Table 2. Prevalence of anemia among pregnant women in different trimesters — 6 provinces in China, 2014–2018.

Variables	First trimester (<13 weeks)				Second trimester (<28 weeks)				Third trimester ( ≥ 36 weeks)				Total
	Number	Prevalence of anemia (%)	χ2		Number	Prevalence of anemia (%)	χ2		Number	Prevalence of anemia (%)	χ2		Number	Prevalence of anemia (%)	χ2
Note: The six provinces (with the selected districts) are: Hebei (Xinhua and Zhengding), Liaoning (Lishan, Tiedong, and Taian), Hunan (Yueyanglou and Yueyang), Fujian(Haicang and Jimei), Sichuan (Gongjing and Rong County) and Yunnan (Tonghai and Huaning). Taian stopped surveillance in 2016, and Tiedong County became the participant since then. Rao-Scott chi-square tests were conducted to test for differences in prevalence for unordered categorical variables. Based on the economic development level and administrative divisions, Hebei and Liaoning provinces represented the northeast region, Hunan and Fujian provinces the central region, and Sichuan and Yunnan provinces the southwest region. In addition, pregnant woman were classified as natives or outsiders of the counties on the basis of the census registration. Gestational week was based on the number of days between the first day of an expectant mother’s LMP and the date of antenatal examination. The first, second, and third trimester were defined as a gestational age less than 13 weeks, 13–27 weeks, and 28–42 weeks, respectively. * p<0.001. † p<0.05.
Regions			242.45*				128.04*				916.09*				2614.20*
Northeast	14,581	4.62			36,875	43.05			24,881	80.85			76,337	48.03
Central	37,018	8.56			22,646	43.12			24,372	69.60			84,036	35.58
Southwest	17,478	8.29			12,918	48.53			15,984	78.33			46,380	43.64
Age			34.23*				32.20*				179.53*				89.04*
<25	15,740	8.41			14,679	46.11			15,258	78.39			45,688	43.90
25–35	47,196	7.24			50,312	43.51			43,475	76.16			140,983	41.44
>35	5,875	8.75			7,155	43.48			6,207	69.79			19,252	41.38
Education			143.29*				120.16*				72.80*				354.32*
Junior high or lower	25,983	8.94			25,151	46.33			26,946	77.72			78,080	44.72
Senior high school	18,333	7.94			16,565	45.10			16,417	75.86			51,315	41.66
University or above	23,139	6.08			30,098	41.83			21,252	74.41			74,489	40.02
Parity			48.23*				2.33				3.49				306.23*
0	34,580	6.93			36,893	43.88			30,128	76.24			101,601	40.90
≥1	28,712	8.40			34,345	44.45			34,264	75.61			97,321	44.78
Number of ANC examinations			50.59*				1902.86*				2327.02*				1820.44*
<5	4,311	4.87			9,252	23.02			6,099	50.93			19,662	27.70
≥5	64,766	7.85			63,187	47.13			59,138	78.62			187,091	43.48
Number of Hb tests			85.19*				4731.27*				7043.13*				5764.56*
<3	13,552	5.77			20,676	23.97			15,388	50.79			49,616	27.32
≥3	55,525	8.12			51,763	52.07			49,849	83.83			157,137	46.61
Delivery week			6.12†				29.25*				114.35*				215.88*
<37 weeks	2,822	6.45			69,158	44.27			63,342	76.34			198,755	42.30
≥37 weeks	66,255	7.71			3,281	39.47			1,895	65.70			7,998	34.03