Table 1 Maternal, pregnancy, delivery and newborn characteristics of participants and eligible non participants, stratified by singleton/multiple status

 Maternal education (years), mean (SD)

11.0 (4.3)

9.4 (4.0)

< 0.001

11.4 (4.5)

9.7 (4.4)

 Maternal age (years), mean (SD)

29.7 (5.3) ^a

27.7 (5.9)

< 0.001

30.5 (4.1) ^a

29.6 (5.4)

 Pre-pregnancy BMI (kg/m²), mean (SD)

23.9 (4.2)

23.8 (4.5)

0.435

23.7 (4.0)

24.8 (3.7)

  Married/Living with a partner

5126 (94.9)

2638 (91.1)

99 (97.1)

41 (100.0)

  Single/Widowed/Divorced/Separate

273 (5.1)

259 (8.9)

< 0.001

3 (2.9)

0 (0.0)

  Multiparae

2219 (40.9)

1334 (45.7)

34 (33.3)

13 (31.7)

  Primiparae

3212 (59.1)

1586 (54.3)

< 0.001

68 (66.7)

28 (68.3)

 Fertility treatment, n (%)

110 (2.1) ^a

31 (1.1)

0.001

23 (23.0) ^a

5 (12.2)

 Gestational diabetes, n (%)

339 (6.3)

175 (6.1)

0.662

5 (4.9)

3 (7.5)

 Hypertension, n (%)

131 (2.4)

64 (2.2)

0.531

4 (3.9)

0 (0.0)

 Pre-eclampsia / Eclampsia, n (%)

57 (1.1) ^a

42 (1.5)

0.116

5 (4.9) ^a

3 (7.5)

 Tobacco smoke during 3rd trimester, n (%)

629 (11.9)

542 (19.2)

< 0.001

6 (5.9)

5 (13.2)

 Weight gain (kg)

12.8 (5.3) ^a

12.7 (5.7)

0.520

14.8 (6.5) ^a

12.8 (6.8)

 Gestational age (weeks), mean (SD)

38.7 (1.7) ^a

38.6 (1.9)

0.077

34.7 (3.0) ^a

34.1 (3.1)

  Vaginal

3362 (63.1) ^a

1933 (67.5)

29 (29.9) ^a

12 (29.3)

  Caesarean

1967 (36.9) ^a

931 (32.5)

< 0.001

68 (70.1) ^a

29 (70.7)

 Triplets, n (%)

–

–

n.a.

12 (5.8)

6 (7.1)

 Monozygotia, n (%)

–

–

n.a.

31 (31.3)

3 (11.1)

  Male

2798 (51.5)

1468 (50.3)

105 (50.5) ^c

38 (45.2) ^c

  Female

2633 (48.5)

1452 (49.7)

0.278

103 (49.5) ^c

46 (57.8) ^c

 Birthweight (g), mean (SD)

3193 (488) ^a

3173 (509)

0.090

2152 ^ac

2032 ^c

  Z-score, mean (SD)

−0.31 (0.87) ^a

-0.31 (1.1)

0.897

− 0.83 ^ac

− 0.83 ^c

  Small for gestational age, n (%)

675 (12.5) ^a

387 (13.4)

60 (29.3) ^ac

23 (27.4) ^c

  Normal for gestational age, n (%)

4542 (84.0) ^a

2372 (82.2)

143 (69.8) ^ac

60 (71.4) ^c

  Large for gestational age, n (%)

189 (3.5) ^a

126 (4.4)

0.056

2 (1.0) ^ac

1 (1.2) ^c

 Phototherapy treatment, n (%)

659 (13.3) ^a

349 (13.3)

0.979

64 (39.5) ^ac

41 (57.7) ^c

 NICU admission, n (%)

314 (6.4) ^a

209 (8.0)

0.011

91 (52.6) ^ac

40 (57.1) ^c

 APGAR 5′ < 7, n (%)

29 (0.6) ^a

15 (0.5)

0.906

7 (3.8) ^{a c}

4 (4.9) ^c