Reports say Elaine Novais, 29, a council worker left her premature babies at their home in Piripá, in the northeastern state of Bahia, Brazil, on Tuesday, June 23.
She had not been gone for long when she heard the girls Anne and Analú crying but by the time she rushed back to their bedroom a huge harm had been caused.
The Labrador and American foxhound cross had brutally attacked the girls. Mrs Novais pulled the jealous dog away from the twins, but it had already inflicted fatal damage on their abdomens.
A nurse who lived nearby performed first aid on the twins. One died instantly from her injuries and the other later died at Maria Pedreira Barbosa Municipal Hospital after going into cardiac arrest.
The devastated mother reportedly collapsed from shock after the death of her babies and she had to be resuscitated at the hospital. Mrs Novais and her husband Regis, 32, had been childless for almost a decade before she eventually conceived.
The dog, described as "docile", is believed to have become jealous after not receiving as much attention since the birth of the babies.
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A family member claimed the dog "was left out in a way, and it no longer had the attention and affection of its owners provided before", reports The Sun.
“That could have caused some kind of jealousy and led the dog to attack the children."
Anne and Analú died one day before their due date, having arrived a month early via cesarean section.
Police are investigating the deaths, but are yet to take testimonies from the devastated parents.