Table 1 Characteristics of mother-newborn pairs by newborn sex in the BBC and IOWBC

Total N

180

216

18

30

47

46

Maternal age at delivery, yr*

27.5 (15.3—46.2)

27.6 (16.5—46.8)

0.91

23.0 (20.3—26.6)

23.4 (21.3—27.3)

0.91

23.3 (21.2—29.7)

23.3 (21.2—33.3)

0.93

Type of delivery

0.23

0.78

0.97

Spontaneous vaginal

131 (72.8%)

144 (66.7%)

15 (83.3%)

24 (80.0%)

40 (85.1%)

39 (84.8%)

C-section

49 (27.2%)

72 (33.3%)

3 (16.7%)

6 (20.0%)

7 (14.9%)

7 (15.2%)

Preterm delivery

0.01

0.88

0.57

No

160 (88.9%)

171 (79.2%)

17 (94.4%)

28 (93.3%)

45 (95.7%)

45 (97.8%)

Yes

20 (11.1%)

45 (20.8%)

1 (5.6%)

2 (6.7%)

2 (4.3%)

1 (2.2%)

Maternal smoking during pregnancy

0.87

0.95

0.57

No

159 (88.3%)

193 (89.4%)

11 (61.1%)

18 (60.0%)

29 (61.7%)

31 (67.39%)

Yes

21 (11.7%)

23 (10.6%)

7 (38.9%)

12 (40.0%)

18 (38.3%)

15 (32.6%)

Maternal race/ethnicity

0.57

–

–

Black

115 (63.9%)

145 (67.1%)

–

–

–

–

Non-Black

65 (36.1%)

71 (32.9%)

–

–

–

–

Birth order

0.23

0.65

0.44

First birth

75 (41.7%)

108 (50.0%)

12 (66.7%)

18 (60.0%)

23 (48.9%)

25 (54.4%)

Second birth

52 (28.9%)

50 (23.1%)

4 (22.2%)

8 (26.7%)

11 (36.2%)

13 (28.3%)

Third birth and later

53 (29.4%)

58 (26.9%)

2 (11.1%)

4 (13.3%)

7 (14.9%)

8 (17.4%)