Primiparous women with in-state vaginal deliveries, adequate prenatal care, and singleton birth at ≥ 20 weeks (n = 117,779) were classified as ART-treated (linked to ART data from SART CORS, n = 3138); subfertile (not ART-treated but with indicators of subfertility, n = 1507); or fertile (neither ART-treated nor subfertile, n = 113,134).