Study population

This was a retrospective cohort study of all women with GDM who had a singleton hospital birth at ≥38 + 0 weeks of gestation in Ontario, Canada, between April 2012 and March 2014. Data were obtained from the Better Outcomes Registry & Network (BORN) Ontario ( https://www.bornontario.ca/en/about-born/ ) BORN Ontario is a province-wide registry of all births in Ontario, Canada. Whenever a woman is admitted to a hospital to give birth, data are collected by health care providers and hospital staff from charts, clinical forms, and patient interview then entered into the BORN Information System (either directly or by electronic upload from a hospital’s electronic medical records system). The BORN Information System contains maternal demographics, health behaviors, reproductive history, and clinical information related to pregnancy, labor, and birth, fetal, and neonatal outcomes. An ongoing program of data verifications, quality checks, and formal training sessions for individuals who collect and enter data assures that a high level of data quality is maintained.

To create a “low-risk” GDM cohort, women with any of the following conditions were excluded from the study: gestational age at birth of ≥42 + 0 weeks, women who were not candidates for vaginal birth (eg, nonvertex presentation, placenta previa), previous cesarean delivery, major fetal anomalies, or chronic maternal medical conditions that potentially could influence a decision to induce labor at 38-39 weeks of gestation that include pre-GDM, chronic hypertension, chronic renal disease, cardiac disease (congenital or acquired), pulmonary disease (pulmonary hypertension, cystic fibrosis, pulmonary embolism), autoimmune conditions (systemic lupus erythematosus), or hematologic diseases (hemophilia, sickle cell disease; Figure ).

Description of the study and control groups

Selection of the induction and expectant management groups at 38 and 39 weeks. The asterisk refers to chronic medical conditions that include pregestational diabetes mellitus, chronic hypertension, and renal, cardiac, pulmonary, vascular, and hematologic diseases that could influence a primary decision to induce labor at 38-39 weeks of gestation.

CS , cesarean delivery; GDM , gestational diabetes mellitus.

Melamed et al. Induction of labor in GDM. Am J Obstet Gynecol 2016 .

Some of the previous observational studies on the effects of IOL are limited by the use of a control group of women who experience spontaneous onset of labor. However, in clinical practice, the real choice is not between IOL and spontaneous labor, but between IOL and expectant management; the latter option carries that risk of new onset of pregnancy complications and the potential for labor induction at a later stage of gestation. Thus, to simulate the decision faced by physicians in real-life, women who underwent IOL at 38 + 0 to 38 + 6 weeks of gestation in the current study (38-IOL group) were compared with those who were treated expectantly and remained undelivered until 39 + 0 weeks of gestation (ie, delivered anytime between 39 + 0 and 41 + 6 weeks of gestation; 38-Expectant group). A separate comparison was performed between women who underwent IOL at 39 + 0 to 39 + 6 weeks of gestation (39-IOL group) and those who were treated expectantly and remained undelivered until 40 + 0 weeks (ie, delivered anytime between 40 + 0 and 41 + 6 weeks of gestation; 39-Expectant group; Figure ). Only women whose sole documented reason for IOL was GDM or macrosomia were included in the 38-IOL and 39-IOL groups ( Figure ).

Outcomes

The primary outcome was the rate of cesarean delivery. Secondary outcomes included the rate of instrumental delivery, postpartum hemorrhage, intrapartum fever, anal sphincter injury (defined as a third- or fourth-degree perineal laceration), shoulder dystocia, and neonatal morbidity. Neonatal respiratory morbidity was defined as any of the following events: need for respiratory support in the form of continuous positive airway pressure or mechanical ventilation, a diagnosis of transient tachypnea of the newborn infant, or respiratory distress syndrome. Composite neonatal morbidity was defined as the presence of any of the following events: perinatal death, 5-minute Apgar score <7, admission to the neonatal intensive care unit (NICU), hypoglycemia, jaundice that required phototherapy, or neonatal respiratory morbidity.

Diagnosis of GDM

This study spans 2 time periods with regards to criteria for the diagnosis of GDM in Ontario. Before April 2013, the criteria for diagnosis were according to 2008 Canadian Diabetes Associations guidelines. These guidelines recommended screening for GDM with a 50 g glucose challenge test (GCT); when the results were positive (>7.8 mmol/L or 140 mg/dL), a 75g oral glucose tolerance test (OGTT) followed (cutoff values: fasting, ≥5.3 mmol/L or 96 mg/dL; 1 hour ≥10.6 mmol or 191 mg/dL; 2 hours ≥ 8.9 mmol/L or 160 mg/dL). GDM was defined as ≥2 abnormal OGTT values or a GCT result of ≥10.3 mmol/L or 185 mg/dL. The presence of a single abnormal OGTT value was defined as impaired glucose tolerance.

