Table 1.
Maternal and Infant Characteristics Among Singletons and Twins Born at 24 Weeks of Gestation or Later, United States, 1995-96 and 2004-05
| Maternal characteristics* | Singletons | Twins | ||||
|---|---|---|---|---|---|---|
| 1995-96 | 2004-05 | Odds ratio (95%CI) | 1995-96 | 2004-05 | Odds ratio (95%CI) | |
| No. of women | 6,359,866 | 6,122,022 | 82,639 | 101,572 | ||
| Age (years) <20 | 13.3 | 10.6 | 0.77 (0.77-0.77) | 7.24 | 5.14 | 0.70 (0.68-0.71) |
| 20-24 | 24.8 | 25.8 | 1.06 (1.05-1.06) | 19.6 | 18.0 | 0.90 (0.89-0.92) |
| 25-29 | 27.5 | 27.4 | 0.99 (0.99-1.00) | 27.7 | 26.1 | 0.92 (0.91-0.92) |
| 30-34 | 23.0 | 22.7 | 0.98 (0.98-0.99) | 28.9 | 29.1 | 1.01 (1.00-1.03) |
| 35-39 | 9.72 | 11.0 | 1.15 (1.15-1.15) | 14.2 | 16.9 | 1.23 (1.20-1.25) |
| 40+ | 1.73 | 2.45 | 1.43 (1.42-1.44) | 2.44 | 4.73 | 1.98 (1.91-2.06) |
| Race: Non-Hispanic white | 66.2 | 58.9 | 0.73 (0.73-0.73) | 69.2 | 65.5 | 0.84 (0.83-0.85) |
| African American | 16.5 | 15.4 | 0.93 (0.92-0.93) | 18.1 | 16.8 | 0.91 (0.90-0.93) |
| Hispanic | 13.3 | 20.2 | 1.64 (1.64-1.65) | 9.81 | 13.4 | 1.42 (1.39-1.45) |
| Other | 4.04 | 5.56 | 1.40 (1.39-1.41) | 2.89 | 4.31 | 1.51 (1.46-1.57) |
| Maternal education <12 years | 20.8 | 20.6 | 0.98 (0.98-0.98) | 15.3 | 13.6 | 0.84 (0.83-0.86) |
| Smoking during pregnancy | 13.8 | 11.1 | 0.78 (0.78-0.78) | 12.4 | 9.00 | 0.70 (0.68-0.71) |
| Unmarried | 32.4 | 36.8 | 1.22 (1.21-1.22) | 27.9 | 28.6 | 1.03 (1.02-1.05) |
| No prior live births | 42.3 | 40.4 | 0.93 (0.92-0.93) | 21.9 | 22.4 | 1.02 (1.01-1.04) |
| Infant sex (male) | 51.2 | 51.2 | 1.00 (1.00-1.00) | 49.9 | 50.2 | 1.01 (1.00-1.02) |
| Congenital anomalies (yes) | 1.59 | 1.17 | 0.74 (0.73-0.74) | 2.44 | 1.66 | 0.69 (0.66-0.72) |
| Gestational age-specific | ||||||
| Stillbirths: 24-27 wks | 13.4 | 11.6 | 0.85 (0.81-0.90) | 6.16 | 4.66 | 0.74 (0.64-0.87) |
| 28-31 | 7.78 | 6.91 | 0.88 (0.84-0.92) | 3.10 | 1.89 | 0.60 (0.51-0.70) |
| 32-33 | 4.19 | 3.51 | 0.83 (0.78-0.88) | 1.26 | 0.59 | 0.47 (0.37-0.59) |
| 34-36 | 1.21 | 0.95 | 0.78 (0.74-0.81) | 0.51 | 0.28 | 0.54 (0.45-0.63) |
| > = 37 | 0.13 | 0.11 | 0.81 (0.79-0.84) | 0.24 | 0.15 | 0.61 (0.49-0.76) |
| All | 0.34 | 0.30 | 0.88 (0.86-0.89) | 0.80 | 0.51 | 0.64 (0.59-0.69) |
| Neonatal deaths: 24-27 wks | 18.5 | 16.4 | 0.87 (0.83-0.91) | 23.0 | 18.5 | 0.76 (0.69-0.83) |
| 28-31 | 4.11 | 3.69 | 0.89 (0.84-0.95) | 3.03 | 2.54 | 0.83 (0.72-0.97) |
| 32-33 | 1.89 | 1.63 | 0.88 (0.80-0.96) | 0.71 | 0.62 | 0.86 (0.66-1.12) |
| 34-36 | 0.61 | 0.50 | 0.81 (0.77-0.87) | 0.39 | 0.25 | 0.65 (0.53-0.78) |
| > = 37 | 0.10 | 0.08 | 0.76 (0.73-0.79) | 0.20 | 0.11 | 0.55 (0.43-0.72) |
| All | 0.24 | 0.21 | 0.87 (0.85-0.89) | 1.17 | 1.95 | 0.80 (0.75-0.86) |
*Women with missing information excluded: 5-8% for smoking status and 1-5% for congenital anomalies. All proportions based on live births except for stillbirth rates which were based on total births.
All differences in maternal/infant characteristics between 1995-96 and 2004-05 were statistically significant (P < 0.05) except for the differences in infant sex and the proportion of twin births at 32-33 weeks of gestation.