Table 4 Multivariable analysis of perinatal risk factors for infant mortality at different periods by Cox regression model

GA 25-27 (week)

2.99 (1.10, 8.16)^*

0.59 (0.09, 3.81)

33.31 (12.23, 90.72)^***

28-31

3.62 (1.53, 8.58)^**

1.02 (0.29, 3.66)

2.31 (0.72, 7.41)

32-36

2.15 (1.08, 4.27)^*

0.34 (0.12, 1.02)

0.39 (0.13, 1.19)

37-38

1.62 (1.00, 2.65)

1.34 (0.64, 2.81)

0.72 (0.39, 1.32)

39-41

1.00 (Reference)

1.00 (Reference)

1.00 (Reference)

>  42

–

9.77 (2.24, 42.69)^**

1.52 (0.21, 11.10)

BW < 1000 (g)

27.15 (10.36, 71.16)^***

86.88 (12.37, 610.07)^***

NI

1000-1499

4.26 (1.85, 9.79)^**

9.08 (2.48, 33.24)^**

NI

1500-2499

2.02 (1.08, 3.78)^*

4.76 (2.02, 11.24)^***

NI

2500-3999

1.00 (Reference)

1.00 (Reference)

NI

>  4000

0.19 (0.05, 0.79)^*

1.17 (0.40, 3.41)

NI

Maternal age < 20 (y)

NI

2.54 (0.90, 7.21)

NI

20-34

NI

1.00 (Reference)

NI

>  35

NI

2.32 (1.18, 4.58)^*

NI

Rural residency

1.41 (0.96, 2.09)

NI

NI

Education > 9 y

0.66 (0.45, 0.96)^*

NI

0.59 (0.36, 0.97)^*

PROM

NI

1.89 (1.02, 3.51)^*

NI

Umbilical cord

1.82 (1.07, 3.08)^*

NI

NI

Antenatal steroids

0.42 (0.26, 0.68)^***

NI

NI

AF contamination

2.03 (1.36, 3.01)^***

2.00 (1.07, 3.73)^*

NI

Multiple births

NI

NI

4.31 (2.02, 9.23)^***

Apgar 5-min < 7

17.89 (11.40, 28.07)^***

1.90 (0.92, 3.92)

NI

Congenital anomalies

3.18 (2.13, 4.75)^***

12.07 (6.85, 21.27)^***

6.90 (3.61, 13.19)^***

Hospitalization

3.03 (1.92, 4.80)^***

31.41 (10.64, 92.67)^***

3.30 (1.91, 5.71)^***