"Screening tests can have what we call false-positive results where other things can interfere," Robinson told WAFF news.
"You can have a substance that a patient eats. Like in this case, poppy seeds can make them test positive for opioids."
Poppy seeds are actually derived from opium poppies and, while they can't get you high, they can sometimes contain traces, and morphine, and could show up in a sensitive drug test.
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Tests also showed that Hernandez's son had no opiates in his system.
Crestwood Medical Center refused to comment on why Hernandez was initially tested but said that it is "committed to following the law and regulatory requirements as well as ensuring the health and safety of our patient".
After she was reunited with her son, Hernandez spoke to WAFF through a translator, saying the experience had been a "nightmare".
"A newborn baby has to be close to mom," she said. "They have to be with the mom."
"That's the most important time in their life to be close to the mom when they're just born."