Study population

This was a retrospective, population-based cohort study of all women with at least 2 previous CDs who delivered at term between 37 0/7 and 40 6/7 weeks of gestation in Ontario, Canada, between April 2012 and March 2019. All permanent residents of Ontario receive universal health coverage under the government-funded provincial health insurance plan. Women with a multifetal pregnancy or a major fetal anomaly were excluded. Data were obtained from the Better Outcomes Registry & Network (BORN) Ontario ( https://www.bornontario.ca/en/about-born/ ), which is a province-wide registry of all births recorded in Ontario, Canada. On admission to the labor and delivery unit, data were collected for each parturient by healthcare providers and hospital staff from charts, clinical forms, and patient interviews and then entered into the BORN Information System (BIS). The BIS contains information on maternal demographics, health behaviors, and reproductive history, and clinical information pertaining to pregnancy, labor, birth, and fetal and neonatal outcomes. An ongoing program of data verification, quality assurance, and formal training sessions for individuals collecting and entering data guarantees that a high level of data quality is maintained.

For all study years, the BORN data were linked with maternal and newborn discharge abstracts from the Canadian Institute for Health Information’s Discharge Abstract Database (DAD). This database contains a set of validated diagnostic codes from the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Canadian version (ICD-10-CA) and intervention codes from the Canadian Classification of Health Interventions for all in-hospital deliveries. This linkage of the BORN and DAD databases ensures the highest probability of identifying maternal and neonatal diagnoses from all special-care nursery units in Ontario.

This study was approved by our local institutional review board (IRB#131-2018).

Definitions and comparison groups

The timing of delivery was determined in terms of completed gestational weeks so that 39 weeks, for example, included deliveries from 39 0/7 to 39 6/7 weeks of gestation. Gestational age was based on the best obstetrical estimate (last menstrual period compared with ultrasound measurements) determined by the treating healthcare provider. In Ontario, 75.3% of women have a first trimester ultrasound. For the purpose of this analysis, we regarded any elective CD performed solely for the indication of 2 previous CDs as an elective CD. This category included CDs performed on maternal request and those performed for a declined trial of labor after CD (TOLAC). We present all term deliveries until 40 6/7 weeks’ gestation to reflect the current practice of timing of delivery in Ontario. However, because elective delivery at 40 weeks’ gestation and beyond is uncommon among women with at least 2 previous CDs, we only analyzed women undergoing elective CD between 37 0/7 and 39 6/7 weeks of gestation.

In an attempt to mimic the clinical decision making process, we compared elective CD at each gestational week, from 37 0/6 to 39 6/7 weeks, with cases that were managed expectantly during that week and those that were delivered from the beginning of the following week and onward so that women electively sectioned at 37 0/7 to 37 6/7 weeks were compared with women who delivered from 38 0/7 weeks onward. This comparison group included women who delivered either by an elective CD at a later date, an obstetrically indicated repeat CD, a CD performed after labor onset, or vaginal delivery ( Figure ). Obstetrically indicated repeat CDs were defined as any CD performed for indications other than a previous CD (eg, hypertensive disorders of pregnancy or placental abruption).

Flow chart description of the study and control groups (2012–2019)

The dashed lines represent groups not included in the statistical analysis. An elective CD was defined as any women who had an indication for CD either because of maternal request, a previous CD, or a declined trial of labor after CD.

CD , cesarean delivery; VD , vaginal delivery.

Shinar et al. Timing of cesarean delivery in women with ≥ 2 previous cesarean deliveries. Am J Obstet Gynecol 2022.

Outcomes

The primary outcome was a composite of maternal outcomes, including mortality and severe maternal morbidity as previously defined. This was identified through the ICD-10-CA diagnosis codes and the Canadian Classification of Health Interventions procedure codes associated with severe maternal illness. Specifically, these outcomes comprised uterine rupture or dehiscence, placental abruption, intra- or postoperative surgical complications (including CD or postpartum hysterectomy, repair of bladder, urethra, or intestines, and embolization or ligation of pelvic vessels or B-Lynch suture of uterus), postpartum blood transfusions, ICU admissions, other postpartum complications (including puerperal sepsis, deep vein thrombosis, or pulmonary embolism and evacuation of incisional hematoma), and prolonged hospital stay of >1 week. The composite maternal outcome (any 1 of the above or a combination of the above) was calculated. Additional outcomes, relevant only to the expectant management group, included hypertensive disorders of pregnancy (including gestational hypertension and preeclampsia) and placental abruption.

