We calculated the days between dates of each vaccination and dates of estimated conception; we used dates of first vaccination dose, most recent vaccination dose before the estimated conception date, and vaccination dose nearest to (whether before or after) the estimated conception dates as three different origins of time scales.
We included women with live births only because we needed to obtain an estimated conception date for each woman.
For the current study, only children whose estimated conception month was June 1989 or later were included because nurses' addresses before this month were unknown.
We calculated the time between conception and vaccination as the number of days between the estimated conception of a pregnancy and the nearest vaccination that was administered before the end of the pregnancy.
§Rates are percentages of all pregnancies with miscarriage in specified interval of gestational age. Figure 2 shows the counts of miscarriages and pregnancies and the rates by arm according to the time between nearest vaccination and date of estimated conception.
Birth date, gestational age at delivery (used to generate estimated conception date) and the geographic coordinates for maternal residences for all births in New York City 2008 2010 were obtained from the Bureau of Vital Statistics, New York City Department of Health and Mental Hygiene.
From this estimated conception date, we built several time periods for analysis of psychotropic drug exposures: 1) weeks 1 to 13 of gestation (first trimester); 2) Weeks 14 to 26 of gestation (second trimester), 3) week 27 of gestation to delivery (third trimester), 4) 6 months prior to conception (preconception) and, 5) six months postpartum (postpartum).
Cluster output (Fig. 1) includes a 5 year timeline and details of the cluster with number of cases, start and end date of estimated conception, "expected" number of cases during the time period of the cluster (i.e. the average no. cases per day multiplied by the number of days), lambda (the scan statistics), and probability.
In practice, an accurate estimate of conception date may seldom be available outside the setting of in vitro fertilization.
We did have an excellent estimate of conception, given the longitudinal capture of menstruation, sexual intercourse, and hCG-confirmed pregnancy.
