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. 2013 Jun 26;8(6):e67405.
doi: 10.1371/journal.pone.0067405. Print 2013.

Harnessing the Medicaid Analytic eXtract (MAX) to Evaluate Medications in Pregnancy: Design Considerations

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Harnessing the Medicaid Analytic eXtract (MAX) to Evaluate Medications in Pregnancy: Design Considerations

Kristin Palmsten et al. PLoS One. .
Free PMC article


Background: In the absence of clinical trial data, large post-marketing observational studies are essential to evaluate the safety and effectiveness of medications during pregnancy. We identified a cohort of pregnancies ending in live birth within the 2000-2007 Medicaid Analytic eXtract (MAX). Herein, we provide a blueprint to guide investigators who wish to create similar cohorts from healthcare utilization data and we describe the limitations in detail.

Methods: Among females ages 12-55, we identified pregnancies using delivery-related codes from healthcare utilization claims. We linked women with pregnancies to their offspring by state, Medicaid Case Number (family identifier) and delivery/birth dates. Then we removed inaccurate linkages and duplicate records and implemented cohort eligibility criteria (i.e., continuous and appropriate enrollment type, no private insurance, no restricted benefits) for claim information completeness.

Results: From 13,460,273 deliveries and 22,408,810 child observations, 6,107,572 pregnancies ending in live birth were available after linkage, cleaning, and removal of duplicate records. The percentage of linked deliveries varied greatly by state, from 0 to 96%. The cohort size was reduced to 1,248,875 pregnancies after requiring maternal eligibility criteria throughout pregnancy and to 1,173,280 pregnancies after further applying infant eligibility criteria. Ninety-one percent of women were dispensed at least one medication during pregnancy.

Conclusions: Mother-infant linkage is feasible and yields a large pregnancy cohort, although the size decreases with increasing eligibility requirements. MAX is a useful resource for studying medications in pregnancy and a spectrum of maternal and infant outcomes within the indigent population of women and their infants enrolled in Medicaid. It may also be used to study maternal characteristics, the impact of Medicaid policy, and healthcare utilization during pregnancy. However, careful attention to the limitations of these data is necessary to reduce biases.

Conflict of interest statement

Competing Interests: This work was supported by the Agency for Healthcare Research and Quality (AHRQ) (Grant R01HS018533 to SHD). Kristin Palmsten is supported by Training Grant T32HD060454 in Reproductive, Perinatal and Pediatric Epidemiology from the National Institute of Child Health and Human Development (NICHD), National Institutes of Health. The Pharmacoepidemiology Program at the Harvard School of Public Health receives funding from Pfizer and Asisa. SHD has consulted for GSK and Novartis. The sources of funding and potential conflicts of interest do not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.


Figure 1
Figure 1. Overview of the linkage and cohort identification process; Medicaid Analytic eXtract, 2000–2007.
Figure 2
Figure 2. Hypothetical example of woman-infant linkage by state, Case Number, and delivery date range/date of birth.
CA, California.
Figure 3
Figure 3. Schematic of the primary eligibility period.
Figure 4
Figure 4. Cohort size by eligibility period; Medicaid Analytic eXtract, 2000–2007.
The number of pregnancies in the base cohort (eligible from at least 1 month before the LMP month until the month after the delivery month) is represented in red and the number of pregnancies when additional or fewer months of eligibility are required is represented in blue. The lengths of the eligibility periods decrease when moving away from the vertical axis along the horizontal axis. – indicates the number of months before the LMP and+indicates the number of months after the LMP at which the eligibility period begins, and all eligibility periods continue until the month after the delivery month. LMP, last menstrual period; M, months.
Figure 5
Figure 5. Number of pregnancies contributed to the base cohort by state; Medicaid Analytic eXtract, 2000–2007.
Figure 6
Figure 6. The distribution of maternal characteristics in the base cohort; Medicaid Analytic eXtract, 2000–2007.
A) Age, B) Race, C) Medicaid Eligibility Group, and D) Delivery Year.

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