Table 3.
Characteristics of Deliveries by Induction Status
| Characteristica | Not induced n=178,404%c | Indicated inductionb n=50,583%c | Elective inductionb n=33,999%c |
|---|---|---|---|
| Maternal age, years | |||
| 15–19 | 5.8 | 5.1 | 4.4 |
| 20–24 | 16.9 | 16.4 | 16.8 |
| 25–29 | 30.0 | 29.6 | 30.9 |
| 30–34 | 29.7 | 29.4 | 30.7 |
| 35–39 | 14.5 | 15.7 | 14.1 |
| 40–44 | 2.9 | 3.7 | 2.8 |
| 45–49 | 0.1 | 0.2 | 0.1 |
| Maternal age, mean (SD), years | 29.0 (5.7) | 29.3 (5.8) | 29.1 (5.5) |
| Maternal race/ethnicity | |||
| Non-Hispanic White | 49.4 | 58.7 | 61.6 |
| Hispanic White | 21.0 | 16.7 | 15.3 |
| Asian | 10.5 | 7.1 | 7.1 |
| Black | 7.8 | 9.3 | 8.7 |
| Other | 11.3 | 8.2 | 7.3 |
| Nulliparous | 47.3 | 57.6 | 39.2 |
| Gestational age, completed weeks | |||
| 35–38 | 26.8 | 23.6 | 22.1 |
| 39 | 30.1 | 17.6 | 32.3 |
| 40 | 32.3 | 18.1 | 45.6 |
| 41+ | 10.8 | 40.6 | 0.0 |
| Gestational age, mean (SD), weeks | 39.2 (2.0) | 39.6 (2.1) | 39.1 (1.0) |
| Maternal education | |||
| <High school | 9.7 | 7.4 | 7.2 |
| High school graduate/some college | 59.6 | 62.1 | 63.1 |
| College graduate or above | 30.8 | 30.3 | 29.7 |
| Insurance status | |||
| Medicaid | 5.8 | 5.9 | 6.1 |
| Other insurance | 94.2 | 94.1 | 93.9 |
| Diabetes | 6.4 | 15.9 | 0.0 |
| Hypertension, chronic | 2.3 | 10.0 | 0.0 |
| Gestational hypertension or pre-eclampsia | 6.2 | 30.4 | 0.0 |
| Infant birth weight, g | |||
| <2500 | 2.2 | 4.9 | 1.2 |
| 2500–3499 | 54.8 | 45.4 | 48.5 |
| 3500–3999 | 31.9 | 33.0 | 35.9 |
| 4000+ | 11.0 | 16.6 | 14.4 |
| Birth weight, mean (SD), g | 3,429 (472) | 3,477 (560) | 3,516 (442) |
Population is the restricted cohort (women without contraindications to induction; see Fig. 1 for a list of contraindications). All values are % unless otherwise indicated. Percentages are of non-missing values. Less than 5% of data were missing for all characteristics except for race, which was missing for 9.9% of deliveries (10.3% of non-induced deliveries, 9.5% of medically indicated inductions, and 8.3% of elective inductions). The high proportion of missing data for race is due to changes in birth certificate race coding affecting one large site in 2007. Results changed little in a sensitivity analysis imputing that site's 2007 racial distribution was based on its 2006 data.
p-values were calculated using chi-squared tests for categorical variables and analysis of variance for continuous variables; p <0.001 for all comparisons.
Elective induction was defined as induction between 35 and 40 completed weeks' gestation without documentation of an indication from Table 2.