Hospital officials say three of the sextuplets born prematurely to a Minnesota couple have now died. The other three remain in critical condition.

A third boy, Lincoln Sean Morrison, died Friday. Two of his brothers, Tryg and Bennet, died earlier in the week.

The four boys and two girls were born last Sunday about four and a-half months early at a Minneapolis hospital. Doctors had advised the couple to selectively reduce the number of viable fetuses to two, but they declined.

Parents Ryan and Brianna Morrison released a statement saying it's been "a difficult week" for them. They thanked everyone for their prayers and support.

Hospital officials say no further information will be released.

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

Parents Ryan and Brianna Morrison, of St. Louis Park, issued a statement Thursday expressing thanks for the support of families, friends and churches and for the work of hospital staff.

"Our faith remains strong in the midst of mourning our son," the Morrisons said.

The Morrisons, both 24, spent more than a year trying to conceive before Brianna Morrison started taking fertility drugs, and had success with the drug Follistim, according to the couple's personal Web site.

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.