Thursday February 14 2008
Is postnatal depression linked to boys?
Having a baby boy could mean the mother is at greater risk of postnatal depression after childbirth, says The Daily Telegraph today. A French study shows that “three-quarters of women who were diagnosed with severe postnatal depression, had sons”, the newspaper adds. The Daily Mail article says that women are “more likely to experience a poorer quality of life in the months after the arrival”.
The newspaper story is based on a small study investigating a link between postnatal health and gender. Among the 17 women identified with severe depression, 13 had boys and four had girls. However, the study provides limited information on the statistical significance of this and, given the small numbers of women involved, it possible that the difference occurred by chance or because of other systematic differences in the selection of the women involved.
Where did the story come from?
Professor Claude de Tychey from the University of Nancy in France, and colleagues, carried out this research. It is not clear how the study was funded. It was published in the medical journal: Journal of Clinical Nursing.
What kind of scientific study was this?
This was a cross-sectional study carried out in the postnatal period between four and eight weeks after birth. It is an early analysis of an ongoing study that will look at the long-term postnatal health of women.
The researchers studied a sample of 181 women by getting them to complete two standard questionnaires (the GHQ12 and the Edinburgh postnatal depression score [EDPS]), which are used to identify depression, and another questionnaire (SF36) that measures self-reported quality of life on a scale of zero (worst quality of life) to 100 (best quality of life).
The EPDS scale scores women’s responses to 10 statements (between zero and three), such as, “I have been able to laugh and see the funny side of things.” The total score possible is 30, and this indicates the most severe depression. The researchers in this study defined severe depression as women scoring 12 or more on this scale, and those scoring less than eight as having no depression. Women who scored between eight and 12 were classified as having mild depression. The researchers looked at the women in each of these groups and discovered that there was a difference in the number of boys born to the most severely depressed group. They then analysed the data once this trend had been discovered.
What were the results of the study?
The researchers reported that post-natal depression had a negative influence on general quality of life scores. They also report that having a boy significantly reduces quality of life irrespective of whether the mother was depressed. They report that the increased number of boys in the severely depressed group of women (13) compared with the number of girls (four) as significant.
What interpretations did the researchers draw from these results?
The researchers conclude that: “In view of the degree to which life quality is impaired and even greatly reduced in the case of the birth of a boy, we wish to stress the importance, in clinical practice, of setting a preventive programme as early as possible and of evaluating its effects. This programme should be aimed at facilitating the construction of parenting skills so as to confront this major public health problem and to exhaustively explore the reasons for which life quality seems to become more of a problem for mothers when their newborn child is a boy.”
What does the NHS Knowledge Service make of this study?
The conclusions of this study are based on a small number of cases of severe depression discovered by chance. There are limitations to the way the researchers have interpreted the results and the design of the study. It is not possible to be confident that the effect shown in this sample of women is real.
- It is not clear how the 181 women were selected for this study and how many were asked but declined to participate. Any differences in recruitment may have introduced a bias towards one sex in the results.
- The cross-sectional study was originally designed to look at the prevalence of depression and quality of life findings in the post-natal period, and not to look at whether there was a difference between mothers of boys and mothers of girls.
- The cut-off for severe depression was not decided in advance and so it is possible that choosing a threshold for the diagnosis of severe depression, which produces the largest sex difference, has led to the trend seen.
- For those women with mild depression a reverse trend was observed where girl babies were more common. It is unlikely that if there was any causal effect of sex on the depression score, that it would reverse across the spectrum of depression.
- The result reported for the sex difference of babies born to mothers who go on to develop severe depression is barely significant (p=0.04) and confidence intervals are not given. This p value suggests that if this study was repeated many times, a similar or greater difference than that expected would occur by chance 4% of the time.
It is reasonable to be suspicious of results from small trials that come as a surprise to the researchers. In particular, calling for the introduction of targeted interventions to address the issue of why depression and poorer quality of life may be more common in mothers of boys, seems unwise, without further studies to confirm what might be a chance finding.