Mode of delivery and preterm birth in subsequent births: A systematic review and meta-analysis

Abstract

Preterm birth continues to be an important problem in modern obstetrics and a large public health concern and is related to increased risk for neonatal morbidity and mortality. The aim of this study was to evaluate the data in the literature to determine the relationships between mode of delivery (cesarean section and vaginal birth) in the first pregnancy and the risk of subsequent preterm birth from a multi-year population based cohorts (PROSPERO registration number: 42018090788). Five electronic databases were searched. Observational studies that provided mode of delivery and subsequent preterm birth were eligible. Ten cohort studies, involving 10333501 women, were included in this study. Compared with vaginal delivery, women delivering by previous cesarean section had a significantly higher risk of preterm birth in subsequent births (RR 1.10, 95%CI 1.01–1.20). After adjusting confounding factors, there was still statistical significance (aRR 1.12, 95%CI 1.01–1.24). However, both before and after adjustment, there was no difference among very preterm birth (RR 1.14, 95%CI 0.90–1.43; aRR 1.16, 95%CI 0.80–1.68; respectively). To the best of our knowledge, this is the first systematic review and meta-analysis that suggests previous cesarean section could increase the risk of preterm birth in subsequent pregnancies. The result could provide policy makers, clinicians, and expectant parents to reduce the occurrence of unnecessary cesarean section.

Risk of preterm birth after prior term cesarean

“…Previous publications on the association between a CS in the first and PTB in the second pregnancy also show an increased risk of PTB after a term CS . Nevertheless, the effect size is not concordant between studies.…”

“…However, there was no distinction made between spontaneous and iatrogenic PTB in this cohort, which might be an explanation for the greater effect size of this study . A recently published systematic review shows results similar to ours, concluding that prior CS (both for elective and emergency indications) shows an increased risk of subsequent PTB >32 weeks of pregnancy . Another very recent publication of an American cohort study with a comparable design to our study shows higher incidence of spontaneous PTB and iatrogenic PTB after CS at term; however, none of those results was statistically significant after adjustment for confounding factors such as the indication for the prior CS …”

“…5 A recently published systematic review shows results similar to ours, concluding that prior CS (both for elective and emergency indications) shows an increased risk of subsequent PTB >32 weeks of pregnancy. 30 Another very recent publication of an American cohort study with a comparable design to our study shows higher incidence of spontaneous PTB and iatrogenic PTB after CS at term; however, none of those results was statistically significant after adjustment for confounding factors such as the indication for the prior CS. 29 However, despite these observations, the pathophysiological pathway towards preterm birth after prior CS remains Possible pathways include abnormal placental implantation, changed uterine microenvironment with or without increased inflammation, disruption or dehiscence of tissue, affected cervical function due to cervical damage during the prior CS or stasis of fluid or blood in the lower uterine segment that might induce the cascade leading to preterm birth.…”

“…Previous publications on the association between a CS in the first and PTB in the second pregnancy also show an increased risk of PTB after a term CS. 4,5,[29][30][31] Nevertheless, the effect size is not concordant between studies. In a large nationwide individual patient-level analysis, an odds ratio of 1.2 (95% CI 1.1-1.4) for overall PTB in the second pregnancy and odds ratios of 1.4-1.9 for spontaneous PTB were reported, 4 which is in line with our results.…”

“…29 However, despite these observations, the pathophysiological pathway towards preterm birth after prior CS remains Possible pathways include abnormal placental implantation, changed uterine microenvironment with or without increased inflammation, disruption or dehiscence of tissue, affected cervical function due to cervical damage during the prior CS or stasis of fluid or blood in the lower uterine segment that might induce the cascade leading to preterm birth. 13,[30][31][32] For instance, in women with prior CS the incidence of a scar dehiscence (in the absence of uterine scar rupture) has been reported to be 3.2% and is associated with preterm birth in a subsequent pregnancy. 33…”