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PHILADELPHIA (CBS) — A Texas woman had a rare delivery– she gave birth to twin baby girls almost a week apart.

Elliyanna Irene was born on Jan. 13 in Longview, Texas. Her sister, Jewlianna Gean was born on Jan. 20.

Their mother says her water broke early before the due date.

Credit: CBS

Doctors say the second baby was not in distress and they wanted the baby to stay in the womb longer because she was premature.

They say the second baby was able to delay birth because the mother had a vaginal delivery instead of a C-section.

Doctors add this is a rare occurrence, it only happens on average: 1 in 1,000.