Secondary outcomes were neonatal outcomes. These included stillbirth, neonatal death, neonatal respiratory morbidity, 5-minute Apgar score of <7, arterial blood cord pH of <7.1, neonatal ICU (NICU) admission of >24 hours, seizures or hypoxic-ischemic encephalopathy, and sepsis. Neonatal respiratory morbidity was defined as any of the following: transient tachypnea of the newborn, need for respiratory support in the form of continuous positive airway pressure, mechanical ventilation, or respiratory distress syndrome. The composite neonatal outcome (any one of the above or their combination) was calculated.

Statistical analysis

The baseline characteristics and maternal and neonatal outcomes were compared between the elective CD group at each gestational week and the expectant management group. Chi-square test or Fisher exact test was used for categorical variables and Wilcoxon rank sum test or 2-sample t test was used for continuous variables. Significance was set at a 2-sided P value of <.05.

Crude and adjusted risk ratios for the study outcomes in the elective CD vs expectant management groups were calculated at each gestational week using clustered logistic regression analyses. The analysis was adjusted for pregestational body mass index (BMI), maternal age, number of previous CDs, previous vaginal deliveries, and gestational weight gain. We chose these variables because of their potential association with maternal outcomes. For example, a high pregestational BMI, increased gestational weight gain, and more previous CDs may lead to longer, more complex surgeries with a greater risk for blood loss and intra- and postoperative complications. Previous vaginal deliveries impact TOLAC potential and thus maternal outcomes. Multiple imputation was used to improve the rate of missing data for the pregestational BMI variable. Additional potential confounders, including ethnicity, smoking, preexisting maternal comorbidities (gestational and pregestational diabetes and chronic hypertension), and maternal and fetal levels of care, were evaluated using a change in estimate approach. Variables that did not meet the 10% cutoff used to identify confounders were not included in the final regression models.

Descriptive statistics were used to describe the rate of complications relevant only to the expectant management groups (hypertensive disorders of pregnancy and placental abruption). The anticipated fraction of urgent CD (defined as CD performed for an obstetrical indication or CD performed while in labor) for each gestational week was calculated pragmatically as the number of women who underwent an urgent CD during or before that gestational week divided by the number of women who remained pregnant after that completed gestational week multiplied by 100.

Data were analyzed using SAS statistical software, version 9.4 (SAS Institute Inc, Cary, NC).

Characteristics of the study population

A total of 985,530 women had a hospital birth in Ontario, Canada, during the study period of whom 30,464 (3.09%) had at least 2 previous CDs. A total of 26,522 women met the inclusion criteria and delivered between 37 0/7 and 40 6/7 weeks of gestation ( Figure ). This cohort was divided into 3 comparison groups, 1 for each gestational week, and among those, women who underwent elective CD were compared with those who underwent expectant management. As such, 1345 women who underwent an elective CD during the 37th week of gestation were compared with 23,417 women who were managed expectantly during the corresponding weeks and who delivered from 38 0/7 weeks of gestation onward. The latter was made up of women who underwent a CD, either elective or during labor and either indicated or nonindicated, and women who delivered vaginally. Similarly, 7708 women who underwent an elective CD during the 38th week of gestation were compared with 12,225 women who were managed expectantly during the corresponding weeks and who delivered from 39 0/7 weeks of gestation onward.

Overall, the characteristics of women in the elective CD and expectant management groups were similar with regards to maternal age and gestational weight gain. At any given week between 37 0/7 and 38 6/7 weeks, women in the elective CD group were more likely to be Black, to have pregestational and gestational diabetes, and to have had >2 previous CDs than women in the expectant management group. The rates of chronic hypertension did not differ between the elective and expectant management groups across all gestational ages that were compared. Women with a previous vaginal delivery who remained undelivered at 39 0/7 weeks’ gestation were more likely to be managed expectantly and deliver after 39 6/7 weeks’ gestation ( P <.0001) ( Table 1 ).

