As the nation’s opioid crisis has deepened, the number of drug treatment centers for pregnant women has grown. But experts and advocates say there aren’t enough services for pregnant women to meet the demand, and many don’t offer the drugs doctors would normally use to treat addiction because they are concerned about the effects they might have on a fetus. And some laws requiring that babies going through withdrawal be removed from their mother’s care can be a deterrent to seeking help, they said.