MINNEAPOLIS, MINN. ? A sextuplet born prematurely to a Minnesota couple has died, and his five siblings were in critical condition, hospital officials said Thursday.

Bennet Ryan Morrison died Wednesday night, and the other babies remained in critical condition Thursday at the neonatal intensive care unit at Children’s Hospital in Minneapolis.

The Minnesota sextuplets, born Sunday, were one of two sets born within 10 hours of each other this week. In Arizona, Jenny and Brian Masche became parents to six babies on Monday. Doctors say it was a rare occurrence, but one that could become increasingly common as more couples seek artificial methods of conceiving babies.

Parents Ryan and Brianna Morrison, both 24, of St. Louis Park, spent more than a year trying to conceive before Brianna started taking fertility drugs.

The Morrison sextuplets – four boys and two girls – were born about 4 1/2 months early. Their weights ranged from between 11 ounces to 1 pound, 3 ounces, according to a hospital spokeswoman.