A federal district court has found that this happened, and that this violated the Constitution. From Bower v. Lawrence County Children and Youth Services (W.D. Pa. Aug. 12, 2013) (some paragraph breaks added):

In July 2009, Bower was a twenty years old resident of Lawrence County, Pennsylvania. On July 12, 2009 at approximately 7:00 p.m., Bower hosted a barbecue dinner at her new home. As part of the meal, Bower consumed linguini salad with McCormick Foods Supreme Pasta salad dressing which contained poppy seeds. Bower used two bottles of the salad dressing with one pound of pasta. Bower Deposition at 127. Shortly after dinner, Bower went into labor. During her pregnancy, Bower had received necessary and appropriate prenatal care and had passed every drug screen that had been administered, including a drug test taken approximately three weeks earlier, on June 22, 2009. At 9:20 p.m., Bower was admitted to Jameson for the birth of her second child. At that time, Jameson had a written drug testing policy (the “Policy”) by which all obstetrical patients were administered a urine drug screen in order to identify newborns who may demonstrate symptoms of drug withdrawal and require special observation and treatment…. The hospital laboratory detection level for opiate metabolites is 300 nanograms/mL, which is far lower than the 2000 nanograms/mL level set by the federal government for federal workplace testing programs. Jameson’s Policy further required that if a mother tested positive, a drug test be performed on the newborn’s urine and meconium. The Policy required Jameson to notify its social service department whenever a maternity patient’s initial drug screen was positive. In July 2009, every initial positive drug screen result was reported by Jameson’s social services staff to LCCYS.

Even though the mother noted the possibility that the positive test result came from poppy seeds, and there was no confirmation that the test result actually reflected drug use (or any other evidence that the mother used drugs), the baby wasn’t returned to the mother until 75 days after the baby’s birth. The court held that the county’s actions violated the mother’s constitutional rights:

[T]he LCCYS policy can result in the separation of mother and child within days of birth without any valid basis for doing so. As illustrated by the timeline in this case, there was no need for precipitous, ex parte court action. Baby Brandon remained in the hospital for several days, during which time LCCYS could have corroborated (or questioned) the initial urine screen result. Indeed, the LCCYS Intake Screening Form noted that there was no present or impending danger. By taking custody of Baby Brandon without any effort to corroborate the drug test and without talking to the parent, LCCYS policy did not provide sufficient protection for the fundamental parental rights involved in light of the drastic nature of the deprivation. The LCCYS action in this case was an arbitrary use of government power which transcended the realm of negligence and deliberate indifference. [Caseworker Eva] Lightel stated: “I have the hospital saying she tested positive and that was enough for me [to get an ex parte order to take the child].” The removal of Baby Brandon based solely on Jameson’s report of the initial urine screen — with no individualized investigation — shocks the conscience and violates Plaintiff’s substantive due process rights.

Pretty appalling. I agree that the law should try to protect children from neglect and abuse by their parents, including that evidenced by a mother’s using dangerous and illegal drugs during pregnancy. And I agree that there will always be some errors in such processes, as in any other human processes. But an error such as this, which endured for 75 days, is much harder to justify.