Health Services/Policy
Quasi-Experimental Evaluation of Michigan’s Prenatal Syphilis Screening Mandate Expansion Meredith Cahill* Meredith Cahill Cahill Michigan State University
Michigan’s congenital syphilis incidence increased by over 1000% from 2012-2023, mirroring national trends. Because testing and treatment during pregnancy can prevent most cases of congenital syphilis, prenatal screening is a key prevention strategy. In 2019, Michigan expanded its prenatal syphilis screening mandate (MCL §333.5123), adding a 3rd trimester screening requirement to the existing 1st prenatal visit requirement. We evaluated the impact of this expansion on Michigan’s congenital syphilis incidence using a synthetic control design. We constructed a state-year panel (2012–2023) using congenital syphilis incidence data from the CDC and natality data for Michigan and 18 U.S. states that maintained the same screening requirement as Michigan’s pre-expansion requirement across the study period. We fit a synthetic Michigan using pre-expansion log-transformed congenital syphilis incidence and the percentages of Medicaid-covered births and births receiving first-trimester prenatal care. We estimated post-expansion effects as differences in log incidence and reported them as percent change beginning in 2020 to account for gestational timing. The synthetic control closely approximated Michigan’s pre-expansion trends (root mean squared prediction error [RMSPE]=0.19; Figure 1). Post-expansion divergence modestly exceeded pre-period error (post/pre RMSPE ratio=1.23). Initially, Michigan’s mandate expansion appeared to increase congenital syphilis incidence by 19% (2020) and 20% (2021) relative to the synthetic control, but in 2022 the trend reversed and incidence was 32% lower. Augmented synthetic control models and placebo tests supported the robustness of these findings. Our study provides one of the first quasi-experimental evaluations of state prenatal syphilis screening mandates and offers initial evidence of the population-level effects of expanded state screening requirements amid the current congenital syphilis epidemic.
