Results
There were 5,984,942 pregnancies available for review from the NCHS and CDC’s Division of Vital Statistics database from January 1st, 2015 to December 31st, 2017. The data from a total of 1,885,694 singleton, non-anomalous pregnancies that met inclusion criteria were abstracted from the database. Of these pregnancies, 424,690(22.5%) women underwent induction of labor at 39 weeks gestation, while the remaining 1,461,004 (77.5%) women delivered spontaneously after expectant management through 42 weeks and 0/7 days gestation (Figure 1).
Maternal demographics and clinical characteristics were similar between the two groups and are summarized in Table 1. In both groups, the mean maternal age was 28.0 years; the most common race was White followed by Black; the majority of women had a high school diploma or above in terms of education; and the mean body mass index (BMI) was 26.7 in the induction of labor group and 26.0 in the expectant management group. Approximately half of the women in each group had a prior vaginal delivery.
Maternal outcomes were analyzed for both the induction of labor and the expectant management group. The results are summarized in Table 2. Maternal morbidity was evaluated by comparing the frequency of triple I, blood transfusion, ICU admission, uterine rupture, cesarean hysterectomy, and cesarean delivery between the two groups. All results were adjusted for obesity, education, race and prior vaginal delivery. Mothers were significantly less likely to be diagnosed with triple I in the induction of labor group when compared to the expectant management group (p-value < 0.001; aRR: 0.66; 95% CI [0.64-0.68]) and had a decreased rate of cesarean section (p-value <0.01; aRR 0.69l 95% CI [0.68-0.69]) in the expectant management group. The cesarean hysterectomy rate was approximately 2 per 10,000 deliveries for the entire cohort. Women who underwent induction of labor were over 30% more likely to have undergone a cesarean hysterectomy (p-value <0.01; aRR 1.32; 95% CI [1.05-1.65]). Conversely, there were no differences between the two groups in maternal frequency of blood transfusion, ICU admission, or uterine rupture.
Neonatal outcomes were analyzed for both the induction of labor and the expectant management group. A summary of the results can be found in Table 3. Neonatal morbidity was evaluated by comparing the risk of neonates with 5 min Apgar ≤3, prolonged ventilation, NICU admission, seizure, and neonatal death between the two groups. All results were adjusted for obesity, education, race and prior vaginal delivery. Neonates in the induction group were significantly less likely to have: (i) 5 min Apgar ≤3 (p-value < 0.01; aRR 0.69; 95% CI [0.64-0.74]), (ii) require prolonged ventilation (p-value < 0.01; aRR 0.77; 95% CI [0.72-0.82]), (iii) necessitate NICU admission (p-value < 0.01; aRR 0.80; 95% CI [0.79-0.82), and/or (iv) neonatal seizures (p-value <0.01; aRR 0.80; 95% CI [0.66-0.98]) when compared to the expectant management group. Conversely, there was no difference in the frequency of neonatal death between the two groups.