Diagnoses of both a major depressive episode and posttraumatic stress disorder (PTSD) appear to be associated with a sizable increase in risk for preterm birth that seems to be independent of antidepressant and benzodiazepine medication use.

The study included a group of 2,654 pregnant women recruited before 17 weeks gestation. The authors looked for PTSD, major depressive episode, and the use of antidepressant and benzodiazepine medications. They measured preterm births, defined as birth before 37 weeks gestation.
Of the women, 129 (4.9 percent) had symptoms consistent with PTSD. Pregnant women with both PTSD and a major depressive episode had a four-fold increased risk of preterm birth. Each one-point increase on a scale measuring PTSD symptoms increased the risk for preterm birth by 1 percent to 2 percent. Women prescribed serotonin reuptake inhibitor and benzodiazepine medications had higher odds for preterm birth.
"The risk appears independent of antidepressant or benzodiazepine use and is not simply a function of mood or anxiety symptoms. Further exploration of the biological and genetic factors will help risk-stratify patients and illuminate the pathways leading to this risk."
Source-Eurekalert