Table 1.
Maternal and Paternal Demographic Characteristics by Maternal Fertility Group and Infant Gender Combinations
| All Twins | Like Gender Pairs | Unlike Gender Pairs | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| All Groups | Fertile | Subfertile | IVF | Fertile | Subfertile | IVF | Fertile | Subfertile | IVF | ||
| N, pregnancies | 10,352 | 6,090 | 724 | 3,538 | 4,150 | 391 | 1,817 | 1,940 | 333 | 1,721 | |
| Maternal | Mean (SD) | 32.3 (5.8) | 30.4 (5.7) | 34.2 (4.5) | 35.3 (4.6) | 30.1 (5.7) | 34.6 (4.4) | 35.4 (4.6) | 30.9 (5.5) | 33.7 (4.6) | 35.3 (4.6) |
| Age (years) | (%) <35 | 63.1 | 75.1 | 54.4 | 44.4 | 76.5 | 51.4 | 43.6 | 72.1 | 58.0 | 45.1 |
| 35–37 | 19.5 | 15.7 | 23.2 | 25.4 | 14.6 | 23.3 | 24.8 | 18.1 | 23.1 | 26.0 | |
| 38–40 | 11.2 | 7.1 | 15.3 | 17.5 | 6.8 | 16.9 | 18.6 | 7.7 | 13.5 | 16.3 | |
| 41–42 | 3.2 | 1.4 | 3.9 | 6.3 | 1.4 | 4.4 | 6.8 | 1.4 | 3.3 | 5.8 | |
| ≥43 | 2.9 | 0.7 | 3.2 | 6.5 | 0.7 | 4.1 | 6.2 | 0.8 | 2.1 | 6.8 | |
| Paternal | Mean, SD | 34.9 (6.5) | 33.1 (6.5) | 36.6 (5.7) | 37.4 (5.8) | 32.9 (6.5) | 36.9 (5.9) | 37.5 (5.9) | 33.6 (6.4) | 36.2 (5.6) | 37.3 (5.7) |
| Age (years) | (%) <35 | 48.6 | 59.5 | 39.4 | 33.1 | 60.9 | 38.0 | 32.4 | 56.6 | 41.0 | 33.8 |
| 35–37 | 20.7 | 18.6 | 23.1 | 23.6 | 18.4 | 20.8 | 22.1 | 19.0 | 25.7 | 25.2 | |
| 38–40 | 13.5 | 10.5 | 16.7 | 17.6 | 9.9 | 18.5 | 18.6 | 11.6 | 14.7 | 16.6 | |
| 41–42 | 6.4 | 4.7 | 7.9 | 8.7 | 4.4 | 7.8 | 9.4 | 5.3 | 8.0 | 8.0 | |
| ≥43 | 10.8 | 6.7 | 12.9 | 16.9 | 6.4 | 14.8 | 17.5 | 7.5 | 10.7 | 16.3 | |
| Maternal Race | Hispanic | 8.7 | 12.3 | 3.0 | 3.6 | 12.6 | 3.3 | 3.4 | 11.6 | 2.7 | 3.9 |
| & Ethnicity (%) | White | 76.6 | 69.8 | 87.7 | 85.9 | 69.2 | 88.0 | 86.2 | 71.2 | 87.4 | 85.5 |
| Black | 7.4 | 10.7 | 2.2 | 2.9 | 10.5 | 1.5 | 2.9 | 11.3 | 3.0 | 2.8 | |
| Asian | 5.5 | 4.8 | 5.7 | 6.5 | 5.4 | 5.4 | 6.4 | 3.6 | 6.0 | 6.7 | |
| Other | 1.9 | 2.4 | 1.4 | 1.1 | 2.4 | 1.8 | 1.1 | 2.4 | 0.9 | 1.1 | |
| Paternal Race | Hispanic | 8.0 | 11.7 | 3.5 | 3.2 | 12.5 | 3.9 | 2.9 | 9.8 | 3.1 | 3.4 |
| & Ethnicity (%) | White | 77.9 | 71.1 | 87.2 | 86.8 | 69.7 | 87.8 | 87.2 | 74.2 | 86.5 | 86.3 |
| Black | 7.4 | 10.6 | 2.5 | 3.2 | 10.6 | 1.8 | 3.1 | 10.5 | 3.4 | 3.3 | |
| Asian | 5.1 | 4.6 | 5.5 | 5.8 | 5.1 | 5.2 | 5.8 | 3.5 | 5.8 | 5.8 | |
| Other | 1.7 | 2.1 | 1.3 | 1.0 | 2.2 | 1.3 | .9 | 1.9 | 1.2 | 1.1 | |
| Maternal | <HS or HS/GED | 23.5 | 33.4 | 11.5 | 8.8 | 33.6 | 10.5 | 9.3 | 33.1 | 12.7 | 8.3 |
| Education (%) | Some College | 19.6 | 22.0 | 16.0 | 16.1 | 22.7 | 15.6 | 15.0 | 20.5 | 16.6 | 17.3 |
| BS or Graduate | 56.9 | 44.6 | 72.5 | 75.1 | 43.7 | 73.9 | 75.7 | 46.4 | 70.8 | 74.4 | |
| Paternal | <HS or HS/GED | 28.8 | 38.5 | 18.7 | 15.1 | 39.4 | 19.2 | 15.2 | 36.6 | 18.1 | 15.1 |
| Education (%) | Some College | 15.6 | 17.7 | 12.5 | 12.9 | 17.8 | 11.7 | 12.4 | 17.7 | 13.5 | 13.3 |
| BS or Graduate | 55.6 | 43.7 | 68.8 | 72.0 | 42.8 | 69.1 | 72.4 | 45.7 | 68.4 | 71.6 | |
| Maternal | Yes | 4.4 | 7.0 | 1.0 | 0.7 | 6.2 | 1.3 | 0.7 | 8.6 | 0.6 | 0.6 |
| Smoking (%) | No | 95.6 | 93.0 | 99.0 | 99.4 | 93.8 | 98.7 | 99.3 | 91.4 | 99.4 | 99.4 |
| Payor | Private | 74.0 | 59.6 | 93.7 | 94.7 | 60.0 | 93.4 | 94.2 | 58.8 | 94.0 | 95.2 |
| Source (%) | Public | 24.3 | 38.6 | 5.4 | 3.4 | 38.4 | 5.9 | 3.6 | 39.0 | 4.8 | 3.1 |
| Self-pay or Free | 1.8 | 1.8 | 1.0 | 1.9 | 1.6 | 0.8 | 2.2 | 2.2 | 1.2 | 1.6 | |
All comparisons across fertility groups were significant at p<0.0001