Table 1. Characteristics associated with having a short interpregnancy interval*.
| Index births (n=3,005) | Bivariate | Multivariable | ||||
|---|---|---|---|---|---|---|
|
| ||||||
| Short interpregnancy interval (%)† | Hazard Ratio | (95% CI) | Hazard Ratio‡ | (95% CI) | ||
| Age at delivery, years | ||||||
| 15-24 | 1,202 | 20.2 | 2.91 | (1.91 - 4.45)‡ | 2.37 | (1.42 - 3.96)‡ |
| 25-29 | 882 | 15.3 | 1.99 | (1.29 - 3.05)‡ | 1.86 | (1.20 - 2.90)‡ |
| 30-34 | 594 | 8.2 | 1.00 | ref | 1.00 | ref |
| 35-44 | 327 | 8.0 | 0.98 | (0.56 - 1.73) | 0.98 | (0.56 - 1.71) |
| Parity at delivery | ||||||
| 1 child | 1,094 | 20.0 | 1.72 | (1.17 - 2.54)‡ | 1.30 | (0.87 - 1.95) |
| 2 children | 957 | 12.0 | 1.00 | ref | 1.00 | ref |
| 3 children or more | 954 | 10.1 | 0.90 | (0.57 - 1.41) | 1.17 | (0.73 - 1.87) |
| Race/ethnicity | ||||||
| White | 1,298 | 14.5 | 1.00 | ref | 1.00 | ref |
| Black | 696 | 16.2 | 1.21 | (0.85 - 1.73) | 0.96 | (0.68 - 1.34) |
| Latina | 783 | 13.0 | 0.95 | (0.67 - 1.33) | 0.84 | (0.58 - 1.21) |
| Other | 228 | 13.4 | 0.90 | (0.53 - 1.53) | 0.80 | (0.48 - 1.33) |
| Marital status at delivery | ||||||
| Single | 767 | 15.0 | 1.18 | (0.87 - 1.59) | 0.73 | (0.54 - 0.98)‡ |
| Married/cohabiting | 2,238 | 14.2 | 1.00 | ref | 1.00 | ref |
| Educational attainment | ||||||
| Less than high school | 863 | 19.2 | 1.53 | (1.13 - 2.06)‡ | 1.36 | (1.01 - 1.83)‡ |
| High school/some college | 1,371 | 13.0 | 1.00 | ref | 1.00 | ref |
| College degree | 771 | 12.7 | 0.88 | (0.62 - 1.24) | 1.12 | (0.75 - 1.66) |
| Payment for delivery | ||||||
| Private | 1,362 | 12.6 | 1.00 | ref | 1.00 | ref |
| Medicaid | 1,643 | 16.4 | 1.49 | (1.13 - 1.96)‡ | 1.18 | (0.83 - 1.69) |
| Contraceptive method§ | ||||||
| Sterilization, LARC | 621 | 0.5 | 1.00 | ref | 1.00 | ref |
| Hormonals | 724 | 12.6 | 26.5 | (8.00 - 87.6)‡ | 21.2 | (6.17 - 72.8 ‡ |
| Less effective | 746 | 17.8 | 38.6 | (10.5 - 141)‡ | 34.8 | (9.26 - 131)‡ |
| None | 914 | 23.0 | 50.0 | (14.5 - 172)‡ | 43.2 | (12.3 - 152)‡ |
These results are from our own calculations using the NSFG 2006–2010. See http://www.cdc.gov/nchs/nsfg/nsfg_2006_2010_puf.htm for more information.CI: confidence interval
Short interpregnancy interval pregnancies were conceived ≤18 months after the index birth (i.e., a live singleton birth that occurred within 3 years of the survey date [n=434]).
Percentages are weighted to reflect the sampling design of the NSFG.
p < 0.05. The p-value is based on Cox proportional hazard regression models.
Contraceptive method used at the last observed interval after delivery. Sterilization includes female sterilization and vasectomy. LARC (long-acting reversible contraception) includes intrauterine device and contraceptive implant. Hormonal methods include oral contraceptive pills, injectables, hormonal patch, and vaginal ring. Less effective methods include diaphragm, male or female condoms, withdrawal, and rhythm method.