Babies born to mothers with bipolar disorder are at increased risk of preterm birth (before 37 weeks) a study published today on bmj.com suggests.

Infants of mothers with untreated bipolar disorder are also at increased risks of outcomes related to fetal growth restriction.

Bipolar disorder (sometimes called manic depression) is a serious, long term condition involving extreme mood swings. Treatment with mood stabilising drugs like lithium, anticonvulsants or antipsychotics can help keep mood within normal limits.

Previous studies have suggested that these drugs may be linked to pregnancy and birth complications, whereas little is known about adverse outcomes in untreated women with bipolar disorder.

So researchers from Uppsala University and the Karolinska Institutet in Sweden investigated the risks of adverse pregnancy and birth outcomes in both treated and untreated women with bipolar disorder.

Using data from three national health registers, they identified 320 mothers with treated bipolar disorder and 554 untreated mothers. Treated and untreated women were compared with all other women giving birth (331,263) between 1 July 2005 and 31 December 2009. Results were adjusted for several factors including maternal age, weight, smoking status, cohabitation and a diagnosis of alcohol or substance use disorder.

Mothers with bipolar disorder were more often smokers, overweight and alcohol or substance abusers than unaffected mothers.

Both treated and untreated mothers with bipolar disorder had increased risks of caesarean delivery, instrumental delivery (use of a vacuum or forceps), and a non-spontaneous start to delivery (120/320 or 37.5% of treated women, 171/554 or 30.9% of untreated women, 68 533/331 263 or 20.7% of other women). Treated and untreated mothers also had 50% increased risks of preterm birth compared with unaffected mothers (26/320 or 8.1% of treated women, 42/554 or 7.6% of untreated women, 15 785/331 263 or 4.8% of other women).

Untreated mothers were also more likely to give birth to a baby with a small head (microcephaly) and with episodes of low blood sugar levels (neonatal hypoglycaemia) compared with unaffected mothers.

The researchers conclude that "mood-stabilising treatment is probably not the sole reason for the increased risk of adverse pregnancy and birth outcomes previously observed in mothers with bipolar disorder." They also suggest that the role of treatment is still unclear as the overall outcomes "generally did not support a significant difference between untreated and treated" mothers.

In an accompanying editorial, mental health expert, Dr Salvatore Gentile says the question is not "to treat or not to treat?" but "how to treat optimally?" Because no drug is without risks, clinicians cannot hope to identify a "safe choice," but merely a "less harmful" one.

He adds that patients must be properly counselled about the risks of treatment versus the risks associated with the untreated psychiatric disorder, and doctors should "encourage and facilitate social integration, especially for women from disadvantaged social groups and those who are isolated."