Is a hormone behind postnatal depression?
“A ‘cuddle chemical’ released during love-making and breastfeeding could hold the key to preventing post-natal depression,” according to the Daily Mail. The newspaper said that research into the chemical oxytocin, which is released by a woman’s body during childbirth, has found that pregnant women with lower levels of the chemical are more likely to develop depression after birth.
The research in question was a small study featuring only 98 women that measured blood levels of oxytocin levels late in pregnancy and whether these were related to the risk of depressive symptoms after birth. However, levels of this chemical are known to fluctuate both during and after pregnancy, and the fact that oxytocin levels were measured just once undermines the study’s results. Also, depression was assessed using a questionaire rather than a formal diagnosis by a doctor. This leaves open the posibility that the women experienced fluctuations in mood rather than clinical depression.
Postnatal depression is thought to be associated with a number of risk factors, both psychological and physiological, including fluctuations in hormone levels. Larger, more robust studies are needed to confirm if oxytocin levels are a risk factor.
Where did the story come from?
The study was carried out by researchers from the University of Basel, Switzerland and the University of Trier in Germany.
The study was published in the peer-reviewed journal, Neuropsychopharmacology. It was funded by The Swiss National Science Foundation, the University of Basel, the Hoffmann-La Roche pharmaceutical corporation and the Basel Scientific Society.
The study was reported uncritically by both the Daily Mail and The Daily Telegraph. The Mail’s headline that a ‘cuddle chemical pill’ could prevent postnatal depression was overly optimistic and implied that research in this area was more advanced than it actually was.
The Mail also incorrectly reported that researchers looked at whether a shortage of the chemical was linked to ‘trouble in bonding’ between mother and child. However, the newspaper’s report did include the views of an independent expert and pointed out that oxytocin is used in hospitals to induce labour.
What kind of research was this?
This was a cohort study that aimed to find out if there was any association between blood levels of oxytocin in pregnancy and the development of postnatal depression. The researchers highlight that the condition affects up to 19% of new mothers and can have adverse effects on the mother and child relationship. It is thought to be linked to both physiological and psychological factors, including hormonal changes during and after pregnancy.
One possible factor, the researchers say, is the presence of the chemical oxytocin, produced by the pituitary gland and released in the brain. Oxytocin causes uterine contractions during labour and stimulates the flow of milk for breastfeeding. The researchers say animal studies have indicated that it also has a major role in enhancing the mother and infant bond. They hypothesise that lower oxytocin levels during pregnancy could result in ‘impaired adaptation to motherhood’ - a major risk factor for the development of postnatal depression. Synthetic oxytocin is already used to induce labour but is injected rather than given as a pill.
It is important to point out that the study did not look at any oxytocin-based treatment for postnatal depression. While reports discussed a ‘cuddle chemical pill’, the research tested no such drug. The study only measured the naturally occurring oxytocin levels in pregnant women to see if they were associated with the development of postnatal depression.
What did the research involve?
The researchers recruited 100 healthy pregnant women between weeks 21 and 32 of gestation (pregnancy normally lasts from 37 to 42 weeks). After screening for factors such as current mental illness, medical complications and signs of fetal malformation, 98 of the women were found to be eligible for the study. Researchers took blood samples from the women between weeks 30 and 34 of pregnancy, which were analysed for blood levels of oxytocin.
Participants were also interviewed to assess any recent or current or lifetime depression and anxiety, and given a standardised questionnaire to gather general information about their background and lifestyle.
During the third trimester of pregnancy the women were given questionnaires to assess their depressive symptoms according to a scale that is normally used after delivery to assess existing depression or the risk of developing postnatal depression. This scale, the Edinburgh Postnatal Depression Scale (EPDS), has 10 questions dealing with typical symptoms of postnatal depression, with answers given using a four-point scale. The same questionnaire was administered again within two weeks of delivery.
The researchers divided the pregnant women into two groups based on their postnatal scores:
- women with postnatal scores of 10 or more were regarded as being at risk of developing postnatal depression
- women with scores of less than 10 were regarded as not being at risk of developing postnatal depression
The researchers analysed their data using validated statistical methods. They controlled their results for symptoms of depression before birth, and other factors that might have affected mood, such as birth outcomes and social and economic background.
What were the basic results?
The researchers found that levels of oxytocin in mid-pregnancy ‘significantly predicted’ symptoms of postnatal depression two weeks after birth, with the at-risk group characterised by lower oxytocin levels.
Of the 100 women recruited, 73 had complete data and could be included in the analysis. Some 14 women, representing about 20% of the total sample, were found to be at risk of postnatal depression, as measured by the Edinburgh questionnaire.
Blood oxytocin levels ranged from 14.39-245.71pg/ml, with three women having levels above 200pg/ml. The model they developed for prediction suggests that blood oxytocin levels significantly predicted postnatal depression symptoms after birth (p<0.05), although they were not associated depression scale scores during pregnancy.
How did the researchers interpret the results?
The researchers say that those women who developed depressive symptoms in the two weeks after their delivery had lower blood levels of oxytocin during pregnancy than those who did not develop depressive symptoms. This association persisted after adjusting for depressive symptoms during pregnancy.
The authors say this finding is in line with previous studies that have looked at the link between oxytocin levels and maternal bonding behaviour, and that it is possible that low levels of oxytocin may cause postnatal depression. They suggest that future studies should look at whether modifying oxytocin levels in mid-pregnancy can help prevent postnatal depression.
Conclusion
As the authors note, this small study had a number of limitations.
- Only one sample of oxytocin was taken. Levels of the chemical are known to fluctuate both during and immediately after pregnancy, so relying on one sample for blood levels undermines the results.
- The sample consisted of women with medium-to-high socioeconomic status, so we cannot assume that the results would be the same for women from other backgrounds.
- The symptoms of postnatal depression were assessed by questionnaire, rather than by a standardised interview and a medical diagnosis of postnatal depression was not verified.
- There is still some debate as to whether the questionnaire used in this study can accurately assess postnatal depression.
- The questionnaire may have identified short-term mood fluctuations that many women experience immediately after giving birth and not the longer-term problem of postnatal depression. A formal diagnosis of postnatal depression requires symptoms to be present for at least two weeks
Far larger studies looking at the possible association between oxytocin levels and diagnosed postnatal depression are required. These need to look at levels of the chemical at different times during pregnancy and after birth, as well as assessing whether any symptoms of depression would constitute medically diagnosed postnatal depression.
