Relationship between hyperemesis gravidarum and small-for-gestational-age in the Japanese population: the Japan Environment and Children’s Study (JECS)

Table 1 Characteristics of all parent-child pairs included in this study (N = 8631)

	No.	(%)	Missing data	No. of non-SGA births	No. of SGA births	% SGA	RR for SGA birth	95 % CI
Mother’s age (years)
19 or less	103	1.3	13	85	5	5.6	0.72	0.30	1.69
20–34^a	5893	75.6	372	5093	428	7.8	(1.0)
35 or more	1801	23.1	83	1610	108	6.3	0.81	0.66	0.99
missing	834		15	774	45
Mother’s education
> 12 years	5227	62.8	320	4558	349	7.1	0.97	0.82	1.14
≤ 12 years^a	3098	37.2	135	2745	218	7.4	(1.0)
missing	306		28	259	19
Parity
0^a	3150	38.4	18	2893	239	7.6	(1.0)
≥ 1	5043	61.6	27	4669	347	6.9	0.91	0.77	1.06
missing	438		438	-	-
Pre-pregnancy body mass index
< 18.5	1363	16.2	69	1153	141	10.9	1.58	1.32	1.90
18.5–24.9^a	6212	73.7	346	5462	404	6.9	(1.0)
≥ 25	856	10.2	34	788	34	4.1	0.60	0.43	0.85
missing	200		34	159	7
Weight gain during pregnancy
< 7 kg	1354	17.7	64	1162	128	9.9	1.28	1.05	1.55
7–12 kg^a	4104	53.6	244	3560	300	7.8	(1.0)
> 12 kg	2198	28.7	102	2011	85	4.1	0.52	0.41	0.66
missing	975		73	829	73
Income
< 4 million yen	3266	41.1	183	2854	229	7.4	1.07	0.90	1.27
4–8 million yen^a	3836	48.3	208	3375	253	7.0	(1.0)
> 8 million yen	843	10.6	53	732	58	7.3	1.05	0.80	1.39
missing	686		39	601	46
Smoked during pregnancy
No^a	7991	94.5	455	7013	523	6.9	(1.0)
Yes	462	5.5	15	401	46	10.3	1.48	1.11	1.97
missing	178		13	148	17
Alcohol intake during pregnancy
No^a	7654	90.2	435	6710	509	7.1	(1.0)
Yes	835	9.8	38	732	65	8.2	1.16	0.90	1.48
missing	142		10	120	12

Data extracted from the Japan Environment and Children’s Study
No. number, SGA small-for-gestational-age, RR risk ratio, CI confidence interval
^aUsed as reference in the calculation of risk ratios

ISSN: 1471-2393