The effect of pre-pregnancy hair dye exposure on infant birth weight: a nested case-control study

Table 4 Combined effects of underweight / irregular menstruation and hair dye use pre-pregnancy on LBW study

	Unadjusted			Adjusted
	OR (95% CI)	P	P _trend	OR (95% CI)	P	P _trend
Type-1 model ^a
Neither of them	1.00 (Reference)			1.00 (Reference)
Only BMI < 18.5 kg/m² or hair dye use pre-pregnancy	2.52 (1.33, 4.78)	0.005	0.012	2.53 (1.30, 4.93)	0.006	0.015
Both BMI < 18.5 kg/m² and hair dye use pre-pregnancy	2.96 (1.39, 6.33)	0.005		3.07 (1.38, 6.83)	0.006
Type-2 model ^b
Neither of them	1.00 (Reference)			1.00 (Reference)
Only irregular menstruation or hair dye use pre-pregnancy	2.16 (1.20, 3.89)	0.010	0.030	2.07 (1.14, 3.76)	0.018	0.050
Both irregular menstruation and hair dye use pre-pregnancy	4.58 (2.02, 10.40)	< 0.001		4.53 (1.94, 10.59)	< 0.001

Abbreviations: LBW low birth weight, OR odds ratio, 95% CI 95% confidence interval, BMI body mass index is measured and defined as weight (kg) / height (m)²
^aLogistic regression model is adjusted for maternal age, maternal education level, parity and menstruation cycle
^bLogistic regression model is adjusted for maternal age, maternal education level, parity and pre-pregnant body mass index

ISSN: 1471-2393