England, police said on Tuesday.
Police said the arrest came after an inquiry into the deaths of 17 babies and 15 "non-fatal collapses" between March 2016 and July 2016 at The Countess of Chester Hospital's neonatal unit.
"This is a highly complex and very sensitive investigation and, as you can appreciate, we need to ensure we do everything we possibly can to try to establish in detail what has led to these baby deaths and collapses," said Detective Inspector Paul Hughes.
Police did not give further details about the arrested woman or their investigation.
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