Kristen and Ian Miller just celebrated their first wedding anniversary in the NICU of University of Tennessee Medical Center in Knoxville. The couple has spent every possible waking moment there since their son, Micah, was born on Valentine's Day.

"The only thing that's gotten me through this... is to say, 'God is in control,'" said Kristen Miller, 27, of Jefferson City, Tenn.

Micah was born nearly four months before his and his baby sister's due date in early June. Kristen and Ian found out they were expecting twins after just a few months of marriage.

Their doctor looked at the ultrasound and asked if twins ran in their family.

"We, of course, said no. By then, we were kind of like, 'What's going on?'" said Kristen.

"She [the doctor] said, 'Well, you do now!'" said father, Ian Miller, 27.

Kristen had no complications with her pregnancy until she started feeling contractions during a church service. By the time she got home, her water had broken.

"She called me hysterical," Ian said.

Doctors held off labor for two more weeks using a variety of treatments and drugs.

"Our goal, before he was born, was, 'we’ve got make it to 24 [weeks]!' Sure enough, he made it to 24 and one day," Ian said.

Twenty four weeks is the maturity doctors say a baby needs to reach to survive outside of the womb, but even then, the risk of complications are high.

"There were 18 people in the operating room with us," Ian said.

"Just because we're having one [baby] doesn't mean we have to have the second or the third. But it's hard to find the person who's a really good candidate," said Dr. Kristina Shumard, a Maternal Fetal Medicine obstetrician at UT Medical Center.

Dr. Shumard was able to stop Micah's twin from coming. But she was not hopeful. She expected the second baby to come within the hour.

Kristen and the twins turned out to the perfect candidates for delayed interval delivery, where twins born at different times. The twins had separate sacs and placentas. The delay typically lasts anywhere from an hour to a week.

Doctors explained to the Millers the developmental benefits of a baby staying in the womb as long as possible.

"We said, 'Yes, if there's anything you can do to keep one of them in longer, we want to do that.' They all said, 'Yes it's possible,' and hinted that it was unlikely.

Kristen's team of doctors put her on strict bed rest. She wasn't even allowed to hold Micah for three weeks.

"I think all of us had counseled her so cautiously. And tried to frame their expectations, but instead she kept doing better each day. And we just kind of all looked at each other and said, 'Ok, another day it is," said UT Medical Center's Director of Obstetrics, Dr. Kimberly Fortner.

"We made it five and half weeks before Madelyn decided she wanted to come into the world. Thirty-eight days," said Kristen.

The Millers had the longest interval delivery in both doctor's career and the longest in recent memory at UT Medical.

"I don't know that we've broken national records, but it certainly felt like such a coup for all of us," Dr. Fortner said, "It's been amazing and exciting!"

Madelyn is breathing on her own and is growing in the same room as her big brother.

For at least two more months, the NICU room is home for the Millers and that's alright with them because they are together, a family of four.

“We feel so blessed to be here,” said Kristen.

Both babies are doing as well as to be expected for preemies of their size. Interval deliveries typically do not last longer than a week and are rare.

Doctors at UT Medical can only recall one other instance of twins being born more than five and a half weeks apart.