Table 1.
Description of study population
| (N, pairs) | Birth | Embryo state in 1st and 2nd pregnancies | |||
|---|---|---|---|---|---|
| Order | Fresh/fresh | Fresh/frozen | Frozen/fresh | Frozen/frozen | |
| (3241) | (3371) | (310) | (873) | ||
| Woman’s age (mean years, SD) | 1 | 33.4 (3.8) | 32.5 (3.7) | 33.0 (3.5) | 32.7 (3.7) |
| 2 | 36.0 (3.7) | 35.0 (3.7) | 35.6 (3.4) | 35.2 (3.8) | |
| Woman’s race/ethnicity (%) White | 82.1 | 79.7 | 79.1 | 78.0 | |
| Black | 3.3 | 3.9 | 4.3 | 4.5 | |
| Hispanic | 4.3 | 5.7 | 4.3 | 4.3 | |
| Asian | 8.6 | 8.8 | 10.2 | 10.8 | |
| Hawaiian | 0.2 | 0.2 | 1.1 | 0.2 | |
| Mixed | 1.5 | 1.3 | 1.1 | 2.0 | |
| Native American | 0.0 | 0.3 | 0.0 | 0.2 | |
| (Unknown/not reported) | 37.1 | 33.9 | 39.7 | 41.6 | |
| BMI (weight/height2, mean, SD) | 1 | 24.6 (5.2) | 24.4 (4.9) | 24.2 (4.2) | 24.8 (5.1) |
| 2 | 24.8 (5.2) | 24.6 (5.1) | 24.6 (4.7) | 24.7 (5.1) | |
| Parity:% nulliparous | 1 | 89.1 | 88.6 | 85.8 | 91.4 |
| % parity = 1 | 2 | 86.5 | 86.6 | 83.5 | 90.0 |
| Blastocyst (%)a | 1, 2 | 36.3 | 67.0 | 35.2 | 55.3 |
| # embryos transferred (mean, SD) | 1 | 2.3 (0.9) | 1.9 (0.7) | 2.2 (0.7) | 2.1 (0.6) |
| 2 | 2.4 (1.0) | 1.8 (0.7) | 2.3 (0.9) | 1.8 (0.7) | |
aSiblings were matched on embryo stage