Table 1.
Baseline Characteristics of the Mothers of Mixed-Gender Twins.
| Maternal characteristics | |
|---|---|
| Maternal Race (n, %) | |
| White | 84,215 (78.0) |
| Black | 20,382 (18.9) |
| Others | 3441 (3.2) |
| Maternal age (Mean, SD) | 29.5 (6.0) |
| Maternal smoking status during pregnancy (n, %) | |
| No smoking | 78979 (73.1) |
| Smoking | 9867 (9.1) |
| Unknown | 19192 (17.8) |
| Maternal education (n, %) | |
| <12y | 15,162 (14.0) |
| 12–15y | 56,540 (52.3) |
| >15y | 34,583 (32.0) |
| Unknown | 1753 (1.6) |
| Marital status (n, %) | |
| Married | 78,599 (72.8) |
| Unmarried | 29073 (26.9) |
| Unknown | 366 (0.3) |
| Weight gain during pregnancy (Kg) | 16.6 (7.2) |
| Parity | |
| 0 | 42,798 (39.6) |
| ≥1 | 65,240 (60.4) |
| Pregnant complications1 (n, %) | 19,949 (18.5) |
| Labor complications2(n, %) | 14,892 (13.8) |
| Methods of delivery (n, %) | |
| Cesarean section | 68,256 (63.2) |
| Vaginal | 27989 (25.9) |
| Vaginal to Cesarean section3 | 4714 (4.4) |
| Unknown | 7079 (6.6) |
1Defined as one or more of the following diseases or conditions: anemia (HCT <30 or Hb <100 g/L), cardiac disease; acute or chronic lung disease, diabetes, hydramnios or oligohydramnios, hemoglobinophathy, chronic or pregnancy-associated hypertension, and renal disease. 2Defined as one or more of the following diseases or conditions: premature rupture or membrane >12 hours, abruption placenta, placenta previa, precipitous or prolong labor, dysfunctional labor, seizure during labor, cephalopelvic disproportion, and excessive bleeding. 3The first babies were vaginal delivery and the second ones by cesarean section.