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Table 2 Characteristics of the women in UK Biobank, ALSPAC, BiB and MoBa included in Mendelian randomization

From: Investigating causal relations between sleep duration and risks of adverse pregnancy and perinatal outcomes: linear and nonlinear Mendelian randomization analyses

Variable a UK Biobank (N=176,897) ALSPAC (N=6826) BiB (N=2940) MoBa (N=14,584)
  Mean (standard deviation)
Maternal age (years) 25.5 (4.6) b 28.7(4.7) 26.8 (6.0) 30.0 (4.5)
Maternal height (cm) 162.5 (6.2) 164.3 (6.7) 164.4 (6.1) 168.4 (5.7)
Maternal body mass index (kg/m2) 27.0 (5.1) 22.9 (3.7) 26.7 (6.0) 24.0 (4.2)
Parity 2.2 (1.0) 0.8 (0.9) 0.8 (1.1) 0.7 (0.8)
Gestational age (weeks) 38.9 (3.8) c 39.6 (1.7) 39.7 (1.9) 39.6 (1.7)
Offspring birthweight (grams) 3186.7 (547.6) 3441.5 (523.0) 3357.9 (571.2) 3640.8 (513.4)
  N (%)
Maternal education
 O levels/GCSEs or equivalent and below 81,113 (46.4) 4043 (59.5) 1400 (47.6) 252 (1.7)
 A levels/AS levels or equivalent 40,817 (23.3) 1719 (25.3) 485 (16.5) 4378 (30.0)
 College or university degree 53,062 (30.3) 1035 (15.2) 551 (18.7) 9100 (62.4)
Maternal ever smoking 74,308 (42.2) 1450 (21.6) d 911 (31.0) d 1106 (7.6) d
Maternal ever drinking 162,436 (92.0) 4580 (70.2) d 1793 (61.0) d 3644 (25.0) d
Offspring sex, male Not available 3430 (50.2) 1504 (51.2) 7456 (51.1)
Number with fetal genotype data 0 4625 (67.8) 1855 (63.1) 12,183 (83.5)
  N cases / N controls (Proportion, %)
Stillbirth 4907/107,791 (4.4) 48/4546 (1.0) 31/2588 (1.2) 51/9998 (0.5)
Miscarriage 42,717/107,791 (28.4) 1378/4546 (23.3) 14/2588 (0.5) 2677/9998 (21.1)
Gestational diabetes mellitus 726/170,308 (0.4) 34/6283 (0.5) 136/2657 (4.9) 113/14,375 (0.8)
Hypertensive disorders of pregnancy 2128/174,769 (1.2) 1099/5698 (16.2) 347/2159 (13.8) 1892/12,652 (13.0)
Perinatal depression 5168/20,860 (19.9) 423/5896 (6.2) 312/2245 (12.2) 579/13,865 (4.0)
Preterm birth 551/4811 (10.3) c 285/4931 (5.5) 172/2706 (6.0) 495/12,846 (3.7)
Low offspring birthweight 13,429/149,084 (8.3) 337/6376 (5.0) 167/2725 (5.8) 245/13,690 (1.8)
High offspring birthweight 2716/149,084 (1.8) 113/6376 (1.7) 42/2725 (1.5) 621/13,690 (4.3)
  1. aIn UKB, these variables were measured at the recruitment that is typically many years after pregnancy
  2. bWe report maternal ages at giving their first live birth. UK Biobank women were recruited with an average age of 56.9 (standard deviation 7.8) years
  3. cGestational age was available only in a small subset of UK Biobank women (N=7280)
  4. dThese were maternal ever smoking/drinking in pregnancy
  5. ALSPAC Avon Longitudinal Study of Parents and Children, BiB Born in Bradford, MoBa Norwegian Mother and Child Cohort Study