Maternal and perinatal mortality remain high in the US despite growing rates of prenatal services and spending, and little rigorous evidence exists regarding the impact of prenatal care intensity on pregnancy outcomes. Patients with an expected date of delivery just after their 35th birthday may receive more intensive care owing to the advanced maternal age (AMA) designation; whether this increase in prenatal care is associated with improvements in outcomes has not been explored. To determine the association between the AMA designation and prenatal care services, severe maternal morbidity, and perinatal mortality. This cross-sectional study used a regression discontinuity design to compare individuals just above vs just below the 35-year AMA cutoff, using unidentifiable administrative claims data from a large, nationwide commercial insurer. All individuals with a delivery between January 1, 2008, and December 31, 2019, who were aged 35 years within 120 days of their expected date of delivery were included in the study. Analyses were performed from July 1, 2020, to February 1, 2021. Individuals who were aged 35.0 through 35.3 years on the expected date of delivery were designated as AMA. Outcomes were visits with specialists (obstetrician-gynecologists and maternal-fetal medicine), ultrasound scan use, antepartum fetal surveillance, aneuploidy screening, severe maternal morbidity, preterm birth or low birth weight, and perinatal mortality. The analysis included 51 290 individuals (mean [SD] age; 34.5 [0.5] years); 26 108 individuals (50.9%) were aged 34.7 to 34.9 years and 25 182 individuals (49.1%) were aged 35.0 to 35.3 years on the expected date of delivery. A total of 2407 pregnant individuals (4.7%) had multiple gestation, 2438 (4.8%) had pregestational diabetes, 2265 (4.4%) had chronic hypertension, and 4963 (9.7%) had obesity. Advanced maternal age was associated with a 4.27 percentage point increase in maternal-fetal medicine visits (95% CI, 2.27-6.26 percentage points; P < .001), a 0.21 unit increase in total ultrasound scans (95% CI, 0.06-0.37; P = .006), a 15.67 percentage point increase in detailed ultrasound scans (95% CI, 13.68-17.66 percentage points; P < .001), and a 4.86 percentage point increase in antepartum surveillance (95% CI, 2.83-6.89 percentage points; P < .001). The AMA designation was associated with a 0.39 percentage point decline in perinatal mortality (95% CI, -0.77 to -0.01 percentage points; P = .04). In this cross-sectional study, the AMA designation at age 35 years was associated with an increase in receipt of prenatal monitoring and a small decrease in perinatal mortality, suggesting that the AMA designation may be associated with clinical decision-making, with individuals just older than 35 years receiving more prenatal monitoring. These results suggest that increases in prenatal care services stemming from the AMA designation may have important benefits for fetal and infant survival for patients in this age range.