Table 2. Relation between maternal age and preterm birth, low birth weight, and small for gestational age.

Maternal age, years	PTB				LBW				SGA
	<37 weeks		<34 weeks		<2,500 g		<1,500 g
	aOR	95% CI	aOR	95% CI	aOR	95% CI	aOR	95% CI	aOR	95% CI
20–24	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
25–29	1.08	0.91–1.30	1.46	0.94–2.25	1.17	1.03–1.33	1.40	0.81–2.43	1.12	0.95–1.31
30–34	1.39	1.16–1.67	2.23	1.45–3.41	1.34	1.18–1.53	2.30	1.35–3.94	1.24	1.05–1.46
35–39	1.63	1.35–1.98	2.93	1.88–4.56	1.68	1.46–1.93	3.09	1.78–5.38	1.46	1.22–1.74
≥40	2.14	1.66–2.76	4.39	2.59–7.43	2.07	1.71–2.51	4.34	2.23–8.41	1.69	1.32–2.18

aOR, adjusted odds ratio; CI, confidence interval; LBW, low birth weight; PTB, preterm birth; Ref, reference.

aOR was calculated by logistic regression analysis, using maternal education, maternal smoking status, K6 score at the first trimester, and household income.