Table 1. Characteristics of studies included in the meta-analysis.

First author	Year	Country	Ethnicity	Cases			Controls			Study quality score	Genotypes
				N	Age	GAD (weeks)	N	Age	GAD (weeks)
Aggarwal PK	2010	India	Asian	120	25.7	33.2	118	26.3	35.9	9	G894T, T-786C, VNTR 4b/a
Alpoim PN	2014	Brazil	Caucasian	98	25.5	–	103	24	–	7	G894T, T-786C
Bashford MT	2001	USA	Caucasian	87	25	37.4	53	26	39.9	8	VNTR 4b/a
Ben Ali Gannoun M	2015	Tunisia	Africana	345	31.4	35.6	289	30.5	38.2	10	T-786C
Benedetto C	2007	Italy	Caucasian	120	30	34	103	30	39	8	VNTR 4b/a
Chen LK	2007	Taibei	Asian	92	30.2	37.6	256	29.7	38.3	10	VNTR 4b/a
Chen Y	2014	China	Asian	220	29.1	36.4	200	27.2	38.1	8	T-786C, VNTR 4b/a
Coral-Vazquez RM	2013	Mexico	Caucasian	230	25.1	–	352	24.6	–	9	G894T, T-786C
Diaz-Olguin L	2011	Mexico	Caucasian	127	22	–	263	21.6	–	9	G894T, T-786C
Fatini C	2006	Italy	Caucasian	106	29	37	106	28	40.5	9	G894T, T-786C, VNTR 4b/a
Groten T	2014	Germany	Mixeda	158	–	34.2	312	–	39.3	8	G894T, VNTR 4b/a
Hakli T	2003	Finland	Caucasian	132	28.8	34.7	113	28.7	39.8	8	G894T
Hillermann R	2005	South Africa	Africana	50	21	30	50	29	39	7	G894T
Kim YJ	2008	Korea	Asian	223	31	35.7	237	31.1	39.1	9	G894T, T-786C
Kobashi G	2001	Japan	Asian	112	29.6	37	335	29.3	39.1	7	G894T
Landau R	2004	USA	Caucasiana	64	28	–	397	29	–	10	G894T
Leonardo DP	2015	Brazil	Caucasian	77	26.4	35.2	266	24.5	38.7	10	G894T, T-786C, VNTR 4b/a
Lykke JA	2012	Denmark	Caucasian	263	30.2	35.3	1,851	30.3	39.9	14	G894T
Mozgovaia EV	2001	Russia	Caucasian	122	–	–	73	–	–	5	VNTR 4b/a
Nishizawa H	2009	Japan	Asian	33	30.6	–	44	29.5	–	8	G894T
Ozturk E	2011	Turkey	Caucasian	57	29.05	34.54	60	30.2	36.58	9	G894T, VNTR 4b/a
Pappa KI	2011	Greece	Caucasian	51	26	–	116	27	–	7	G894T
Perlik M	2012	Poland	Caucasian	41	29.46	36.88	150	28.3	39.06	5	G894T, T-786C
Rahimi Z	2013	Iran	Caucasian	179	29.2	–	96	27.5	–	9	VNTR 4b/a
Rahimi Z	2013	Iran	Caucasian	198	29.1	–	101	27.4	–	9	G894T
Sakar MN	2014	Turkey	Caucasian	56	28.39	35.41	80	28.2	39.11	7	G894T
Salimi S	2012	Iran	Caucasian	123	28	36.6	142	26.5	37.9	9	VNTR 4b/a
Sandrim VC	2010	Brazil	Mixeda	98	26.4	36	107	24.8	40.9	9	G894T, T-786C, VNTR 4b/a
Sandrim VC	2008	Brazil	Mixeda	113	26.4	35.9	110	26	40.7	9	G894T, T-786C, VNTR 4b/a
Seremak-Mrozikiewicz A	2008	Poland	Caucasian	150	28.3	35.4	226	27.9	39.4	6	T-786C
Seremak-Mrozikiewicz A	2011	Poland	Caucasian	218	28.6	35.7	400	27.3	39.2	9	T-786C
Serrano NC	2004	Colombia	Mixeda	322	19.2	36.4	522	18.9	39.1	10	G894T, VNTR 4b/a
Singh A	2010	India	Asian	50	–	–	50	–	–	7	G894T
Tempfer CB	2001	USA	Caucasiana	66	26	36.7	44	25	39.9	7	VNTR 4b/a
Turan F	2010	Turkey	Caucasian	55	32	–	54	29.6	–	7	G894T
Yaghmaei M	2011	Iran	Caucasian	147	28.1	36.6	137	26.3	38.2	8	G894T
Yoshimura T	2003	Japan	Asian	112	24.5	–	119	24.6	–	8	G894T
Yoshimura T	2000	Japan	Asian	152	30	36	170	30.6	39.4	9	G894T
Yu CK	2006	UK	Mixeda	89	–	–	349	–	–	11	G894T
Zdoukopoulos N	2011	Greece	Caucasian	102	30.64	35.41	176	29.6	38.58	8	G894T, T-786C, VNTR 4b/a
Zhang ZH	2007	China	Asian	53	29.2	–	49	28.7	–	5	G894T

GAD: gestational age at delivery; VNTR: variable number of tandem repeats;

^aOther refers to mixed ethnicity with Caucasians and Africans.