Table 1. Basic characteristics of the study population.
| Characteristics | Total | Singleton | Twins |
|
Abbreviations: ART, assisted reproductive technology; SD, standard deviation; BMI, body mass index; PTB, preterm birth; HDP, hypertensive disorders in pregnancy. | |||
| Maternal characteristics ( n) | 2837 | 2576 | 261 |
| Mode of conception [ n (%)] | |||
| Spontaneous | 1587 (55.9) | 1579 (61.3) | 8 (3.1) |
| ART | 1250 (44.1) | 997 (38.7) | 253 (96.9) |
| Center [ n (%)] | |||
| Nanjing | 1631 (57.5) | 1497 (58.1) | 134 (51.3) |
| Suzhou | 1206 (42.5) | 1079 (41.9) | 127 (48.7) |
| Maternal age (years, mean±SD) | 31.17±3.81 | 31.16±3.88 | 31.20±3.09 |
| Pre-pregnancy BMI [kg/m 2, n (%)] | |||
| <18.5 kg/m 2 | 287 (10.1) | 269 (10.4) | 18 (6.9) |
| [18.5, 24.0) kg/m 2 | 1939 (68.4) | 1763 (68.5) | 176 (67.4) |
| ≥24.0 kg/m 2 | 610 (21.5) | 543 (21.1) | 67 (25.7) |
| Missing | 1 (0.0) | 1 (0.0) | 0 |
| Maternal education [ n (%)] | |||
| <12 years | 459 (16.2) | 396 (15.4) | 63 (24.1) |
| ≥12 years | 2378 (83.8) | 2180 (84.6) | 198 (75.9) |
| Parity [ n (%)] | |||
| Nulliparous | 2243 (79.1) | 2008 (77.9) | 235 (90.0) |
| Multiparous | 550 (19.4) | 532 (20.7) | 18 (6.9) |
| Missing | 44 (1.5) | 36 (1.4) | 8 (3.1) |
| Diabetes in pregnancy [ n (%)] | |||
| No | 1874 (66.0) | 1714 (66.5) | 160 (61.3) |
| Yes | 961 (33.9) | 860 (33.4) | 101 (38.7) |
| Missing | 2 (0.1) | 2 (0.1) | 0 |
| Gestational age (weeks, mean±SD) | 39.16±1.62 | 39.44±1.34 | 36.43±1.63 |
| PTB [ n (%)] | |||
| No | 2 598 (91.6) | 2 463 (95.6) | 135 (51.7) |
| Yes | 239 (8.4) | 113 (4.4) | 126 (48.3) |
| HDP [ n (%)] | 220 (7.7) | 162 (6.3) | 58 (22.2) |
| Chronic hypertension | 46 (1.6) | 41 (1.6) | 5 (1.9) |
| Gestational hypertension | 71 (2.5) | 55 (2.1) | 16 (6.1) |
| Preeclampsia | 103 (3.6) | 66 (2.6) | 37 (14.2) |
| Infant characteristics ( n) | 3 083 | 2 576 | 507 |
| Birth weight (g, mean±SD) | 3251.98±538.86 | 3387.28±446.95 | 2565.27±431.20 |
| Infant sex [ n (%)] | |||
| Boys | 1 629 (52.8) | 1 367 (53.1) | 262 (51.7) |
| Girls | 1454 (47.2) | 1209 (46.9) | 245 (48.3) |
| Duration of breastfeeding [ n (%)] | |||
| <6 months | 630 (20.4) | 424 (16.5) | 206 (40.6) |
| 6–12 months | 2445 (79.3) | 2146 (83.3) | 299 (59.0) |
| Missing | 8 (0.3) | 6 (0.2) | 2 (0.4) |
| Examination age of infant (days,
mean±SD) |
365.04±7.82 | 364.91±7.82 | 365.70±7.82 |