| Characteristic | Folic acid | Pre-natal vitamins | Multivitamins or vitamin B complex | No FACSs |
| Subjects n | 1998 | 287 | 199 | 1302 |
| Males | 1035/1998 (51.8) | 143/287 (49.8) | 97/199 (48.7) | 689/1302 (52.9) |
| Region | ||||
| North | 602/1998 (30.1) | 56/287 (19.5) | 56/199 (28.1) | 459/1302 (35.3) |
| Central | 826/1998 (41.3) | 132/287 (46.0) | 73/199 (36.7) | 503/1302 (38.6) |
| West | 570/1998 (28.5) | 99/287 (34.5) | 70/199 (35.2) | 340/1302 (26.1) |
| Ethnic background | ||||
| Dutch | 1851/1925 (96.2) | 252/269 (93.7) | 170/187 (90.9) | 1148/1236 (92.9) |
| Western | 32/1925 (1.7) | 6/269 (2.2) | 7/187 (3.7) | 27/1236 (2.2) |
| Non-Western | 42/1925 (2.2) | 11/269 (4.1) | 10/187 (5.3) | 61/1236 (4.9) |
| Older siblings | ||||
| 0 | 1095/1986 (55.1) | 118/286 (41.3) | 70/197 (35.5) | 578/1290 (44.8) |
| 1 | 677/1986 (34.1) | 116/286 (40.6) | 79/197 (40.1) | 472/1290 (36.6) |
| 2 | 179/1986 (9.0) | 36/286 (12.6) | 36/197 (18.3) | 155/1290 (12.0) |
| ≥3 | 35/1986 (1.8) | 16/286 (5.6) | 12/197 (6.1) | 85/1290 (6.6) |
| Maternal smoking during pregnancy | 277/1973 (14.0) | 49/281 (17.4) | 39/198 (19.7) | 290/1288 (22.5) |
| Prematurity <37 weeks | 101/1990 (5.1) | 9/285 (3.2) | 13/198 (6.6) | 63/1292 (4.9) |
| Born by Caesarean section | 163/1976 (8.2) | 23/286 (8.0) | 23/196 (11.7) | 112/1275 (8.8) |
| Allergic mother | 637/1998 (31.9) | 85/287 (29.6) | 77/199 (38.7) | 360/1302 (27.6) |
| Allergic father | 623/1998 (31.2) | 85/287 (29.6) | 66/199 (33.2) | 385/1302 (29.6) |
| Maternal education level | ||||
| Low | 370/1973 (18.8) | 82/279 (29.4) | 42/197 (21.3) | 365/1276 (28.6) |
| Intermediate | 817/1973 (41.4) | 116/279 (41.6) | 73/197 (37.1) | 551/1276 (43.2) |
| High | 786/1973 (39.8) | 81/279 (29.0) | 82/197 (41.6) | 360/1276 (28.2) |
| Paternal education level | ||||
| Low | 439/1961 (22.4) | 77/270 (28.5) | 42/194 (21.6) | 388/1256 (30.9) |
| Intermediate | 658/1961 (33.6) | 91/270 (33.7) | 70/194 (36.1) | 449/1256 (35.7) |
| High | 864/1961 (44.1) | 102/270 (37.8) | 82/194 (42.3) | 419/1256 (33.4) |
| Smoking in the home at 1 yr of age | 460/1978 (23.3) | 88/280 (31.4) | 68/197 (34.5) | 410/1277 (32.1) |
| Type of day care at 1 yr of age | ||||
| No care outside home | 791/1978 (40.0) | 133/280 (47.5) | 90/196 (45.9) | 624/1270 (49.1) |
| Small-scale care | 637/1978 (32.2) | 76/280 (27.1) | 61/196 (31.1) | 396/1270 (31.2) |
| Day care centre attendance | 550/1978 (27.8) | 71/280 (25.4) | 45/196 (23.0) | 250/1270 (19.7) |
| Maternal age yrs | 30.5±3.8 (1983) | 30.2±3.9 (285) | 31.1±3.7 (197) | 30.1±4.0 (1292) |
| Maternal BMI before pregnancy kg·m−2 | 22.8±3.3 (1820) | 22.8±3.3 (256) | 22.5±3.4 (184) | 23.0±3.5 (1130) |
| Birth weight g | 3504±546 (1987) | 3525±553 (283) | 3569±601 (197) | 3504±536 (1278) |
| Gestational age weeks | 39.8±1.7 (1990) | 39.8±1.5 (285) | 39.9±1.6 (198) | 39.9±1.6 (1292) |
| Breast feeding duration weeks | 15.3±15.1 (1977) | 15.1±15.0 (285) | 17.3±15.9 (194) | 14.3±14.8 (1290) |
Data are present as n/N (%) or mean±sd (n), unless otherwise stated. FACS: folic acid-containing supplement; BMI: body mass index.