Mothers with a mental illness are more likely to give birth too early, according to research.
But the risk of preterm birth can also be affected by a father’s mental health.
In our new study published in the journal PLOS Medicine, we found that fathers’ mental illness increases the risk of preterm birth and that the risk is even greater when both parents are affected.
Preterm birth refers to delivery before 37 weeks of pregnancy, and is associated with a greater risk of negative health outcomes for the child. For example, babies born preterm have higher rates of neurodevelopmental conditions such as autism spectrum disorder. The earlier the baby is born, the higher the risk of complications.
Growing evidence suggests that risks of adverse health outcomes are elevated not only for infants born preterm, but also for infants born “early term” (at 37 to 38 weeks of pregnancy).
1.5 million babies
We included data on 1.5 million infants born in Sweden between 1997 and 2016. We obtained information about the parents’ mental health from the National Patient Register, which records all psychiatric diagnoses by clinical specialists in Sweden. We ascertained length of pregnancies in weeks (gestational age) from the Medical Birth Register where all Swedish births are recorded.
Some 15% of the infants had at least one parent with a mental health disorder. Children of parents with mental illness tended to have a shorter gestational age.
Compared with children where neither parent had a mental illness, infants whose fathers but not mothers had a mental illness had a 12% increased risk of being born preterm, whereas the risk increased by 31% if only the mother had a mental illness. If both parents did, the risk increased by 52%.
In absolute numbers, for parents without mental illness, one in 17 children were born preterm. A diagnosis in fathers increased the risk to one in 16, in mothers to one in 14, and in both parents to one in 12 children. We observed a similar pattern of risk for infants born at early term.
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Of all the mental health conditions we looked at, stress-related disorders, such as post-traumatic stress disorder, were associated with the highest risk of preterm birth. The risk increased by 23% if the father had a stress-related disorder, 47% if the mother suffered from a stress-related disorder, and 90% if both parents had a diagnosis, compared with children where neither parent had a stress-related disorder.
The risk was also increased if parents had multiple different psychiatric disorders. For example, children of a mother with depression were 25% more likely to be born preterm compared to children of a mother without a psychiatric disorder. When the mother had depression and schizophrenia at the same time, the risk increased by 39%. If the mother had depression, schizophrenia and anxiety disorder, the risk increased by 65%.
Similar patterns were seen when the father had multiple disorders.
Why the link?
Previous studies have linked mental illness in mothers with an increased risk of preterm birth, but we’ve known much less about the father’s role in this regard. Our study demonstrates the significance of a father’s mental illness in the risk of preterm birth.
The underlying mechanism is likely to be complex – we can only really speculate on what is behind these trends.
Maternal stress has been linked to higher levels of stress hormones, which may induce premature contractions. Suffering from a mental illness, or having a partner with a mental illness, will probably be a source of stress for an expectant mother.
Research suggests that a father’s support during pregnancy can moderate the effects of maternal stress. In one study, women with chronic stress who had better support from the baby’s father (including emotional and financial support) had a lower risk of preterm delivery. When both parents have a mental illness, such support is probably more likely to be lacking.
Also, some social and environmental disadvantages that increase the risk of preterm birth, such as substance abuse, smoking, and low socioeconomic status, may cluster in families where one or both parents have a mental illness. These factors may play a role in the association between parental mental illness and preterm births.
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Roughly one in eight people in the world have a mental disorder. Future studies should examine whether additional social support and prenatal care for families with mental illness could lessen the risk of preterm birth, as well as the potential effects of psychiatric medications and treatments.