Table 1.
Baseline characteristics of the study population, stratified according to quartile of neighbourhood deprivation
| Maternal characteristics | Total study population | Lowest deprivation quartile | Second deprivation quartile | Third deprivation quartile | Highest deprivation quartile | P value |
| N=8617 | n=2170 | n=2208 | n=2090 | n=2149 | ||
| Neighbourhood status score | −1.13 (1.39) | −2.96 (0.51) | −1.62 (0.31) | −0.51 (0.37) | 0.61 (0.49) | <0.001 |
| Age at intake (years) | 29.6 (5.3) | 28.1 (5.5) | 28.7 (5.7) | 30.2 (4.9) | 31.6 (4.1) | <0.001 |
| ≤18, n (%) | 83 (1.0) | 33 (1.5) | 35 (1.6) | 12 (0.6) | 3 (0.1) | |
| >18 and ≤35, n (%) | 7256 (84.2) | 1888 (87.0) | 1867 (84.6) | 1760 (84.2) | 1741 (81.0) | |
| >35, n (%) | 1278 (14.8) | 249 (11.5) | 306 (13.8) | 318 (15.2) | 405 (18.9) | |
| Prepregnancy body mass index (kg/m2) | 22.8 (18.4–32.2) | 23.5 (18.0–33.6) | 23.0 (18.1–32.5) | 22.9 (18.2–32.0) | 22.3 (18.5–30.1) | <0.001 |
| ≤18.5, n (%) | 492 (5.7) | 122 (5.6) | 139 (6.3) | 118 (5.6) | 112 (5.2) | |
| >18.5 and ≤25, n (%) | 5436 (63.0) | 1233 (56.8) | 1343 (60.8) | 1315 (62.9) | 1546 (71.9) | |
| >25, n (%) | 2689 (31.3) | 815 (37.6) | 726 (32.9) | 657 (31.4) | 491 (22.8) | |
| Parity (nulliparous) | 4796 (55.7) | 1090 (50.2) | 1273 (57.7) | 1227 (58.7) | 1205 (56.1) | <0.001 |
| Educational level, n (%) | <0.001 | |||||
| Lower/no | 1101 (12.8) | 503 (23.2) | 366 (16.5) | 179 (8.5) | 52 (2.4) | |
| Middle | 4060 (47.1) | 1153 (53.1) | 1152 (52.2) | 1007 (48.2) | 747 (34.8) | |
| High | 3456 (40.1) | 514 (23.7) | 690 (31.3) | 904 (43.3) | 1349 (62.8) | |
| Ethnicity, n (%) | <0.001 | |||||
| Dutch and Western | 4967 (57.6) | 636 (29.3) | 1084 (49.1) | 1426 (68.2) | 1821 (84.7) | |
| Turkish and Moroccan | 1464 (17.0) | 714 (32.9) | 471 (21.3) | 222 (10.6) | 57 (2.7) | |
| African | 1178 (13.7) | 519 (23.9) | 370 (16.8) | 211 (10.1) | 78 (3.6) | |
| Asian | 1008 (11.7) | 301 (13.9) | 283 (12.8) | 231 (11.1) | 193 (9.0) | |
| Smoking, n (%) | <0.001 | |||||
| Never smoked during pregnancy | 6256 (72.6) | 1515 (69.8) | 1523 (69.0) | 1518 (72.6) | 1700 (79.1) | |
| Smoked until pregnancy was known | 735 (8.5) | 171 (7.9) | 183 (8.3) | 188 (9.0) | 193 (9.0) | |
| Continued smoking in pregnancy | 1626 (18.9) | 484 (22.3) | 502 (22.7) | 384 (18.4) | 256 (11.9) | |
| Alcohol, n (%) | <0.001 | |||||
| No alcohol consumption in pregnancy | 4351 (50.5) | 1436 (66.2) | 1200 (54.4) | 990 (47.4) | 726 (33.8) | |
| Alcohol consumption until pregnancy was known | 1149 (13.3) | 220 (10.1) | 239 (10.8) | 335 (16.0) | 354 (16.5) | |
| Continued alcohol consumption in pregnancy | 3117 (36.2) | 514 (23.7) | 769 (34.8) | 765 (36.6) | 1069 (49.7) | |
| Folic acid supplement intake, n (%) | <0.001 | |||||
| None | 2751 (31.9) | 1141 (52.6) | 843 (38.2) | 534 (25.6) | 233 (10.8) | |
| Start in first 10 weeks of pregnancy | 2661 (30.9) | 594 (27.4) | 703 (31.8) | 650 (31.1) | 714 (33.2) | |
| Start preconceptionally | 3205 (37.2) | 435 (20.0) | 662 (30.0) | 906 (43.3) | 1202 (55.9) | |
| Hypertension, n (%) | 0.11 | |||||
| Pregnancy-induced hypertension | 311 (3.6) | 69 (3.2) | 80 (3.6) | 74 (3.5) | 88 (4.1) | |
| Pre-eclampsia | 142 (1.6) | 54 (2.5) | 36 (1.6) | 29 (1.4) | 23 (1.1) | |
| HELLP | 29 (0.3) | 4 (0.2) | 9 (0.4) | 8 (0.4) | 8 (0.4) | |
| Gestational diabetes | 89 (1.0) | 21 (1.0) | 32 (1.4) | 24 (1.1) | 12 (0.6) | 0.03 |
| Birth weight (g), n (%) | <0.01 | |||||
| ≤2500 | 431 (5.0) | 118 (5.4) | 135 (6.1) | 110 (5.3) | 68 (3.2) | |
| >2500 and ≤4000 | 7017 (81.4) | 1815 (83.6) | 1786 (80.9) | 1683 (80.5) | 1733 (80.6) | |
| >4000 | 1169 (13.6) | 237 (11.0) | 287 (13.0) | 297 (14.2) | 348 (16.2) | |
| Gestational age at delivery (weeks), n (%) | 0.01 | |||||
| <37 | 492 (5.7) | 134 (6.2) | 152 (6.9) | 117 (5.6) | 89 (4.1) | |
| 37–42 | 7697 (89.3) | 1937 (89.3) | 1947 (88.2) | 1859 (88.9) | 1954 (90.9) | |
| >42 | 428 (5.0) | 99 (4.5) | 109 (4.9) | 114 (5.5) | 106 (5.0) | |
| Complications in a previous pregnancy, n (%) | 606 (7.0) | 153 (7.1) | 149 (6.7) | 132 (6.3) | 172 (8.0) | 0.13 |
| Fetal sex (male) | 4347 (50.4) | 1063 (49.0) | 1147 (51.9) | 1066 (51.0) | 1071 (49.8) | 0.22 |
Data are presented as n (%), mean (SD) or median with the 90% range.
P-value in bold: statistically significant p-value<0.05.
Differences in baseline characteristics were tested using analysis of variance, Kruskal-Wallis test and χ2 test.
Confounders are imputed. Non-imputed percentages are valid percentages.
HELLP, Hemolysis, elevated liver enzymes and low platelets syndrome.