Ms. Beltran thought she was being helpful when, in her first prenatal visit, on July 2, to a clinic at St. Joseph’s Hospital, she discussed her medical history. Ms. Beltran, who worked as a bartender and waitress and became pregnant by a boyfriend who remains close, told the physician assistant that she had become addicted last year to Percocet, a painkiller. But she had willed herself off it the previous fall, even going to the hospital in November for withdrawal symptoms.