When depressed mothers give birth to thriving babies

Shelves of evidence show the long-term, adverse consequences for an embryo of having a mother who is stressed or malnourished during pregnancy. For instance, there's medical data showing that underweight newborn babies are more at risk of heart diseases and other illnesses in adulthood.

According to the "thrifty phenotype" hypothesis, this is because the child is born with a body that's primed for malnutrition. When the baby instead encounters plentiful resources, its metabolism suffers as a result, leading to a long-term increased risk of stroke, heart disease and diabetes.

But what if the prenatal environment were a reliable predictor of the world that's to come? A surprising new study shows that adverse prenatal circumstances, in the form of having a depressed mother, are actually beneficial if that same context endures after birth. The finding is consistent with the "predictive-adaptive response model", which says that adversity in-utero can have adaptive advantages if adversity is also encountered after birth.

Curt Sandman and his team measured the depression levels of 221 healthy women during their pregnancy and for twelve months after their children were born. The babies were subsequently categorised into four groups. There were two "concordant" groups, for whom the environment was the same prenatally and post-natally, as in their mother was either depression-free in both phases or she had depression in both phases. And there were two "discrepant" groups, for whom the prenatal and postnatal environments were different, as in their mother had depression in one phase but not the other.

Here's the take-home finding: babies in the concordant groups exhibited superior scores on mental development at 3 and 6 months of age, and superior psychomotor development at 6 months, compared with the discrepant babies. Crucially, this was the case for both concordant groups. In other words, for babies whose mothers were depressed postnatally, it was those whose mothers were also depressed during pregnancy who fared better. This counterintuitive finding appears to contradict the received wisdom that adversity during pregnancy is only ever associated with adverse outcomes.

Zeroing in on the timings, it was specifically the consistency or not between a mother's depression state at 25 weeks' gestation and her depression state postnatally that had associations with the babies' developmental outcomes. This makes sense because past research has found mothers' depression at 25 weeks' gestation (as opposed to at other times) to be most strongly related with their emotional state postnatally. The researchers said it's as if the unborn child is "most sensitive to maternal signals of adversity when those signals are the most predictive of future outcomes."
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  Sandman, C., Davis, E., and Glynn, L. (2012). Prescient Human Fetuses Thrive. Psychological Science, 23 (1), 93-100 DOI: 10.1177/0956797611422073

Post written by Christian Jarrett for the BPS Research Digest.

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