1. Women who had a term C-section in the second stage of labor were 6 times more likely to experience future preterm births than those who had a C-section in the first stage.
2. Women who had a vaginal delivery were more likely to have a future preterm birth compared with those who delivered by C-section.
Evidence Rating Level: 2 (Good)
Study Rundown: Preterm birth is a leading cause of neonatal mortality worldwide and remains a major public health concern in the United States. Infants born preterm (<37 weeks gestation versus) also face a host of health problems later in life, including cerebral palsy, developmental delay, behavioral problems, and even vision issues. Delivering a child preterm has even been associated with long-term heart problems for the mother. While there are a number of known risk factors, including smoking and alcohol use, poor nutrition, and IVF pregnancy, many women present without any risk factors. A prolonged second stage of labor (after the cervix is fully dilated >10cm) has been purported by some experts as a theoretical risk factor for future preterm births because of the cervical trauma that may occur. When the cervix is dilated for an extended period of time, cervical integrity may be disrupted, making it weaker in future pregnancies. While this theory is supported by experts and has been described in case reports, more rigorous testing is lacking. In the present study, rates of preterm births after cesarean deliveries at first and second stages of labor were compared with those after vaginal delivery.
Researchers found that women with a second stage cesarean delivery at term experienced higher rates of subsequent preterm deliveries than those who had a first stage cesarean delivery. This is the first study to specifically look at the effect of stage of labor when cesarean delivery was performed on risk of future preterm birth. One major limitation of this study is that it was a secondary analysis, so the initial study was not powered to detect future preterm birth. Additionally, rates of preterm birth were higher in the study population than in the general population (7.8% vs. ~5%), such that results may not be generalizable to a lower risk population. Future studies might replicate results using a multi-center design in a larger population.
Relevant Reading: Cesarean delivery outcomes after a prolonged second stage of labor
In-Depth [retrospective cohort]: In a secondary analysis of a large retrospective cohort study of women with 2 consecutive deliveries, researchers compared rates of spontaneous preterm birth in the second delivery among women whose first delivery ended in a vaginal birth (n = 721), first stage cesarean section (n = 129), or second stage cesarean section (n = 37).
Rates of future preterm births varied significantly between groups: 7.8% for vaginal delivery, 2.3% for first stage cesarean and 13.5% for second stage cesarean (p = 0.03). Women who had a second stage cesarean were more likely to experience a future preterm birth compared to those who had a first stage cesarean (OR = 5.8, p = 0.04). Compared to those delivering vaginally, women whose first delivery ended in a first stage cesarean were less likely to experience preterm birth (OR = 0.30, p = 0.049).
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