Four US states have enacted laws for more frequent syphilis screening during pregnancy and childbirth. These measures led to an increase in the detection rate of prenatal syphilis cases. However, the effect diminished in the year after the laws took effect. In a study of 170,005 pregnant women aged 18–49, 79.6% had been tested for syphilis at least once. 95.1% of women lived in a state with mandatory testing during pregnancy. Women in states with laws were 14% more likely to be screened. Most of the tests took place in the third trimester, and most of the test subjects completed at least two tests. Despite CDC recommendations, screening did not reach 100% even in insured populations.