Women aged 18–55 years with an estimated LMP date (i.e., pregnancy start date) and pregnancy end date between 01 January 2016 and 31 December 2017 were identified. This time period was chosen because this validation study was conducted as background for surveillance that began in 2018. The population was limited to women who had continuous medical and pharmacy benefit coverage for a minimum of 6 months prior to their estimated LMP date (i.e., the baseline period) through to the end of pregnancy. Within this study population, the infant study population was identified among pregnancies for which the mother and infant data could be linked.
The ORD contains data from health plans that contract for “administrative services only”; access to medical records was not allowed for patients enrolled in these health plans. As this study required medical record review, women and infants who were enrolled in “administrative services only” plans were excluded from the study population, and the study outcomes were identified among those remaining (Fig. 1a, b).

a Cohort creation flow diagram for women/pregnancies. DAPI Dynamic Assessment of Pregnancies and Infants, LMP last menstrual period. aHave continuous medical and pharmacy benefit coverage for a minimum of 6 months (182 days) prior to and including the estimated LMP through the end of pregnancy. bEarliest LMP occurring on or after 01JAN2016; end of pregnancy ending by 31DEC2017. cThis step determines women for whom Optum can seek medical charts for the pregnancy and outcome, assessed at the pregnancy episode level. Pregnancies among women enrolled in administrative services only plans were excluded because access to medical records was not allowed for patients in these plans. The final study population consisted only of women with pregnancies for whom Optum could seek medical charts. b Cohort creation flow diagram for infants. aSee Figure 1a for details of the study population creation. bThis is “multi-gestation” pregnancies that have livebirth(s) and stillbirth(s) (e.g. twins, one liveborn and one stillborn; quadruplets, some liveborn). cIncludes stillbirths, ectopic, molar, and abortions (“spontaneous,” “elective,” and “other” per DAPI definitions). dLinked pregnancies are pregnancies for which the mother and infant data could be linked. Forty-one linked infants were from pregnancies ending in a non-livebirth, possibly representing misclassification of how these pregnancies ended. eThis step determines infants for whom Optum can seek medical charts. Infants enrolled in administrative services only plans were excluded because access to medical records was not allowed for patients in these plans. The final study population consisted only of infants for whom Optum could seek medical charts

Each pregnancy was followed from the day after the estimated LMP date through to the first of the following: 60 days after the date of end of pregnancy, disenrollment from the health plan, or end of the study period. Infants who were linked to their mothers were followed from the estimated date of delivery through to the first of the following: disenrollment from the health plan, or end of the study period.