Having a cesarean delivery at full dilatation has been associated with increased subsequent risk of spontaneous preterm birth. The Aberdeen Maternity and Neonatal Databank provides a rare opportunity to study subsequent pregnancy outcomes after a previous cesarean delivery at full dilatation over 40 years, with an ability to include a detailed evaluation of potential confounding factors.This study aimed to investigate if having an initial cesarean delivery at full dilatation is associated with spontaneous preterm birth or other adverse pregnancy outcomes in the subsequent pregnancy.A retrospective cohort study was conducted including women with a first and second pregnancy recorded within the Aberdeen Maternity and Neonatal Databank between 1976 and 2017, where previous cesarean delivery at full dilatation at term in the first birth was the exposure. The primary outcome was spontaneous preterm birth (defined as spontaneous birth <37 weeks). Multivariate logistic regression was used to investigate any association between cesarean delivery at full dilatation and the odds of spontaneous preterm birth. Cesarean delivery at full dilatation in previous pregnancy was compared with: (1) any other mode of birth, and (2) individual modes of birth, including planned cesarean delivery, cesarean delivery in first stage of labor (<10-cm dilatation), and vaginal birth (including spontaneous vaginal birth, nonrotational forceps, Kielland forceps, vacuum-assisted birth, breech vaginal birth). Other outcomes such as antepartum hemorrhage and mode of second birth were also compared.Of the 30,253 women included, 900 had a previous cesarean delivery at full dilatation in the first pregnancy. Women with previous cesarean delivery at full dilatation had a 3-fold increased risk of spontaneous preterm birth in a second pregnancy (unadjusted odds ratio, 2.63; 95% confidence interval, 1.82-3.81; adjusted odds ratio, 3.31; 95% confidence interval, 2.17-5.05) compared with those with all other modes of first birth, adjusted for maternal age, diabetes mellitus, body mass index, smoking, preeclampsia, antepartum hemorrhage, socioeconomic deprivation (Scottish Index of Multiple Deprivation 2016), year of birth, and interpregnancy interval (in second pregnancy). When compared with women with vaginal births only, women with cesarean delivery at full dilatation had 5-fold increased odds of spontaneous preterm birth (adjusted odds ratio, 5.37; 95% confidence interval, 3.40-8.48). Compared with first spontaneous vaginal birth, first instrumental births (nonrotational forceps, Kielland forceps, and vacuum births) were not associated with increased risk of spontaneous preterm birth in the second birth. After an initial cesarean delivery at full dilatation, 3.7% of women had a repeated cesarean delivery at full dilatation and 48% had a planned cesarean delivery in the second birth.This study is a substantial addition to the body of evidence on the risk of subsequent spontaneous preterm birth after cesarean delivery at full dilatation, and demonstrates a strong association between cesarean delivery at full dilatation in the first birth and spontaneous preterm birth in subsequent pregnancy, although the absolute risk remains small. This is a large retrospective cohort and includes a comprehensive assessment of potential confounding factors, including preeclampsia, antepartum hemorrhage, and lengths of first and second stage of labor. Future research should focus on understanding possible causality and developing primary and secondary preventative measures. 

Risk of spontaneous preterm birth elevated after first caesarean section at full dilatation: a retrospective cohort study of over 30,000 women.

<h3>Objective</h3> This study aimed to quantify the association between mode of operative delivery in the second stage of labor (cesarean delivery vs operative vaginal delivery) and spontaneous preterm birth in a subsequent pregnancy. <h3>Data Sources</h3> MEDLINE, Embase, EmCare, CINAHL, the Cochrane Library, Web of Science: Core Collection, and Scopus were searched from database inception to April 1, 2023. <h3>Study Eligibility Criteria</h3> All retrospective cohort studies with participants who had a second-stage cesarean delivery (defined as intrapartum cesarean delivery at full cervical dilation) or operative vaginal delivery (including forceps- and/or vacuum-assisted delivery) and that reported the rate of preterm birth (either spontaneous or not specified) in subsequent pregnancy were included. <h3>Methods</h3> Both a descriptive analysis and a meta-analysis were performed. A meta-analysis was performed for dichotomous data using the Mantel-Haenszel random-effects model and used the odds ratio as an effect measure with 95% confidence intervals. The risk of bias was assessed using Cochrane's 2022 Risk Of Bias In Non-randomized Studies of Exposure tool. <h3>Results</h3> After screening 2671 articles from 7 databases, a total of 18 retrospective cohort studies encompassing 605,138 patients were included. The pooled rates of spontaneous preterm birth in a subsequent pregnancy were 6.9% (12 studies) after second-stage cesarean delivery and 2.6% (8 studies) after operative vaginal delivery. A total of 7 studies encompassing 75,460 patients compared the primary outcome of spontaneous preterm birth after second-stage cesarean delivery vs operative vaginal delivery in an index pregnancy with an odds ratio of 2.01 (95% confidence interval, 1.57–2.58) in favor of operative vaginal delivery. However, most studies did not include important confounding factors, did not address exposure misclassification because of failed operative vaginal delivery, and considered operative vaginal delivery as a homogeneous category with no distinction between forceps- and vacuum-assisted deliveries. <h3>Conclusion</h3> Although a synthesis of the existing literature suggests that the risk of spontaneous preterm birth is higher in those with a previous second-stage cesarean delivery than in those with operative vaginal delivery, the risk of bias in these studies is very high. Findings should be interpreted with caution. 

Operative delivery in the second stage of labour and preterm birth in a subsequent pregnancy: a systematic review and meta-analysis.

