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Cohort study
The possible effects of depressive symptoms on risk of preterm birth are clouded by lack of control over confounding factors
  1. Kimberly A Yonkers
  1. Yale University School of Medicine, New Haven, Connecticut, USA
  1. Correspondence to: Kimberly A Yonkers
    Yale University School of Medicine, 142 Temple Street, New Haven, CT 06896, USA; kimberly.yonkers{at}yale.edu

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Context

Depressive symptoms have been associated with risk of preterm birth (PTB).1 Straub and colleagues sought to explore whether an elevated score on the Edinburgh Postnatal Depression Scale (EPDS) is associated with adverse birth outcomes, including PTB.

Methods

The authors present results from a ‘universal’ screening project that enrolled 14 175 women who received prenatal care through the NorthShore University Health System. Approximately 50% of women receiving prenatal care were screened. Barriers to inclusion were participant refusal and administrative issues, but PTB rates were similar in screened and non-screened subgroups. Screening occurred between 24 and 28 weeks gestation; the method (eg, self-report or clinician-administered) was not described. A screen was considered positive if the score was >12, or if the woman endorsed suicidal thoughts. Screening results were linked with electronic medical records, and birth outcome data were extracted. The authors used multivariable logistic regression to model risk of birth <37 weeks (PTB), <34 weeks, <32 weeks, <28 weeks or delivery of a small for gestational age (SGA) infant. The analytical approach included possible confounders of race, age, history of prior PTB and insurance status. The use of antidepressant medications, tobacco or other licit and illicit substances, was not included in models.

Findings

The rate of PTB was 13.9% in women with as compared to 10.3% in women without elevated depressive symptoms. The adjusted OR for PTB was 1.3 (95% CI 1.09 to 1.35). The risk was slightly higher when only singleton pregnancies were included (1.7, 95% CI 1.38 to 1.99). Exposure to depressive symptoms also increased the risk of earlier PTB and SGA (6.6% vs 5.1%; p<0.001).

Commentary

This study included a large and generalisable cohort of pregnant women. However, there are limitations. First, an elevated score on the EPDS does not necessarily indicate a depressive disorder but can indicate an anxiety disorder, a substance use disorder or any emotional condition of high stress.2 The use of various licit and illicit substances in pregnancy is associated with adverse birth outcomes and may be a more potent risk factor for adverse birth outcomes than depression or stress.3 Importantly, problems with poor health habits, including the use of cigarettes, alcohol and illicit substances, are greater among women who have high levels of depressive symptoms as compared with those with fewer depressive symptoms.4 Second, elevated scores on the EPDS are also found among individuals who suffer from domestic violence and post-traumatic stress disorder, which are also associated with adverse birth outcomes.5 Third, the authors do not address the possible effects of antidepressant medication on PTB, despite the fact that antidepressant use has been found to be a risk factor for this outcome.6 In short, the very modest increase in risk for PTB (between 9% and 35%) could be the result of confounding due to these other risk factors.

Prior literature has found mixed results with regard to an association between depressive symptoms and PTB. A recent meta-analysis found an association (1.30 (1)=1.19–1.61) between depression and PTB that was small and similar to the study under discussion. Many studies contributing to the meta-analysis were similarly unable to control for the use of illicit or licit substances, or for other psychosocial conditions such as violence and trauma.

Apart from the unsettled relationship between depression and PTB, there are implications resulting from this study and the literature. Elevated scores in psychiatric screening tests of pregnant women indicate distress and are common. They should trigger a complete psychiatric assessment, as was done in the study under discussion. Whether a mother delivers preterm or not, a healthy mother is best for her and for her children.

References

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Footnotes

  • Competing interests KAY's institution has received research grants from NIMH, NIDA and study medication from Pfizer. KAY has also received royalties from UptoDate.

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