Marital instability affects brain development in babies

Babies notice more than we think. A study published in 2011 in the journal Child Development found that strain in a couple's relationship when their baby was nine months old predicted sleep problems — trouble falling asleep and staying asleep — when that child was eighteen months old.

The research, led by Anne Mannering and Gordon Harold with colleagues at the Oregon Social Learning Center, the University of Leicester, Penn State, and several other institutions, followed 357 families. The parents were interviewed twice, at nine months and at eighteen months, about their relationship — including whether they had seriously considered divorce — and about their child's sleep.

The clever part of the design was the sample: all the children had been adopted at birth. That removed one of the usual objections to this kind of research, which is that the same genes might make both the parents prone to conflict and the child prone to poor sleep. With no shared genes between parents and children, whatever link appeared was far more likely to run through the home environment.

And the link ran in only one direction. Marital instability at nine months predicted sleep problems at eighteen months — but sleep problems at nine months did not predict later marital instability. The effect, in other words, flowed from the couple's relationship to the child, not the reverse.

The researchers' reading was that a baby absorbs the emotional climate of the home. Infancy is when sleep patterns are becoming regulated, and regulated sleep matters for healthy brain and physical development. A tense household — raised voices, cold silences, the ambient stress of a marriage in trouble — can keep an infant's arousal system switched on at exactly the stage when it needs to learn to switch off.

None of this means every bad week in a marriage damages a baby, or that parents should perform serenity they don't feel. The study measured sustained instability, not ordinary arguments. But it does suggest that the atmosphere between parents is not background noise to an infant — it is part of the environment the infant's developing brain is listening to.

The full study is freely available at the US National Library of Medicine.

This article describes published research and is general information, not medical advice. If your baby has persistent sleep problems, talk to your pediatrician.