Table 1.
Maternal characteristics of the full and final sample*: National Maternal and Infant Health Survey 1988, United States (Sanderson et al., 1991)
| Maternal characteristics | Full sample | Final sample | ||
|---|---|---|---|---|
| Live births n = 8384 | Stillbirths n = 2803 | Live births n = 4199 | Stillbirths n = 1375 | |
| Maternal age (years) (%) | ||||
| <20 | 12.1 | 12.5 | 11.1 | 10.7 |
| 20–24 | 27.5 | 27.4 | 25.9 | 26.3 |
| 25–29 | 31.6 | 28.5 | 33.0 | 30.6 |
| 30–34 | 20.6 | 20.0 | 21.7 | 21.4 |
| ≥35 | 8.1 | 11.1 | 8.3 | 11.0 |
| Maternal education (years) (%) | ||||
| ≤12 | 60.3 | 65.4 | 54.7 | 61.3 |
| 13–16 | 34.1 | 30.3 | 36.3 | 34.2 |
| ≥17 | 5.6 | 4.3 | 6.3 | 4.5 |
| Primiparity (%) | 30.4 | 35.0 | 31.2 | 36.4 |
| Black race (%) | 15.8 | 24.2 | 12.1 | 19.5 |
| Single marital status (%) | 25.1 | 22.0 | 20.5 | 17.8 |
| Cigarette smoking (%) | 22.0 | 24.8 | 20.9 | 23.8 |
| Alcohol use (%) | 20.9 | 15.5 | 22.5 | 15.3 |
| Cocaine use (%) | 1.7 | 1.9 | 1.2 | 2.1 |
| Marijuana use (%) | 5.5 | 6.6 | 5.4 | 6.1 |
| Iron use 3 months before pregnancy (%) | 9.2 | 9.5 | 9.2 | 8.8 |
| Iron use during pregnancy (%) | 33.0 | 33.1 | 31.2 | 32.0 |
| Pre‐pregnancy body mass index † | 22.8 (5.5) | 24.0 (5.8) | 22.8 (5.2) | 23.9 (7.0) |
| Gestational age at delivery † | 39.5 (2.7) | 35.7 (5.3) | 39.5 (2.6) | 36.0 (4.4) |
| Week prenatal care initiated † | 12.4 (9.1) | 12.4 (5.8) | 12.5 (7.1) | 12.4 (5.9) |
| Week first haemoglobin drawn † | 12.7 (5.8) | 12.4 (6.3) | ||
*
Full and final samples were restricted to women who delivered a singleton at ≥28 weeks’ gestation. The final sample is similar to the full sample, but is restricted to women for whom a haemoglobin or haematocrit measurement and smoking information were available.
†
Data expressed as mean (standard deviation).