Likelihood of primary caesarean delivery following induction of labour
in singleton term pregnancies, compared to expectant management: a
population-based, retrospective cohort study
Abstract
Background: There has been a trend toward birth at earlier
gestational age and increased use of both induction of labour (IOL) and
caesarean section (CS) for women with term pregnancies in many
countries, particularly high-income countries. Unnecessary use of
obstetric interventions during pregnancy and birth is associated with an
increased risk of adverse health outcomes for women and babies, as well
as adding financial costs to the health care systems. Existing evidence
regarding the association between IOL at term and CS is mixed and
conflicting, and little evidence has been known about the differential
effect at each gestation between 37 +0 – 41
+6 weeks, separately among nulliparous and parous
women. Objective: The aim of this study was to explore the
association between IOL and primary CS for women with singleton term
pregnancies, compared with expectant management (EM) of pregnancy.
Methods: We performed an analysis of population-based
retrospective cohort data on women who gave birth in one Australian
state (Queensland), between 01/07/2012 and 30/06/2018. All no-labour
births (i.e., prelabour CS), multiple births (e.g., twins or triplets),
and women with a prior CS were excluded. Five sub-datasets were created
based on the time of birth following IOL (37 +0 - 37
+6; 38 +0 - 38 +6;
39 +0 - 39 +6; 40
+0 - 40 +6; and 41
+0 - 41 +6). Unadjusted relative
risk (RR) and adjusted relative risk (aRR) were calculated in each
sub-dataset to explore the risk of primary CS following IOL, compared to
EM. Analysis was stratified by parity (nulliparas versus paras).
Sensitivity analyses were conducted by limiting to women with low-risk
pregnancies. Results: The risk of primary CS following IOL was
significantly higher for women with singleton pregnancies, compared with
EM, before or after adjustment, at 38 +0 - 38
+6 (nulliparas: aRR = 1.14, 95% CI: 1.10 - 1.18;
paras: aRR = 1.35, 95% CI: 1.25 - 1.46), at 39 +0 -
39 +6 (nulliparas: aRR = 1.18, 95% CI: 1.14 - 1.22;
paras: aRR = 1.36, 95% CI: 1.24 - 1.49), at 40 +0 -
40 +6 (nulliparas: aRR = 1.25, 95% CI: 1.21 - 1.29;
paras: aRR = 1.40, 95% CI: 1.26 - 1.56) and at 41 +0
- 41 +6 (nulliparas: aRR=1.42, 95% CI: 1.36 - 1.48;
paras: aRR=1.61, 95% CI: 1.40 - 1.84). After adjusting for potential
confounders, there was no significant difference in the risk of primary
CS at 37 +0 - 37 +6 for nulliparas
who had IOL and EM (aRR = 1.03, 95% CI: 0.95 - 1.12). Results remain
stable in the sensitivity analyses. Conclusion: Our results
demonstrated that the risk of primary CS following IOL was higher at
each weeks’ gestation between 38 +0 - 38
+6 – 41 +0 - 41
+6 for both nulliparas and paras with singleton
pregnancies, compared with EM, and the risk increased with gestational
age. This has important implications to support shared decision making
between women and health professionals regarding best clinical
management and optimal timing of birth.