Table 3.
Pregnancy, Birth, and Infant Outcomes by Maternal Fertility Group and Infant Gender Combinations
| All Twins | Like Gender Pairs | Unlike Gender Pairs | P Values | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All Groups | Fertile | Subfertile | IVF | Fertile | Subfertile | IVF | Fertile | Subfertile | IVF | Across Groups | ||||
| N, pregnancies | 10,352 | 6,090 | 724 | 3,538 | 4,150 | 391 | 1,817 | 1,940 | 333 | 1,721 | ||||
| N, infants | 20,703 | 12,179 | 1,448 | 7,076 | 8,300 | 782 | 3,634 | 3,879 | 666 | 3,442 | All | Like | Unlike | |
| Groups | All | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 1–2–3 | 4–5–6 | 7–8–9 | |
| Pre-existing | Diabetes (%) | 1.9 | 1.7 | 2.4 | 2.2 | 1.8 | 2.3 | 2.6 | 1.5 | 2.4 | 1.7 | NS | NS | NS |
| Conditions | Chronic hypertension (%) | 2.8 | 2.6 | 2.9 | 3.2 | 2.5 | 2.8 | 2.9 | 2.6 | 3.0 | 3.4 | NS | NS | NS |
| Parity | Nulliparous (%) | 25.5 | 20.9 | 28.8 | 32.2 | 20.9 | 29.2 | 32.6 | 20.7 | 28.0 | 32.0 | *** | *** | *** |
| Pregnancy | Gestational diabetes (%) | 9.2 | 8.1 | 11.6 | 10.7 | 8.3 | 10.0 | 10.3 | 7.6 | 13.5 | 11.0 | *** | * | *** |
| Conditions | Pregnancy hypertension (%) | 22.7 | 20.5 | 26.7 | 25.5 | 20.1 | 28.4 | 25.3 | 21.4 | 24.6 | 25.6 | *** | *** | ** |
| Prenatal hospitalization (%) | 16.2 | 15.8 | 17.4 | 16.5 | 16.3 | 16.1 | 17.1 | 14.8 | 18.9 | 16.0 | NS | NS | NS | |
| Uterine bleeding (%) | 1.7 | 1.0 | 1.9 | 2.9 | 1.0 | 2.3 | 2.6 | 1.1 | 1.5 | 3.2 | *** | *** | *** | |
| Labor and | Breech/Malpresentation (%) | 31.6 | 30.5 | 28.4 | 34.0 | 29.2 | 26.4 | 32.3 | 33.3 | 30.6 | 35.7 | ** | * | NS |
| Delivery | Cephalopelvic Disproportion (%) | 0.9 | 0.8 | 1.2 | 1.0 | 0.9 | 1.3 | 1.2 | 0.7 | 1.2 | 0.9 | NS | NS | NS |
| Factors | Abruptio placenta (%) | 2.5 | 2.2 | 3.7 | 2.8 | 2.2 | 3.8 | 2.8 | 2.3 | 3.6 | 2.8 | * | NS | NS |
| Placenta previa (%) | 1.3 | 0.7 | 2.1 | 2.2 | 0.9 | 2.1 | 2.4 | 0.4 | 2.1 | 2.0 | *** | *** | *** | |
| Vasa previa (%) | 0.17 | 0.13 | 0.28 | 0.23 | 0.17 | 0.51 | 0.22 | 0.05 | 0.0 | 0.23 | NS | NS | NS | |
| Other excessive bleeding (%) | 1.5 | 1.2 | 2.2 | 1.8 | 1.2 | 2.8 | 2.0 | 1.0 | 1.5 | 1.7 | ** | ** | NS | |
| Placental complications1 (%) | 3.9 | 3.0 | 5.9 | 5.1 | 3.0 | 6.1 | 5.3 | 2.7 | 5.7 | 4.9 | *** | *** | ** | |
| Mode of | Vaginal2 (%) | 27.8 | 31.3 | 28.3 | 21.5 | 31.6 | 30.4 | 23.3 | 30.6 | 25.8 | 19.7 | |||
