Table. Maternal Characteristics of Singleton and Twin Pregnancies Stratified by Cervical Length Clustering Subgroup.
| Maternal characteristic | Singleton pregnancies, No. (%) | Twin pregnancies, No. (%) | ||||
|---|---|---|---|---|---|---|
| All (n = 41 706) | Cervical length | All (n = 1853) | Cervical length | |||
| Stable (n = 20 340) | Shortened (n = 21 366) | Stable (n = 1307) | Shortened (n = 546) | |||
| Age, mean (SD), y | 33.0 (4.0) | 33.6 (4.0) | 32.5 (3.9) | 33.3 (3.6) | 33.5 (3.7) | 32.9 (3.5) |
| ≤35 | 29 230 (70.1) | 13 276 (65.3) | 15 954 (74.7) | 1266 (68.3) | 862 (66.0) | 404 (74.0) |
| >35 | 12 476 (29.9) | 7064 (34.7) | 5412 (25.3) | 587 (31.7) | 445 (34.1) | 142 (26.0) |
| Height, mean (SD), cm | 162.5 (5.2) | 162.5 (5.3) | 162.5 (5.0) | 162.9 (5.1) | 162.8 (5.1) | 162.9 (5.2) |
| Prepregnancy weight, mean (SD), kg | 58.5 (9.0) | 59.8 (9.3) | 57.3 (8.6) | 59.7 (9.1) | 60.1 (9.2) | 58.8 (9.0) |
| Prepregnancy BMI, mean (SD)a | 22.1 (3.2) | 22.6 (3.3) | 21.7 (3.0) | 22.5 (3.2) | 22.7 (3.2) | 22.2 (3.3) |
| Underweight | 3787 (9.1) | 1311 (6.5) | 2476 (11.6) | 136 (7.3) | 84 (6.4) | 52 (9.5) |
| Normal weight | 28 192 (67.6) | 13 332 (65.6) | 14 860 (69.6) | 1202 (64.9) | 841 (64.4) | 361 (66.1) |
| Overweight | 7459 (17.9) | 4319 (21.2) | 3140 (14.7) | 398 (21.5) | 295 (22.6) | 103 (18.9) |
| Obesity | 2268 (5.4) | 1378 (6.8) | 890 (4.2) | 117 (6.3) | 87 (6.7) | 30 (5.5) |
| Gestational weight gain, mean (SD), kg | 13.01 (4.4) | 13.15 (4.5) | 12.88 (4.3) | 15.73 (5.2) | 16.03 (5.2) | 15.01 (5.1) |
| Parity | ||||||
| Primipara | 29 370 (70.4) | 13 092 (64.4) | 16 278 (76.2) | 1544 (83.3) | 1056 (80.8) | 488 (89.4) |
| Multipara | 12 336 (29.6) | 7248 (35.6) | 5088 (23.8) | 309 (16.7) | 251 (19.2) | 58 (10.6) |
| Conception mode | ||||||
| Spontaneous | 37 230 (89.3) | 18 066 (88.8) | 19 164 (89.7) | 743 (40.1) | 571 (43.7) | 172 (31.5) |
| ART | 4476 (10.7) | 2274 (11.2) | 2202 (10.3) | 1110 (59.9) | 736 (56.3) | 374 (68.5) |
| Gestational diabetes | ||||||
| No | 30 718 (73.7) | 14 920 (73.4) | 15 798 (73.9) | 1325 (71.5) | 959 (73.4) | 366 (67.0) |
| Yes | 10 988 (26.4) | 5420 (26.7) | 5568 (26.1) | 528 (28.5) | 348 (26.6) | 180 (33.0) |
| Hypertensive disorders of pregnancy | ||||||
| No | 38 413 (92.1) | 18 530 (91.1) | 19 883 (93.1) | 1643 (88.7) | 1167 (89.3) | 476 (87.2) |
| Yes | 3293 (7.9) | 1810 (8.9) | 1483 (6.9) | 210 (11.3) | 140 (10.7) | 70 (12.8) |
| Preeclampsia | ||||||
| No | 40 337 (96.7) | 19 571 (96.2) | 20 766 (97.2) | 1726 (93.2) | 1226 (93.8) | 500 (91.6) |
| Yes | 1369 (3.3) | 769 (3.8) | 600 (2.8) | 127 (6.9) | 81 (6.2) | 46 (8.4) |
| Gestational age at delivery, mean (SD), wk | 39.2 (1.3) | 39.3 (1.2) | 39.2 (1.4) | 36.8 (2.0) | 37.2 (1.7) | 36.0 (2.3) |
| sPTB | ||||||
| No | 40 275 (96.6) | 19 793 (97.3) | 20 482 (95.9) | 1386 (74.8) | 1069 (81.8) | 317 (58.1) |
| Yes | 1431 (3.4) | 547 (2.7) | 884 (4.1) | 467 (25.2) | 238 (18.2) | 229 (41.9) |
| Subtype of sPTB | ||||||
| Moderate to late preterm birth | 1255 (3.0) | 490 (2.4) | 765 (3.6) | 399 (21.5) | 204 (15.6) | 195 (35.7) |
| Early preterm birth | 176 (0.4) | 57 (0.3) | 119 (0.6) | 68 (3.7) | 34 (2.6) | 34 (6.2) |
Abbreviations: ART, assisted reproductive technology; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); sPTB, spontaneous preterm birth.
a
Underweight: BMI less than 18.5; normal weight: BMI 18.5 to less than 24.0; overweight: BMI greater than or equal to 24.0 to less than 28.0; obesity: BMI greater than or equal to 28.0.