Maternal outcomes

The incidence of the composite maternal outcome was comparable between elective delivery at 37 0/7 to 37 6/7 weeks’ gestation and expectant management and between elective delivery at 38 0/7 to 38 6/7 weeks’ gestation and expectant management. Conversely, elective delivery at 39 0/7 to 39 6/7 weeks’ gestation was associated with a significantly lower risk for the composite adverse outcome than expectant management from 40 0/7 weeks’ gestation (2.1% vs 3.2%; P =.02) ( Table 2 ). Maternal death, placental abruption, intra- and postoperative surgical complications, other postpartum complications, postpartum blood transfusions, and ICU admissions were rare events across all gestational age groups and the incidence thereof did not differ significantly between the elective CD and expectant management groups.

Neonatal outcomes

The composite adverse neonatal outcome was greater for elective CD at 37 and 38 weeks’ gestation than for expectant management (23.3% vs 12.7% at 37 weeks; P <.0001 and 12.8% vs 11.4% at 38 weeks; P =.004) ( Table 3 ). This was mostly driven by the higher rates of respiratory morbidity and NICU stay >24 hours in the elective CD group ( P <.001 for both outcomes) and a higher risk for sepsis ( P =.02) and incidence of 5-minute Apgar score <7 ( P =.0001) in the elective delivery at 37 weeks group. Conversely, beyond 39 weeks of gestation, expectant management was associated with an increased risk for the composite adverse neonatal outcome (13.6% vs 10.4%; P =.001). This was driven mainly by higher rates of respiratory morbidity (9.3% vs 7.0%; P <.001), 5-minute Apgar score <7 (1.3% vs 0.5%; P =.002), and NICU stay >24 hours (6.8% vs 4.0%; P <.0001). Stillbirth, neonatal death, seizures, and hypoxic-ischemic encephalopathy were rare events that did not differ significantly in incidence across gestational ages.

Table 3

Neonatal outcomes of elective delivery at a specific gestational week compared with expectant management beyond that week

Neonatal outcomes	Elective CD (37+0 to 37+6 wk) n=1345 n (%)	Expectant (38+0 wk) a n=23,417 n (%)	P value	Elective CD (38+0 to 38+6 wk) n=7708 n (%)	Expectant (39+0 wk) a n=12,225 n (%)	P value	Elective CD (39+0 to 39+6 wk) n=8929 n (%)	Expectant (40+0 wk) a n=1111 n (%)	P value
Composite neonatal outcome b	314 (23.3)	2977 (12.7)	<.0001 c	984 (12.8)	1396 (11.4)	.004 c	926 (10.4)	151 (13.6)	.001 c
Stillbirth	<6 (S)	22 (0.1)	1.0	<6 (S)	<6 (S)	N/A	0	<6 (S)	.11
Neonatal death	<6 (S)	13 (0.1)	.54	<6 (S)	<6 (S)	N/A	<6 (S)	<6 (S)	N/A
Respiratory morbidity d	238 (17.7)	2009 (8.9)	<.0001 c	692 (9.0)	925 (7.6)	<.001 c	621 (7.0)	103 (9.3)	<.001 c
5-min Apgar score <7	30 (2.2)	202 (0.9)	<.0001 c	62 (0.8)	88 (0.7)	.50	45 (0.5)	14 (1.3)	.002 c
Arterial cord pH <7.1	30 (2.2)	514 (2.2)	.93	138 (1.8)	274 (2.2)	.03 c	187 (2.1)	25 (2.3)	.73
NICU length of stay >24 h	175 (13.0)	1375 (5.9)	<.0001 c	493 (6.4)	576 (4.7)	<.0001 c	355 (4.0)	76 (6.8)	<.0001 c
Sepsis	16 (1.2)	156 (0.7)	.02 c	41 (0.5)	60 (0.5)	.69	41 (0.5)	6 (0.5)	.71
Seizures or hypoxic-ischemic encephalopathy	<6 (S)	30 (0.1)	.69	10 (0.1)	13 (0.1)	.64	7 (0.1)	<6 (S)	.26

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