| Delivery | Primary cesarean (%) | 57.6 | 52.8 | 60.2 | 65.4 | 52.6 | 58.8 | 64.2 | 53.1 | 61.9 | 66.7 | *** | *** | *** |
| Repeat cesarean (%) | 14.6 | 15.9 | 11.5 | 13.1 | 15.7 | 10.7 | 12.6 | 16.3 | 12.3 | 13.6 | ||||
| Primary cesarean among nulliparas (%) | 73.2 | 69.0 | 68.6 | 78.7 | 67.9 | 64.9 | 76.7 | 71.5 | 73.1 | 80.8 | *** | ** | ** | |
| Birthweight | Mean g (SD) | 2,408 (613) | 2,395 (615) | 2,395 (616) | 2,431 (610) | 2,372 (618) | 2,417 (589) | 2,409 (608) | 2,446 (606) | 2,368 (646) | 2,455 (611) | ** | ** | ** |
| Very low birthweight (<1,500g, %) | 8.1 | 8.3 | 8.5 | 7.6 | 8.8 | 6.9 | 8.4 | 7.3 | 10.4 | 6.7 | NS | NS | ** | |
| Low birthweight (<2,500g, %) | 51.7 | 52.6 | 51.3 | 50.4 | 54.1 | 51.0 | 51.7 | 49.1 | 51.5 | 49.0 | * | * | NS | |
| Small-for-gestation (Zscore <−1.28, %) | 18.7 | 19.4 | 19.0 | 17.6 | 20.3 | 18.7 | 18.7 | 17.4 | 19.3 | 16.4 | ** | NS | NS | |
| Large-for-gestation (Z-score >1.28, %) | 1.3 | 1.1 | 1.9 | 1.5 | 1.2 | 1.7 | 1.5 | 1.0 | 2.1 | 1.4 | * | NS | * | |
| Gestation | Mean weeks (SD) | 35.6 (3.0) | 35.6 (3.1) | 35.5 (3.1) | 35.6 (2.9) | 35.5 (3.1) | 35.6 (3.0) | 35.5 (3.0) | 35.7 (3.0) | 35.4 (3.3) | 35.6 (2.9) | NS | NS | * |
| Early Preterm (<32 weeks, %) | 9.1 | 9.1 | 9.5 | 8.9 | 9.6 | 8.1 | 9.6 | 8.0 | 11.1 | 8.3 | NS | NS | * | |
| Preterm (<37 weeks, %) | 53.4 | 53.0 | 54.8 | 53.8 | 53.5 | 56.0 | 54.7 | 52.1 | 53.3 | 52.8 | NS | NS | NS | |
| Birth Defects | Birth Defects (%) | 2.4 | 2.3 | 2.1 | 2.7 | 2.5 | 2.1 | 2.6 | 1.8 | 2.1 | 2.8 | NS | NS | * |
| Gender | Male (%) | 50.9 | 50.8 | 49.1 | 51.5 | 51.1 | 48.3 | 52.9 | 50.0 | 50.0 | 50.0 | NS | * | NS |
| Infant Death | Infant (0–364 days, %) | 1.61 | 1.79 | 2.07 | 1.22 | 1.80 | 2.30 | 1.24 | 1.78 | 1.80 | 1.19 | ** | * | NS |
| Neonatal (0–27 days, %) | 1.42 | 1.54 | 1.93 | 1.12 | 1.61 | 2.30 | 1.16 | 1.39 | 1.50 | 1.07 | * | * | NS | |
| Postneonatal (28–364 days. %) | 0.19 | 0.25 | 0.14 | 0.10 | 0.18 | 0.00 | 0.08 | 0.39 | 0.30 | 0.12 | NS | NS | NS | |
1
Placental complications includes abruptio placenta placenta previa, and vasa previa;
2
Vaginal includes VBAC, forceps, and vacuum deliveries Significance across fertility groups, NS=not significant (≥0.05);
*
p<0.05;
**
p<0.01;
***
p<0.0001;
bolded values are significant.