In April 2013 new Canadian Diabetes Associations criteria were published. The new guidelines allowed two options for screening/testing for GDM. The “Preferred” option was essentially identical to the Canadian Diabetes Associations 2008 guidelines aside from increasing the diagnostic 50g-GCT value from 10.3 mmol (185 mg/dL) to ≥ 11.1 mmol (200 mg/dL), and the 2-hour 75g-OGTT threshold from 8.9 mmol/L (160 mg/dL) to 9.0 mmol/L (162 mg/dL). The distinction between impaired glucose tolerance and GDM was eliminated in these new guidelines.

Data analysis

Multivariable logistic regression analysis was used to adjust for potential confounding variables that included maternal age (as a continuous variable), nulliparity, need for insulin treatment, prepregnancy BMI (as a continuous variable), and macrosomia (birthweight, >4000 g). This analysis was repeated within a subgroup of nulliparous women, because parity is a major determinant of the success of labor induction. In addition, because we did not have data about the Bishop’s cervix score (which is associated with the likelihood of successful induction), we assumed that variation in this score would likely be low among nulliparous women.

Data were analyzed using the SAS statistical software (version 9.4; SAS Institute Inc, Cary, NC). Significance was set at a 2-sided probability value of <.05. The current study was approved by the Sunnybrook Health Sciences Center Research Ethics Board.

Characteristics of the study population

During the study period, 281,480 women gave birth in hospitals in Ontario, Canada, 14,600 (5.2%) of whom were diagnosed with GDM, of whom 8392 were eligible for the study ( Figure ). Overall 1188 women who underwent IOL at 38 + 0 to 38 + 6 weeks of gestation for GDM-related reasons (38-IOL group) were compared with 5229 women who remained undelivered until at least 39 + 0 weeks (38-Expectant group). Similarly, 1036 women who underwent IOL at 39 + 0 to 39 + 6 weeks of gestation for GDM-related reasons (39-IOL group) were compared with 2162 women who remained undelivered until at least 40 + 0 weeks of gestation (39-Expectant group).

The characteristics of the induction and expectant groups are presented in Table 1 . Women in the induction groups were older, less likely to be nulliparous, more likely to require insulin treatment, and had a higher prepregnancy BMI.

Pregnancy complications

Women in the 38-IOL and 39-IOL groups had a lower rate of cesarean delivery compared with women in the 38-Expectant and 39-Expectant groups, respectively (16.7 % vs 21.3% [ P < .001] and 19.6% vs 22.9% [ P = .04], respectively; Table 2 ). The rates of instrumental deliveries were similar between the induction and expectant groups.

The rate of anal sphincter injuries was lower in women in the 38-IOL group compared with those in the 38-Expectant group (2.3% vs 3.8%; P = .01); similar differences were not observed between women in the 39-IOL and 39-Expectant groups ( Table 2 ).

Women in the 38-Expectant and 39-Expectant groups were at risk of new-onset of hypertensive complications (5.6% and 4.8%, respectively) and eventually underwent labor induction in 47.% and 48.3% of cases, respectively ( Table 2 ).

Neonatal outcomes

Infants of mothers in the 38-IOL and 39-IOL groups were less likely to have a birth weight >4000 g compared with women in the 38-Expectant and 39-Expectant groups, respectively (9.1% vs 12.7% [ P < .001] and 12.4% vs 15.5% [ P = .02], respectively; Table 3 ).

Table 3

Neonatal outcomes in the induction and expectant management groups

Outcome	Weeks of gestation
	38			39
	Induction (n = 1188)	Expectant management (n = 5229)	P value	Induction (n = 1036)	Expectant management (n = 2162)	P value
Gestational age at delivery, wks a	38.4 ± 0.3	39.8 ± 0.7	< .001	39.3 ± 0.3	40.5 ± 0.5	< .001
Birthweight, g a	3362 ± 468	3486 ± 474	< .001	3473 ± 483	3557 ± 461	< .001
>90th Percentile b	117 (9.9)	521 (10.0)	.9	103 (9.9)	214 (9.9)	.9
>4000 gr	108 (9.1)	666 (12.7)	< .001	128 (12.4)	335 (15.5)	.02
>4500 gr	17 (1.4)	128 (2.5)	.03	23 (2.2)	64 (3.0)	.2
Composite morbidity c	355 (29.9)	1550 (29.6)	.9	282 (27.2)	673 (31.1)	.02
Perinatal mortality	0 (0.0)	8 (0.2)	.4	0 (0.0)	5 (0.2)	.2
Neonatal intensive care unit admission	165 (13.9)	567 (10.8)	.002	103 (9.9)	247 (11.4)	.2
Total length of stay at neonatal intensive care unit, d a	3.0 ± 3.8	3.2 ± 4.8	.6	3.1 ± 5.0	2. 9 ± 3.3	.7
Respiratory morbidity d	36 (3.0)	188 (3.6)	.3	27 (2.6)	89 (4.1)	.03
Jaundice requiring phototherapy	59 (5.0)	178 (3.4)	.01	39 (3.8)	70 (3.2)	.4
Hypoglycemia	74 (6.2)	211 (4.0)	< .001	49 (4.7)	77 (3.6)	.1

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