Risk of Spontaneous Preterm Birth in a Subsequent Pregnancy After Full Dilatation Caesarean Birth: A Nationwide Cohort Study.

OBJECTIVE

To investigate the association between caesarean birth in the second stage of labour and the risk of spontaneous preterm birth in a subsequent pregnancy.

DESIGN

Nationwide register-based cohort study.

SETTING

The Danish Medical Birth Registry and The Danish National Patient Register from 1997 to 2021.

POPULATION

Women with at least two consecutive births (index birth and subsequent birth) where the index birth was a term singleton.

METHODS

Women with spontaneous preterm subsequent birth were compared according to the mode of index birth, including vaginal, prelabour caesarean, first stage caesarean and second-stage caesarean. Statistical analysis was performed using multiple logistic regression.

MAIN OUTCOME MEASURE

Spontaneous birth before 37 + 0 gestational weeks.

RESULTS

A total of 376 414 women met the inclusion criteria. Distribution of mode of index birth was vaginal 318 117 (84.5%), prelabour caesarean 15 373 (4.1%), first stage caesarean 37 547 (10.0%) and second-stage caesarean 5377 (1.4%), respectively. The rate of subsequent preterm birth was 1.7%. Compared to vaginal birth, a second-stage caesarean was associated with an increased risk of preterm birth in a subsequent pregnancy (adjusted odds ratio [aOR] 1.46, 95% confidence interval [CI] 1.21-1.77). Similarly, compared to first stage caesarean, a second-stage caesarean was associated with an increased risk of preterm birth in the subsequent pregnancy, with an aOR of 1.41 (95% CI 1.15-1.74).

CONCLUSION

Second-stage caesarean in a previous term pregnancy is associated with an increased risk of spontaneous preterm birth in a subsequent pregnancy.