Table 3.

Baseline Maternal Characteristics and Compliance in a Study of Prenatal Micronutrient Supplementation and Spontaneous Preterm Birth, by Timing of Study Enrollment and Supplement Use, Northern China, 2006–2009

Characteristic	Enrollment at ≥12 Gestational Weeks									Enrollment at <12 Gestational Weeks
	FA (n = 2,808)			IFA (n = 2,866)			MMN (n = 2,805)			FA (n = 3,080)			IFA (n = 3,054)			MMN (n = 3,105)
	Mean (SD)	No. of Women	%	Mean (SD)	No. of Women	%	Mean (SD)	No. of Women	%	Mean (SD)	No. of Women	%	Mean (SD)	No. of Women	%	Mean (SD)	No. of Women	%
Gestational week at enrollment	16.1 (2.6)			16.2 (2.5)			16.2 (2.5)			8.3 (2.1)			8.3 (2.1)			8.3 (2.1)
Median level of compliancea			97.0			97.0			97.0			97.0			97.0			97.0
Median no. of supplements consumed		154			154			152			209			208			208
Age at pregnancy, years	23.4 (2.9)			23.4 (2.9)			23.3 (2.8)			23.4 (2.8)			23.4 (2.8)			23.4 (2.8)
Height, cm	160.1 (4.4)			160.1 (4.5)			160.1 (4.5)			160.0 (4.6)			160.3 (4.6)			160.2 (4.5)
Body mass indexb at enrollment	22.6 (2.9)			22.4 (2.8)			22.5 (2.8)			22.0 (2.7)			22.1 (2.9)			22.1 (2.9)
Education
Primary school or lower		526	18.7		494	17.2		479	17.1		563	18.3		570	18.7		588	18.9
Junior high school		2,247	80.0		2,323	81.1		2,279	81.2		2,462	79.9		2,432	79.6		2,475	79.7
High school or higher		35	1.2		49	1.7		47	1.7		55	1.8		52	1.7		42	1.4
Ethnicity
Han		2,779	99.0		2,835	98.9		2,777	99.0		3,034	98.5		3,021	98.9		3,064	98.7
Other		29	1.0		31	1.1		28	1.0		46	1.5		33	1.1		41	1.3
Occupation
Farmer		2,552	90.9		2,618	91.3		2,557	91.2		2,794	90.7		2,775	90.9		2,823	90.9
Other		256	9.1		248	8.7		248	8.8		286	9.3		279	9.1		282	9.1

Abbreviations: FA, folic acid; IFA, iron + folic acid; MMN, multiple micronutrients; SD, standard deviation.

^aCompliance was calculated as the number of supplements consumed divided by the number of days on which supplements were expected to be consumed.

^bWeight (kg)/height (m)².