Table 1

Maternal and Infant Characteristics Among Singletons and Twins Born at 24 Weeks of Gestation or Later, United States, 1995-96 and 2004-05

Maternal characteristics*

Singletons

Twins


1995-96

2004-05

Odds ratio (95%CI)

1995-96

2004-05

Odds ratio (95%CI)


No. of women

6,359,866

6,122,022

82,639

101,572

Age (years) <20

13.3

10.6

0.77 (0.77-0.77)

7.24

5.14

0.70 (0.68-0.71)

20-24

24.8

25.8

1.06 (1.05-1.06)

19.6

18.0

0.90 (0.89-0.92)

25-29

27.5

27.4

0.99 (0.99-1.00)

27.7

26.1

0.92 (0.91-0.92)

30-34

23.0

22.7

0.98 (0.98-0.99)

28.9

29.1

1.01 (1.00-1.03)

35-39

9.72

11.0

1.15 (1.15-1.15)

14.2

16.9

1.23 (1.20-1.25)

40+

1.73

2.45

1.43 (1.42-1.44)

2.44

4.73

1.98 (1.91-2.06)

Race: Non-Hispanic white

66.2

58.9

0.73 (0.73-0.73)

69.2

65.5

0.84 (0.83-0.85)

African American

16.5

15.4

0.93 (0.92-0.93)

18.1

16.8

0.91 (0.90-0.93)

Hispanic

13.3

20.2

1.64 (1.64-1.65)

9.81

13.4

1.42 (1.39-1.45)

Other

4.04

5.56

1.40 (1.39-1.41)

2.89

4.31

1.51 (1.46-1.57)

Maternal education <12 years

20.8

20.6

0.98 (0.98-0.98)

15.3

13.6

0.84 (0.83-0.86)

Smoking during pregnancy

13.8

11.1

0.78 (0.78-0.78)

12.4

9.00

0.70 (0.68-0.71)

Unmarried

32.4

36.8

1.22 (1.21-1.22)

27.9

28.6

1.03 (1.02-1.05)

No prior live births

42.3

40.4

0.93 (0.92-0.93)

21.9

22.4

1.02 (1.01-1.04)

Infant sex (male)

51.2

51.2

1.00 (1.00-1.00)

49.9

50.2

1.01 (1.00-1.02)

Congenital anomalies (yes)

1.59

1.17

0.74 (0.73-0.74)

2.44

1.66

0.69 (0.66-0.72)

Gestational age-specific

Stillbirths: 24-27 wks

13.4

11.6

0.85 (0.81-0.90)

6.16

4.66

0.74 (0.64-0.87)

28-31

7.78

6.91

0.88 (0.84-0.92)

3.10

1.89

0.60 (0.51-0.70)

32-33

4.19

3.51

0.83 (0.78-0.88)

1.26

0.59

0.47 (0.37-0.59)

34-36

1.21

0.95

0.78 (0.74-0.81)

0.51

0.28

0.54 (0.45-0.63)

> = 37

0.13

0.11

0.81 (0.79-0.84)

0.24

0.15

0.61 (0.49-0.76)

All

0.34

0.30

0.88 (0.86-0.89)

0.80

0.51

0.64 (0.59-0.69)

Neonatal deaths: 24-27 wks

18.5

16.4

0.87 (0.83-0.91)

23.0

18.5

0.76 (0.69-0.83)

28-31

4.11

3.69

0.89 (0.84-0.95)

3.03

2.54

0.83 (0.72-0.97)

32-33

1.89

1.63

0.88 (0.80-0.96)

0.71

0.62

0.86 (0.66-1.12)

34-36

0.61

0.50

0.81 (0.77-0.87)

0.39

0.25

0.65 (0.53-0.78)

> = 37

0.10

0.08

0.76 (0.73-0.79)

0.20

0.11

0.55 (0.43-0.72)

All

0.24

0.21

0.87 (0.85-0.89)

1.17

1.95

0.80 (0.75-0.86)


*Women with missing information excluded: 5-8% for smoking status and 1-5% for congenital anomalies. All proportions based on live births except for stillbirth rates which were based on total births.

All differences in maternal/infant characteristics between 1995-96 and 2004-05 were statistically significant (P < 0.05) except for the differences in infant sex and the proportion of twin births at 32-33 weeks of gestation.

Lisonkova et al. BMC Pregnancy and Childbirth 2011 11:39   doi:10.1186/1471-2393-11-39

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