Final answer:
Pregnant women should be tested for syphilis at the first prenatal visit, and those at high risk should be tested again during the third trimester and at the time of delivery. Penicillin is prescribed to prevent transmission to the fetus.
Step-by-step explanation:
Pregnant women should be tested for syphilis at the first prenatal visit. This is because syphilis can be transmitted from a mother to her baby during pregnancy and childbirth, resulting in serious complications. Women who are at high risk of syphilis should also be tested again during the third trimester and at the time of delivery. If a pregnant woman tests positive for syphilis, she will be prescribed the antibiotic penicillin to prevent transmission to the fetus.