# Risk of recurrent spontaneous preterm birth following preterm full dilatation cesarean delivery

## TL;DR

Women who had a preterm full dilatation cesarean delivery face a higher risk of another early birth compared to other preterm delivery methods.

## Contribution

This study reveals that preterm full dilatation cesarean delivery increases the risk of recurrent spontaneous preterm birth more than other preterm delivery modes.

## Key findings

- Recurrent sPTB <37 weeks was 38.1% in preterm FDCD cases, significantly higher than vaginal or early CD cases.
- Recurrent sPTB <34 weeks was 23.8% in preterm FDCD cases, much higher than in other groups.
- Most CD scars in preterm FDCD cases were located within the cervix or near the internal cervical os.

## Abstract

Term full dilatation cesarean delivery (FDCD) is associated with an increased risk of subsequent spontaneous preterm birth (sPTB). The impact of preterm FDCD on recurrent sPTB is unknown. We investigated the relationship between recurrent sPTB and the mode of prior sPTB.

This is a retrospective cohort study of singleton pregnant women attending two high‐risk preterm birth surveillance clinics (University College London Hospital and St Thomas' Hospital London, UK), with one previous sPTB (24–36 + 6 weeks). Women were categorized according to their mode of birth in the index sPTB pregnancy: (1) preterm FDCD, (2) preterm vaginal birth and (3) preterm cesarean delivery at <10 cm cervical dilatation (CD < 10 cm). The primary outcome was recurrent sPTB <37 weeks of gestation. Secondary outcomes included sPTB <34 weeks, <28 weeks, spontaneous late miscarriage and short cervical length (≤25 mm). In a subgroup of women with preterm FDCD, CD scar characteristics were assessed during the second trimester of pregnancy using transvaginal ultrasound.

Median gestation of prior sPTB was similar across all groups (32 weeks; p = 0.454). Recurrent sPTB <37 weeks was significantly more common in women with previous preterm FDCD, 38.1% (8/21) compared to vaginal birth, 15.1% (16/106) or CD < 10 cm, 13.8% (15/109); aOR 4.4 (95% CI 1.3–14.9; p = 0.023) and 5.1 (95% CI 1.6–16.5; p = 0.022), respectively. Recurrent sPTB <34 weeks was even higher in the previous preterm FDCD group, 23.8% (5/21) compared to vaginal birth 4.7% (5/106) or CD < 10 cm 8.3% (9/109); aOR 16.6 (95% CI 2.8–97.2; p = 0.016) and 5.7 (95% CI 1.4–23.1; p = 0.022), respectively. CD scar location was assessed in 15 women with preterm FDCD in one centre. Scar visualization was 87%, with 77% (10/13) of scars being located within the cervix or <5 mm above the internal cervical os.

Women undergoing FDCD following preterm labor have a significantly higher risk of recurrent sPTB at <37 and <34 weeks of gestation compared to women with previous preterm vaginal birth or CD prior to the second stage of labor. These findings suggest that preterm FDCD may further compromise cervical function. It is important that clinicians are aware of this increased risk of recurrent sPTB to guide patient counseling and management accordingly.

Women with a history of spontaneous preterm labor resulting in full dilatation cesarean delivery have a higher risk of recurrent spontaneous preterm birth than those with prior preterm vaginal birth or first stage cesarean delivery. Clinicians should be aware of these risks to guide counseling and management in subsequent pregnancies.