Depression during pregnancy may increase the risk of giving birth early, a UK study suggests.
Depression during pregnancy is common
Mothers who were severely depressed gave birth earlier than those without depression, a small study shows.
The depressed mothers had significantly higher levels of a stress hormone which is known to initiate birth, an Institute of Psychiatry meeting heard.
Experts said depression during pregnancy is common and the findings should be looked at in a bigger study.
Dr Veronica O'Keane, perinatal psychiatrist at King's College London, measured amounts of corticotrophin-releasing hormone (CRH), in 25 women who had a diagnosis of major depression (but were not on medication) and 35 women without depression.
Levels of CRH - a hormone which is associated with stress but also naturally excreted by the placenta during pregnancy - were found to be higher in those with depression.
On average mothers with depression gave birth two days earlier - but three of the mothers in the depressed group had a premature birth (under 37 weeks) compared with none in the control group.
In a small subset of the babies at eight weeks, Dr O'Keane also found that those born to mothers who had depression had higher salivary levels of another stress hormone - cortisol - during routine vaccinations.
Previous research has shown that children born to mothers who had high levels of anxiety during pregnancy have higher levels of cortisol at 10 years old, indicating the stress gets passed on.
Dr O'Keane explained that CRH is needed for normal organ development in the foetus but the higher levels associated with depression could prompt premature delivery.
"In my opinion, depression is a major cause of pre-term birth because about in about 30% of cases there is no known cause but in that group a large proportion suffer from severe psychosocial stress."
Premature birth is the leading cause of neonatal death and infant mortality
The most serious problems occur in babies born before 32 weeks
Babies born prematurely can have various health problems including respiratory difficulties and neurological disorders
She added that depression was greatly under-recognised and under-treated during pregnancy.
"There is a myth that depression doesn't happen in pregnancy but postnatal depression probably started in pregnancy in about 50% of cases."
"I don't think women with a history of depression should discontinue antidepressants but they should go to a specialist," she said.
Professor Vivette Glover, professor of perinatal psychobiology at Imperial College London said the finding of an earlier birth was significant but it was important to note it was only a few days on average.
"We need to look at the relationship of CRH with cortisol - whether it's increasing cortisol which could do all sorts of things.
"It could be linked with smaller babies and brain development but there's a lot going on and we need to work out the link."
She said that depression during pregnancy was more common than postnatal depression.
"There's a balance but if I was severely depressed during pregnancy I would want to take antidepressants."
Professor Andrew Shennan, spokesperson for baby charity Tommy's said there was a lot of interest around CRH and premature birth.
"We have very little idea what causes pre-term birth and given how common depression is, it is certainly worth looking at this further."