Nelly Itula, 40, delivered identical twin girls and fraternal twin boys, officials at Sinai Hospital said.
The babies were delivered by Caesarian section. The girls weighed slightly more than two pounds, and the boys weighed slightly more than three pounds.
The babies were being treated at the neonatal intensive care unit at Sinai and were said to be doing fine. The family was expected to return to Nigeria when doctors say it's safe for them to travel.
Itula, a teacher, came to Owings Mills, Maryland, in December to visit her sister when she found out she was pregnant, hospital officials said. She was advised to stay in the United States because of health concerns. Her husband, Frederick Itula, arrived in Baltimore from Nigeria late Saturday. The couple has no other children, and Nelly Itula had been taking fertility drugs.
