Study author Dr. Samantha Salvesen Adams initially thought her team would find the prolonged labor could be explained by other factors - women who feared birth the most were first time mothers, who are known to have longer labors anyway, or obstetric interventions like epidurals. But when those factors were taken into consideration, the difference in time between the fearless and the fearful was still 47 minutes.
"Mental stress is associated with physiological arousal and release of stress hormones," Adams wrote in an e-mail. "During labour, high levels of stress hormones may weaken uterine [contractions]."
In other words, the adrenaline released when a body is stressed stops the oxytocin hormone production that makes a woman's uterus contract, slowing labor. It's a natural, biological response to fear, [Dr. Stuart] Fischbein said.
Image: Pregnant woman with clock, via Shutterstock.