you may need to practice relaxation.
Researchers at Columbia University in New York have found that mothers-to-be who are stressed are more likely to have daughters.
The findings don’t suggest that the pressures of everyday life can change a baby’s sex in the womb, but rather that anxious women are less likely to have a successful pregnancy with a boy because male foetuses are less robust.
The study was carried out by researchers at the university’s Vagelos College of Physicians and Surgeons, and collected data for 27 indicators of stress in 187 healthy pregnant women aged 18 to 45. Researchers made use of questionnaires, diaries, and physical assessments throughout the pregnancies of participating members.
They divided the women into three groups – those who have a healthy pregnancy with no stress, those who show signs of physical stress and those with signs of psychological stress.
Of the sample group, one in six women were psychologically stressed, reporting negative feelings during their day, feeling overwhelmed and out of control, or indicating mild to moderate depression or anxiety.
A similar number of women showed signs of physical stress, such as higher blood pressure and a tendency to consume more calories, which is suggestive of comfort eating.
Among the moms-to-be who were physically stressed, less than a third (31%) gave birth to a boy, a ratio of nine girls to every four boys.
The study’s findings were presented even more clearly among women coping with psychological stressors, with only 40% giving birth to a boy – a ratio of two baby girls to every boy.
According to study leader, Catherine Monk, male foetuses are less likely to “survive in suboptimal conditions” for an abundance of biological reasons.
For example, a 2010 study proved that male foetuses grow more quickly in the womb and therefore are more at risk of becoming undernourished and being born prematurely.
Monk claims that the impact of stress on male births can be seen on a population level after catastrophic events.
“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,” she says.
According to a study, 12% more male babies were lost in September 2001 after the 20th week of pregnancy than expected.
“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 were published online in the Proceedings of the National Academy of Sciences journal (PNAS).
However, the negative effect of stress appeared to be offset by social support from friends and family. For example, they found that 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,” Monk says.
“But while our study was small, the results suggest enhancing social support is potentially an effective target for clinical intervention.”