Friday June 27 2008
Postnatal depression is common
“Children born to women who are depressed during pregnancy are more likely to suffer significant delays in their development,” The Daily Mail reported. It said a study found that the risk of poor mental and physical development increased by up to 34%, and when mothers had postnatal depression too, the risk rose to 50%.
Previous studies have associated postnatal depression with children’s development, and this study investigated whether there is also a link with depression during pregnancy. Although the findings indicate a link, the relationship between depression and developmental delay is complex. This study cannot prove conclusively that depression at any time is the cause for developmental delay, which may have several medical, genetic and social/environmental causes. The children were also examined only once at 18 months, and apparent developmental delay at this age might not reflect their later development.
Mothers who develop depression during or after pregnancy should not be unduly concerned that they are possibly delaying their child’s development. This study highlights the prevalence of depression during pregnancy and early motherhood; it also highlights the need for health carers to be alert for signs of depression, and to ensure that mothers and their babies receive the full care and support they need.
Where did the story come from?
The research was carried out by Dr T Deave from the Centre for Child and Adolescent Health, University of the West of England, and colleagues from the Departments of Social Medicine, Academic Unit of Psychiatry, and Centre for Child and Adolescent Health, University of Bristol. The study was supported by the UK Medical Research Council, the Wellcome Trust and the University of Bristol, and the lead researcher received a Higher Education Funding Council for England postdoctoral fellowship from the University of the West of England.
The study was published in the peer-reviewed medical journal British Journal of Obstetrics and Gynaecology.
What kind of scientific study was this?
In this prospective cohort study, the researchers aimed to examine the associations between maternal depression during pregnancy and child development at 18 months of age.
This study used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) – which has been following a large sample of the community from the county of Avon, West England. The study followed mothers during and after pregnancy and their children. It included all women who were due to give birth between April 1991 and December 1992 – a total of 14,062 live births. Socioeconomic information, family details, and other data (not specifically outlined in this report) were collected at 18 and 32 weeks of pregnancy.
The women completed a validated 10-item questionnaire (the Edinburgh Postnatal Depression Scale - EPDS) at 18 and 32 weeks of their pregnancies. The questionnaire is normally used to assess postnatal depression, and the women rated their feelings over the past seven days, giving a total score between 0 and 30. Higher scores on the EPDS indicate greater symptoms. Women completed the questionnaire again eight weeks and then eight months after the birth. Only women with singleton births were included in the study.
The researchers grouped women into three antenatal depression groups: those who had scores below the EPDS cut-off for depression, those who had scores at or above the cut-off on one occasion (at either 18 or 32 weeks of pregnancy), and those with scores at or above the cut-off on both occasions. Three different cut-offs were used to analyse the data: scores 9 or 10, 12 or 13 (the standard cutoff), and scores 14 or 15. The researchers say that they used the different cut-offs to reflect the continuous nature of the data.
Developmental delay in the children was assessed using a modified version of the Denver Developmental Screening Test (DDST), which their parents completed. The DDST is a screening questionnaire that identifies cognitive and behavioural problems in pre-school children. The test examines children according to what is normal for their age. The more items failed increases the likelihood that they have developmental delay. Children were considered to have developmental delay if they failed two or more items in the questionnaire.
Statistical tests were used to examine the relationship between depression, developmental delay and other confounding factors, including maternal anxiety, previous depression, depression and anxiety in the father, gender and ethnicity of the child, feeding patterns, demographic details, and life events in the previous year and postnatally.
What were the results of the study?
The researchers had complete antenatal data available for 11,098 women of whom 44% were expecting their first child. Women for whom there was incomplete antenatal data were excluded. These had a higher proportion of single women, women with unemployed partners and women whose education had reached O Level or equivalent qualifications. Of the women with complete antenatal data, 9,244 also had complete developmental data for their child at 18 months.
Using the standard 12/13 score cut-off on the EPDS, 14% of women in the sample had depression during pregnancy (at either or both 18 and 32 weeks) but not postnatally. Only 1.4% of women had depression both during pregnancy and postnatally, and 4.8% of women were depressed postnatally, but not during pregnancy. At 18 months, 9% of children had developmental delay.
When the lower threshold for defining antenatal depression (the 9/10 cut-off) was used, women with depression at both time points (18 and 32 weeks of pregnancy) were significantly more likely to have a child with developmental delay compared to women without depression during pregnancy (a risk increase of 34%) after other potential confounding factors were taken into account. These included maternal age, smoking during the first 12 weeks of pregnancy, and life events at eight months. Using the standard 12/13 cut-off, the risk increase was still significant, at 50%. However, results just lost significance when the 14/15 cut-off was used. There was no significant link between antenatal depression at only one time point (using any of the three cut-offs) and developmental delay.
When women’s postnatal depression was taken into account, the increase in risk of their child having developmental delay if the mother had antenatal depression at both 18 and 32 weeks was reduced. When the 10/11 or 12/13 cut-off were used, the results were only just significant. Results were non-significant using the 14/15 cut-off and, again, were non-significant for women who had antenatal depression at only one time point.
What interpretations did the researchers draw from these results?
The researchers said that their findings highlight the importance of depression during pregnancy. They conclude that some of the effects on childhood development that have previously been attributed to postnatal depression may in part be caused by depression during pregnancy.
What does the NHS Knowledge Service make of this study?
This extensive study highlights the prevalence of depression during pregnancy. It also raises the possibility of associations with developmental delay at 18 months. A few points to consider when interpreting this study are:
- It is not possible to conclude that either antenatal or postnatal depression is the cause of developmental delay in children. As the results have shown, there is a complex relationship between the two, with the significance of the link susceptible to change if more than one time point during the pregnancy or after the birth is taken into account.
- Developmental delay may have many different causes, and these could be medical, genetic or social/environmental. Although many of these were considered by the authors, not all were taken into account, such as illnesses or mother-child interaction. It is also unclear how those factors that were adjusted for were examined or taken into account, e.g. maternal life events at eight months.
- Considering the mother’s depression on only two occasions before and after they gave birth may not be representative of the mother’s mental health during the whole period. It is also unclear whether low mood at any one time may have more of a significant effect upon the developing baby than others.
- The child was only examined at 18 months, and apparent developmental delay at this age may not correlate with any problems in later childhood and adolescence when the child may have ‘caught up’ with their peers.
- As the researchers acknowledge, low mood in the mother may have also affected their completion of the childhood developmental questionnaire and biased their assessment of their child on the DDST.
- The results of those women and children who were excluded because they gave incomplete pre- and postnatal data may have affected the results, e.g. depressed women may have been less likely to choose to participate in postnatal follow-up.
- The total number of women with depression at any time in this study was low, and may therefore affect the ability of the study to detect significant relationships between depression and developmental delay compared to if the study had followed up the children of a large number of women with pre or postnatal depression.
- Of the children sampled, 98% were white British, and this may limit how representative the findings are to other ethnic groups or cultures.
Depression, postnatal and during pregnancy, is often unexpected, unavoidable and troubling for both the mother and family. Mothers who are affected should not be unduly concerned that they are possibly delaying their child’s development.
Perhaps most importantly, this study highlights the prevalence of depression during the transition to motherhood. Health carers need to be alert for signs of depression, and to ensure that mothers and their babies receive the full care and support they need.