Table 3. Associations between obstetric outcomes and external radiation dose (imputation of missing doses).

		Congenital anomaly						Low birth weight
		Crude			Multivariate adjusted			Crude			Multivariate adjusted
	Ref.	OR	(95% CI)	P *	OR	(95% CI)	P **	OR	(95% CI)	P *	OR	(95% CI)	P **
External radiation dose
1 to <2 mSv	<1 mSv	0.81	(0.56–1.17)	0.253				0.91	(0.71–1.17)	0.448	0.91	(0.71–1.18)	0.472
≥2 mSv	<1 mSv	—	—					1.26	(0.56–2.83)	0.581	1.21	(0.53–2.79)	0.649
Maternal age	1SD	0.95	(0.82–1.10)	0.456				1.04	(0.94–1.14)	0.458
Child’s sex	Female	1.20	(0.90–1.61)	0.221				0.65	(0.53–0.79)	<0.001	0.65	(0.53–0.79)	<0.001
Gestational days at delivery	1SD	0.79	(0.71–0.88)	<0.001				0.26	(0.23–0.29)	<0.001
Primiparous	Multiparous	0.89	(0.63–1.26)	0.511				1.21	(0.98–1.50)	0.078
LBW	≥2,500 g	2.78	(1.88–4.09)	<0.001				—	—
SGA	≥−10%	1.67	(1.07–2.59)	0.023				21.6	(17.2–27.0)	<0.001
Preterm birth	≥37 weeks	3.83	(2.40–6.11)	<0.001				30.5	(22.6–41.2)	<0.001
Placenta previa	No	—	—					1.80	(0.95–3.40)	0.070
Forced to change health check-up facility	No	1.36	(1.02–1.83)	0.038				1.02	(0.84–1.25)	0.830
Trimester of pregnancy at earthquake
Second (14–28 weeks)	First	0.78	(0.46–1.30)	0.335				1.12	(0.88–1.41)	0.363
Third (≥28 weeks)	First	0.57	(0.31–1.05)	0.069				1.05	(0.81–1.37)	0.709
Infertility treatment	No	1.31	(0.72–2.37)	0.376				1.54	(1.04–2.27)	0.031	1.49	(1.01–2.21)	0.046
Hypertensive disorders of pregnancy	No	0.84	(0.34–2.05)	0.695				4.18	(2.97–5.89)	<0.001	4.14	(2.93–5.84)	<0.001
Mental disorders before birth	No	1.66	(1.01–2.73)	0.045				0.89	(0.58–1.36)	0.592
Evacuation area	No	0.99	(0.62–1.58)	0.959				0.91	(0.66–1.26)	0.573
		SGA						Preterm birth
		Crude			Multivariate adjusted			Crude			Multivariate adjusted
	Ref.	OR	(95% CI)	P *	OR	(95% CI)	P **	OR	(95% CI)	P *	OR	(95% CI)	P **
External radiation dose
1 to <2 mSv	<1 mSv	1.12	(0.91–1.40)	0.286	1.14	(0.92–1.42)	0.229	0.92	(0.65–1.30)	0.638	0.91	(0.65–1.29)	0.602
≥2 mSv	<1 mSv	0.84	(0.30–2.39)	0.744	0.84	(0.30–2.37)	0.735	1.08	(0.24–4.84)	0.919	1.05	(0.22–4.87)	0.955
Maternal age	1SD	0.93	(0.85–1.02)	0.105				1.17	(1.02–1.34)	0.025	1.13	(0.98–1.29)	0.084
Child’s sex	Female	0.87	(0.73–1.04)	0.134				1.28	(0.97–1.69)	0.081
Gestational days at delivery	1SD	1.07	(0.98–1.18)	0.150				—	—
Primiparous	Multiparous	0.72	(0.58–0.90)	0.004	0.69	(0.56–0.87)	0.001	1.05	(0.77–1.43)	0.753
LBW	≥2,500 g	21.6	(17.2–27.0)	<0.001				30.5	(22.6–41.2)	<0.001
SGA	≥−10%	—	—					1.32	(0.85–2.05)	0.222
Preterm birth	≥37 weeks	1.32	(0.85–2.05)	0.222
Placenta previa	No	0.50	(0.18–1.36)	0.174				5.01	(2.73–9.17)	<0.001	4.81	(2.60–8.89)	<0.001
Forced to change health check-up facility	No	0.94	(0.77–1.13)	0.496				0.97	(0.72–1.30)	0.823
Trimester of pregnancy at earthquake
Second (14–28 weeks)	First	0.93	(0.75–1.15)	0.490				1.08	(0.78–1.48)	0.650
Third (≥28 weeks)	First	1.09	(0.87–1.37)	0.465				0.77	(0.52–1.12)	0.173
Infertility treatment	No	1.12	(0.74–1.68)	0.597				1.33	(0.75–2.36)	0.334
Hypertensive disorders of pregnancy	No	2.88	(2.01–4.12)	<0.001	3.01	(2.10–4.32)	<0.001	4.63	(2.99–7.17)	<0.001	4.50	(2.89–7.00)	<0.001
Mental disorders before birth	No	0.73	(0.48–1.12)	0.147				0.92	(0.51–1.67)	0.791
Evacuation area	No	0.89	(0.65–1.20)	0.438				0.79	(0.48–1.28)	0.332

CI, confidence interval; LBW, low birth weight; OR, odds ratio; SGA, small for gestational age.

^*Univariate logistic regression analysis by forced entry method.

^**Factors significant in univariate analysis were entered into multivariate analysis using binominal logistic regression.