The Affordable Care Act (ACA) Medicaid expansion increased Medicaid eligibility for low-income adults regardless of their pregnancy or parental status. Variation in states' adoption of this expansion created a natural experiment to study the effects of expanding public insurance on insurance coverage, health care use, and health outcomes during preconception, pregnancy, and postpartum. We conducted a systematic review of relevant literature on this topic, analyzing twenty-four studies published between January 2014 and April 2021. We found that the ACA Medicaid expansion increased preconception and postpartum Medicaid coverage with corresponding declines in uninsurance, private insurance coverage, and insurance churn. There was limited evidence that Medicaid expansion increased perinatal health care use or improved infant birth outcomes overall, although some studies reported reduced racial and ethnic disparities in rates of prenatal and postpartum visit attendance, maternal mortality, low birthweight, and preterm births. Stronger data collection on preconception and postpartum outcomes with sufficient sample sizes to stratify by race and ethnicity is needed to assess the full impact of the ACA and emerging Medicaid policy changes, such as the postpartum Medicaid extension.