Depression can double risk of premature birth, reports The Daily Telegraph. A study has found that severely depressed women run twice the risk of their baby being born early, while those of milder depression had a 60% increased risk. Of the entire group of pregnant women, 41% had depressive symptoms at their 10th week of pregnancy, the newspaper says.

The story is based on a study which followed 791 pregnant women, assessing them for depression and then seeing how this related to the risk of premature birth. The study found that risk was doubled in women with depression scores that indicated severe depression. The research has some limitations, as depressive symptoms were assessed on only one occasion, and some other medical risk factors for premature birth were not taken into account. Nevertheless, the study highlights the need to consider depression in the antenatal period, as well as the postnatal, and to ensure that all women receive the full care and support they require.

Where did the story come from?

De-Kun Li and colleagues of Kaiser Foundation Research Institute, Kaiser Permanente, California, carried out this research. The study was funded by the California Public Health Foundation. It was published in the peer-reviewed medical journal, Human Reproduction.

What kind of scientific study was this?

This was a cohort study in which the authors aimed to investigate the prevalence of prenatal depression and its impact on one of the outcomes of pregnancy.

The researchers recruited women in early pregnancy from the Kaiser Permanente Medical Care Program (KPMCP) who were English-speaking, living in the San Francisco area and who planned to carry their pregnancy to term. Of all the eligible women, 1,063 were recruited (those who did not take part gave reasons such as too stressful or too busy).

The women were interviewed at week 10 of their pregnancy, and their levels of depression were assessed using the Center for Epidemiological Study Depression Scale (CESD). The CESD is a 20-item questionnaire which does not diagnose clinical depression but instead measures the level of depressive symptoms, and has been widely used for study purposes. The scale has a maximum score of 60, and higher scores indicate greater levels of depressive symptoms. The researchers used a cut-off score of 16 or more to indicate significant depressive symptoms and 22 or more for severe depressive symptoms. They also collected information on risk factors for adverse pregnancy outcomes, by taking a medical and reproductive history, and covering sociodemographic issues.

The researchers collected information about pregnancy outcomes by searching the KPMCP databases or reviewing medical records or contacting the women personally if the information was otherwise unavailable. They excluded women who miscarried before 20 weeks of pregnancy, those with incomplete CESD questionnaires, those with unreliable information about pregnancy dates, and those who delivered extremely prematurely, before 33 weeks of pregnancy. This left them with a final study group of 791 women. They looked at the number of women who delivered prematurely (at less than 37 weeks), and assessed whether depressive symptoms were a risk factor for this. They also looked at other potential risk factors, including stressful life events and social and personal characteristics.

What were the results of the study?

At 10 weeks of pregnancy, 41.2% of women had CESD scores of 16 or more (significant depressive symptoms) and 21.7% had CESD scores of 22 or more (severe symptoms). Compared with women who did not have symptoms (CESD score of less than 16), those with significant symptoms were more likely to be younger, less educated, have a lower income, be unmarried or of African-American origin. They were also more likely not to have planned their pregnancy, not to use vitamin supplements, to have had vomiting during their pregnancy, to have had three or more prior pregnancies, and to have a history of fertility problems.

About 4% of women without depressive symptoms delivered prematurely (before 37 weeks), compared with 5.8% of those with significant depressive symptoms and 9.3% of those with severe depressive symptoms. After adjusting for the differences between maternal characteristics, the researchers found a relationship between increased risk of premature birth with increased CESD score. Compared with those without symptoms, women with severe symptoms (CESD score of 22 or more) had more than double the risk for premature delivery (hazard ratio HR 2.2, 95% confidence interval CI 1.1 to 4.7). Although there was an increased risk of premature birth for those with CESD scores of 16-21, this increase was not statistically significant (HR 1.6, 95% CI 0.7 to 3.6).

When they looked to see if other characteristics affected the association between depression and premature delivery, they found that the risk of premature birth tended to be greater among women with depressive symptoms who also had lower education, a number of previous pregnancies, subfertility or a history of stressful life events.

What interpretations did the researchers draw from these results?

The researchers conclude that a large proportion of pregnant women in their cohort had significant or severe depressive symptoms in early pregnancy, and that they are at increased risk of premature delivery. Other social and reproductive risk factors may exacerbate this effect.

What does the NHS Knowledge Service make of this study?

This relatively large and well-conducted study has demonstrated an increased risk of premature delivery in women who have severe depressive symptoms in early pregnancy, and has given an indication of the prevalence of depressive symptoms in early pregnancy. However, the study does have some limitations.

• Although widely used for study purposes and said to be a good indicator for clinical diagnosis, the CESD questionnaire does not give a clinical diagnosis of depression, and therefore the prevalence of mild-to-severe depression and the associated risk figures for premature birth may have been different if a clinical diagnosis had been used instead. In particular, the high 40% prevalence of significant depression at 10 weeks of pregnancy may be slightly overestimated compared with clinical scales.
• The women were assessed for depressive symptoms at 10 weeks only, therefore the risk and prevalence figures only relate to a single assessment in early pregnancy. Assessments in mid or late pregnancy may have given different results.
• Although the researchers excluded those women who delivered before 33 weeks (whose premature delivery was almost certainly related to maternal or foetal complications), there are a wide number of risk factors associated with prematurity that have not been accounted for in the analyses, e.g. multiple births, pre-eclampsia, infection, uterine/cervical abnormalities, etc.
• Although a large sample, a high proportion of those who were eligible chose not to participate in the study. One of the reasons given was that it was too stressful. It is possible that a number of non-participants had some degree of antenatal depression or related disorders, and this may have altered outcomes had it been possible to include them.

The possible reasons for the relationship between depression and premature delivery shown in this study remain unclear at this stage. However, this study highlights the need to consider depression during the antenatal period, as well as the postnatal, and to ensure that all women receive the full care and support that they require.