Many people may associate post-traumatic stress disorder (PTSD) with veterans of the military, and for good reason, too. Many soldiers who have come back from the frontlines of Iraq and Afghanistan have gone on to develop the severe anxiety disorder. But what many people don’t know is that PTSD affects women more, and being in the military isn’t the only situation in which PTSD can develop. Now, a new study has found that the effects of PTSD may extend further than previously believed, causing any woman who wishes to have a baby to give birth prematurely.

The study was conducted by researchers at the Yale School of Medicine, and involved 2,654 pregnant women who signed on to the study before 17 weeks of pregnancy. All of them were given questionnaires asking about symptoms of PTSD and major depressive disorder; whether they were taking antidepressant medications; and whether they’d experienced any traumatic events.

The researchers found that 129 women had symptoms in line with PTSD. When it came to premature birth, those who had these symptoms, as well as those similar to major depressive disorder, were four time as likely to give birth prematurely — defined as before 37 weeks of pregnancy. For each one-point increase on a PTSD-measuring scale, their chances of preterm birth rose by one to two percent, and those who were taking antidepressant medications were even more likely to give birth prematurely.

Women are twice as likely to develop PTSD as men, according to the Department of Veteran’s Affairs, and although there are many reasons, from war and death to a car accident, the one major reason they develop it more is because of sexual assault. Their chances then increase with other subsequent stressful events, faulty social support systems, and mental health problems.

When it finally does develop, it causes long-lasting effects on the person’s psyche, leading to nightmares, terrifying flashbacks, and uncontrollable scary thoughts. Women are also more likely to be jumpy, have more trouble managing emotions, and spend more time avoiding situations that remind them of the incident.

The researchers said that further studies into the biological and genetic factors of this finding will help determine causality. But they note that another study, such as one on women with PTSD from the September 11th attacks, found that babies were much smaller than normal. Premature birth has been linked to a range of health complications, including breathing problems, feeding difficulties, cerebral palsy, and hearing impairment.

Source: Yonkers K, Smith M, Forray A, et al. PTSD, Major Depressive Episode Appears to Increase Risk of Preterm Birth. JAMA Psychiatry. 2014.