Table 1

Baseline characteristics of the study population (n=4680)

Characteristics
Maternal characteristics
 Age at intake (year)31.08 (4.56)
 Weight before pregnancy (kg)64 (34–145)
 Height measured at intake (cm)168.80 (7.12)
 Educational level
  Low653 (14.0%)
  Mid–low1333 (28.5%)
  Mid–high1129 (24.1%)
  High1419 (30.3%)
  Missing146 (3.1%)
 Ethnicity
  The Netherlands2993 (64.0%)
  Surinam and Dutch Antilles380 (8.1%)
  Morocco and Turkey328 (7.0%)
  Other885 (18.9%)
  Missing94 (2.0%)
 Parity
  Nulliparous2992 (63.9%)
  Multiparous1565 (33.4%)
  Missing123 (2.6%)
 Smoking
  Yes, during pregnancy546 (11.7%)
  Yes, until pregnancy was known355 (7.6%)
  No3031 (64.8%)
  Missing748 (16.0%)
 Alcohol
  Yes, during pregnancy1846 (39.4%)
  Yes, until pregnancy was known587 (12.5%)
  No1524 (32.6%)
  Missing723 (15.4%)
 Folic acid use
  No580 (12.4%)
  Yes, postconception start1163 (24.9%)
  Yes, preconception start1735 (37.1%)
  Missing1202 (25.7%)
 Maternal occupational characteristics
  Long periods of standing, occasionally920 (19.7%)
  Long periods of standing, often883 (18.9%)
  Long periods of walking, occasionally1467 (31.3%)
  Long periods of walking, often665 (14.2%)
  Lifting >25 kg, occasionally217 (4.6%)
  Lifting >25 kg, often70 (1.5%)
  Night shifts, occasionally137 (2.9%)
  Night shifts, often60 (1.3%)
  Work hours 1–24 h/week1193 (25.5%)
  Work hours 25–39 h/week2222 (47.5%)
  Work hours >40 h/week1087 (23.2%)
Growth outcomes
 Second trimester ultrasonography4197 (89.7%)
 Third trimester ultrasonography4294 (91.8%)
Birth outcomes
 Gestational age at birth (week)40.14 (22.71–43.43)
 Birth weight (g)3449.81 (549.28)
 Men2365 (50.5%)
 Head circumference at birth (mm)33.89 (1.65)
 Length at birth (mm)50.33 (2.38)
 Low birth weight (<2500 g)
  Yes203 (4.3%)
  No4674 (99.9%)
  Missing6 (0.1%)
 Small for gestational age (<−1.7 SD)
  Yes201 (4.3%)
  No4463 (95.7%)
  Missing16 (0.3%)
 Preterm delivery (<37 weeks of gestation)
  Yes231 (4.9%)
  No4449 (95.1%)
  • Values are means (SD) for normal distributed continuous variables or medians (minimum–maximum) for skewed distributed continuous variables and absolute numbers (percentages) for categorical variables.