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. Author manuscript; available in PMC: 2024 May 14.
Published in final edited form as: Birth Defects Res. 2022 Jan 31;114(5-6):184–196. doi: 10.1002/bdr2.1983

FIGURE 2.

FIGURE 2

Study population flow chart and folic acid (FA) exposure group in north and south China, 1993–1996. “PHC” stands for “perinatal health care”; “N” refers to number of pregnancies with known birth outcomes which could be confirmed as either having or not having an NTD. Number in parenthesis is the count of NTD-affected pregnancies. Complete FA exposure group includes women who took 400 μg of folic acid daily between last menstrual period (LMP) and 42 days after LMP with a compliance rate of at least 80%. No FA exposure group includes women who took no folic acid before LMP and during the 60 days after LMP. Incomplete FA exposure group includes all the remaining women, who, for example, started earlier but stopped taking folic acid either before LMP or during the 42-day exposure window, started taking folic acid during the 42-day exposure window, or took folic acid during the 42-day exposure window but with a compliance rate below 80%. Women with incomplete exposure were excluded from further analysis