Table 1 Baseline characteristics of study participants

Age, years

30.2 ± 4.4^a

30.4 ± 4.7

30.3 ± 4.5

Height, cm

167.4 ± 6.0

167.2 ± 6.0

167.3 ± 6.0

Pregravid weight, kg

68.4 ± 13.1

68.0 ± 13.7

68.2 ± 13.4

Pregravid BMI, kg/m²

24.4 ± 4.4

24.3 ± 4.6

24.4 ± 4.5

Pregravid BMI category, n (%)

 BMI 18.5–24.9 kg/m²

732/1139 (64.3%)

735/1122 (65.5%)

1467/2261 (64.9%)

 BMI 25.0–29.9 kg/m²

271/1139 (23.8%)

249/1122 (22.2%)

520/2261 (23.0%)

 BMI 30.0–40.0 kg/m²

136/1139 (11.9%)

138/1122 (12.3%)

274/2261 (12.1%)

Gestational age at entry, weeks

8.1 ± 2.1

8.4 ± 2.2

8.3 ± 2.2

Nulliparous, n (%)

706/1139 (62.0%)

593/1119 (53.0%)

1299/2258 (57.5%)

Current smoker, n (%)

60/1061 (5.7%)

64/1044 (6.1%)

124/2105 (5.9%)

Number of cigarettes per day (smokers)

4.6 ± 3.1

6.2 ± 4.4

5.4 ± 3.9

Previous caesarean section

105/1027 (10.2%)

117/1013 (11.5%)

222/2040 (10.9%)

Previous preterm birth

26/1027 (2.5%)

30/1013 (3.0%)

56/2040 (2.7%)

Country of birth, n (%)

 Germany

1001/1138 (88.0%)

1001/1118 (89.5%)

2002/2256 (88.7%)

 Other

137/1138 (12.0%)

117/1118 (10.5%)

254/2256 (11.3%)

 Living with a partner

1093/1134 (96.4%)

1065/1118 (95.3%)

2158/2252 (95.8%)

Educational level

 None

2/1138 (0.2%)

4/1115 (0.4%)

6/2253 (0.3%)

 General secondary school

172/1138 (15.1%)

182/1115 (16.3%)

354/2253 (15.7%)

 Intermediate secondary school

486/1138 (42.7%)

466/1115 (41.8%)

952/2253 (42.3%)

 High school/Grammar school

478/1138 (42.0%)

463/1115 (41.5%)

941/2253 (41.8%)

 University degree

297/1132 (26.2%)

296/1105 (26.8%)

593/2237 (26.5%)