Table 4 Multivariable logistic regression analysis of prematurity and age for confounding factors (obesity, use of ART, smoking and parity)

Spontaneous

Iatrogenic PTB

Spontaneous

Iatrogenic PTB

Spontaneous

Iatrogenic PTB

< 30 (n 2437)

0.2% (4)

0.1% (2)

0.6% (14)

0.3% (7)

2.4%(58)

1.4% (35)

Ref

Ref

Ref

Ref

Ref

Ref

30–34 (n 9643)

0.1% (13)

0.1% (7)

0.6%(54)

0.4% (35)

2.4%(231)

1.4%(138)

0.55 (0.17–1.78)

1.63 (0.20–13.32)

0.90 (0.46–1.76)

1.54 (0.60–3.98)

1.03 (0.75–1.43)

1.13 (0.74–1.72)

35–39 (n 9887)

0.2% (18)

0.1% (8)

0.6%(57)

0.5%(45)

2.3%(231)

1.6%(163)

0.76 (0.25–2.42)

1.72 (0.21–14.05)

1.01 (0.51–1.95)

1.69 (0.66–4.36)

0.99 (0.71–1.37)

1.23 (0.81–1.88)

40–44 (n 2807)

0.1% (3)

0.1% (2)

0.4% (11)

0.2% (19)

0.7%(72)

2.3%(65)

0.44 (0.08–2.49)

1.41 (0.12–16.31)

0.53 (0.20–1.40)

2.42 (0.86–6.80)

0.95 (0.64–1.43)

1.54 (0.95–2.48)

≥45 (n 280)

0.4% (1)

–

0.4% (1)

1.8% (5)

0.7% (2)

6.1% (17)

2.69 (0.22–33.20)

–

0.56 (0.07–4.72)

3.41 (0.73–15.91)

0.30 (0.07–1.25)

2.62 (1.30–5.27)