Impact of preconception enrollment on birth enrollment and timing of exposure assessment in the initial vanguard cohort of the U.S. National Children’s Study

Table 3 Time interval from preconception study visit to conception, by eligibility status at the time of consent (n = 161)^a

Time interval relative to conception	High non-tryer	High tryer	All preconception
	%	%	%
More than 90 days before conception	51.9	32.7	39.1
31 to 90 days before conception	9.3	16.8	14.3
30 days before or after conception	13.0	21.5	18.6
More than 30 days after conception	11.1	14.0	13.0
No preconception visit recorded^b	14.8	15.0	14.9
Total	100	100	100

^aThe table excludes four women with an unknown estimated date of conception
^b11 % of all preconception women had a conception date after August 2010, a time period for which data on study visits was not available

ISSN: 1471-2288