1. Bjellmo S, Andersen GL, Hjelle S, et al. Does caesarean delivery in the first pregnancy increase the risk for adverse outcome in the second? A registry-based cohort study on first and second singleton births in Norway. BMJ Open. 2020;10(8):e037717. doi:10.1136/bmjopen-2020-037717 CrossRef Google Scholar 

Mode of delivery in the first pregnancy and the potential risk for preterm birth in subsequent pregnancy

Background Previous term (≥37 weeks’ gestation) full dilatation cesarean delivery (FDCD) is associated with an increased risk of subsequent spontaneous preterm birth (sPTB). The mechanism is unknown. We hypothesized that cesarean delivery (CD) scar characteristics and scar position relative to the internal cervical os may compromise cervical function leading to shortening cervical length (CL) and sPTB. Objective To determine the relationship between CD scar characteristics and position assessed by transvaginal ultrasound in pregnant women with previous FDCD and the risk of shortening CL and sPTB. Study design This was a single-center prospective cohort study of singleton pregnant women (14 to 24 weeks’ gestation) with previous term FDCD attending a high-risk preterm birth surveillance clinic (2017–2021). Women underwent transvaginal ultrasound assessment of CL, CD scar distance relative to the internal cervical os and scar niche parameters using a reproducible transvaginal ultrasound technique. sPTB prophylactic interventions (vaginal cervical cerclage or vaginal progesterone) were offered for short CL (≤25mm) or in women with a previous history of sPTB/late miscarriage after FDCD. Primary outcome was sPTB; secondary outcomes included short CL and need for prophylactic interventions. Multivariable logistic regression analysis was used to develop multiparameter models combining CD scar parameters, CL, previous FDCD history and maternal characteristics. Model predictive performance was examined using area under the receiver-operating-characteristics curve (AUC) and detection rate (DR) at various fixed false-positive rates (FPR). The optimal cut-off for CD scar distance to best predict short CL and sPTB was analyzed. Results CD scar was visualized in 90.5% (220/243) of women. sPTB rate was 4.1% (10/243) and 12.8% (31/243) of women developed a short CL. History (n=4) or ultrasound (n=19) indicated cervical cerclage was performed in 23/243 (9.5%) women; 2/23 (8.7%) delivered spontaneously preterm. Multiparameter model based on absolute scar distance from the internal os best predicted sPTB (AUC 0.73, 95%CI, 0.57-0.89, DR of 60% for a fixed 25% FPR). Models based on the relative ‘anatomical’ position of the CD scar to the internal os and CD scar position with niche parameters (length, depth and width) best predicted development of short CL (AUC 0.79, 95%CI 0.71-0.87 and 0.81, 95%CI 0.73-0.89 respectively; DR of 73% at a fixed 25% FPR). sPTB was significantly more likely when the CD scar was <5.0mm above or below the internal os, aOR 6.87 (95%CI 1.34-58; p=0.035). Conclusion In pregnancies following FDCD, CD scar characteristics and distance from the internal os predict women at risk of sPTB and developing short CL. Overall, the sPTB rate was low, but it was significantly increased in women with a scar located <5.0mm above or below the internal cervical os. Shortening of CL was strongly associated with a low scar position. Our novel findings indicate that a low CD scar can compromise the functional integrity of the internal cervical os leading to cervical shortening and/or sPTB. Assessment of CD scar characteristics and position appear to have utility for preterm birth clinical surveillance in women with previous FDCD and could better select women who would benefit from prophylactic interventions. 

Prediction of Spontaneous Preterm Birth in Women with Previous Full Dilatation Cesarean Delivery.

Identification and Management of Presumed Intrapartum Fetal Distress

ObjectivesAn increased risk of preterm birth (PTB) following a caesarean section (CS) in the second stage of labor has been demonstrated. We aimed to investigate the relationship between the station of the presenting fetal part and the surgical technique at first CS, and the risk of subsequent PTB.Study designThis was a cohort study of 11,850 women in Sweden, delivered by CS in 2001–2007 at any of 23 birth units, with a second delivery in 2001–2009. Clinical information was retrieved from electronic birth records linked to national health registers. The risk of subsequent PTB was analyzed by fetal station, defined as low (at or below the ischial spines) or high (above the ischial spines), and aspects of the surgical technique at index CS. Associations were explored with logistic regression and results are presented as odds ratios (ORs) with 95% confidence intervals (CIs), by type and severity (very early < 32 gestational weeks and moderate preterm 32–36 gestational weeks) of PTB. Multiple logistic regression included adjustments for maternal age, gestational age at first delivery, and inter-delivery interval.ResultsOut of 11,850 women delivered by CS, 1,016 (8.6%) delivered preterm in their subsequent pregnancy. There was an increased likelihood of spontaneous PTB, but not with medically indicated PTB, after an index CS with the fetal presenting part at a low station (aOR 1.61, 95% CI 1.23–2.11). CS performed at a low station was associated with birth < 32 gestational weeks (aOR 1.73, 95% CI 1.05–2.84) and birth at 32–36 gestational weeks (aOR 1.29, 95% CI 1.00–1.65), compared with high fetal station. Thickness of the uterine wall, incision type, and closure of the uterus at index CS did not affect the risk.ConclusionA primary CS at a low station was associated with a subsequent spontaneous PTB, but not medically indicated PTB. Surgical technique at index CS did not alter the risk. 

Fetal station at Caesarean section and risk of subsequent preterm birth - a cohort study

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Fetal station at Caesarean section and risk of subsequent preterm birth - a cohort study