Stress In Early Pregnancy Can Lead To Shorter Pregnancies, More Pre-term Births And Fewer Baby Boys


Stress in the second and third months of pregnancy can shorten pregnancies, increase the risk of pre-term births and may affect the ratio of boys to girls being born ...

... women who experienced a severe quake ... during their second and third months of pregnancy had shorter pregnancies and were at higher risk of delivering pre-term (before 37 weeks gestation). The pregnancies of women exposed to the earthquake in the second month of pregnancy were on average 0.17 weeks (1.3 days) shorter than those in the unaffected areas of Chile. The pregnancies of those exposed in the third month were 0.27 weeks (1.9 days) shorter. Normally, about six in 100 women had a pre-term birth, but among women exposed to the earthquake in the third month of pregnancy, this rose by 3.4%, meaning more than nine women in 100 delivered their babies early.

The effect was most pronounced for female births; the probability of pre-term birth increased by 3.8% if exposure to the quake occurred in the third month, and 3.9% if it occurred in the second month. In contrast there was no statistically significant effect seen in male births.

As the stress of the earthquake had greater effect on pre-term births in girls rather than boys, the researchers had to make adjustments for this when calculating the effect of stress on the sex ratio: the ratio of male to female live births. They found that there was a decline in the sex ratio among those exposed to the earthquake in the third month of gestation of 5.8%.

... "Generally, there are more male than female live births. The ratio of male to female births is approximately 51:49 ... 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 ...

Previous research has suggested that in times of stress women are more likely to miscarry male foetuses because they grow larger than females and therefore require greater investment of resources by the mother; they may also be less robust than females and may not adapt 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," ... "In contrast, among female conceptions, stress exposure appears not to affect the viability of the conception but rather, the length of gestation."

... possible mechanisms to explain their findings could involve the placenta, which sets the duration of the pregnancy, and the effect of the stress hormone cortisol on the placenta's function ...

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