A woman had spontaneous quadruplets. The chances of this happening are one in 1 million, a doctor said.

• Madison Collier wasn't on any fertility drugs when she conceived quadruplets.
• The babies are now 4 months old, and Collier says life is busy.

Last year, Madison Collier, a reading teacher in Georgia, went in to confirm her pregnancy with an early ultrasound at about eight weeks. It was all routine until the doctor informed Collier that he didn't see one baby in her uterus. He saw four.

Collier's first clue that something was unusual was when the doctor asked if she was on any fertility drugs. She wasn't. Collier's husband, Justin, had stayed home because he was dealing with allergies. So Collier was alone at the appointment, and her mind started racing.

"I'm like ohhh nooooo not twins!!!! And he goes no, not twins. And then I'm confused.. I'm literally thinking.. they come in more than that???? Now I'm panicked," Collier wrote in an Instagram post.

Collier told Insider that she started hyperventilating, but she still wasn't sure the doctor was telling the truth. "I honestly couldn't believe it until he showed me on the screen," she said.

Sharing the surprise

Convinced that she was carrying four babies, Collier called Justin. He had to lie down on the floor because he felt faint.

"It's literally the shock of a lifetime," Collier said. He added that "no one expects quads," especially "not natural ones."

The Colliers' older daughter, Isla, was 3 at the time and curious about what was going on, with her dad lying on the floor and her mom crying on the phone. Justin told her she was going to have four younger siblings instead of one.

"She said, 'Do we have a plan for four babies?'" Collier said. "And Justin told her that we did not."

One in 1 million

There are only about 150 sets of quadruplets and higher-order multiples born in the United States each year. Most often, they happen when a parent has been using assisted reproduction. Collier wasn't being treated for infertility, and she and Justin have no family history of multiples.

Dr. Kecia Gaither, an OB-GYN, said the chances of spontaneous quadruplets fall somewhere between 1 in 700,000 and 1 in 1 million. A quad pregnancy can occur when multiple eggs are released, or when eggs split. Collier's quads are two boys and two girls. But since the babies all had their own placenta, it's unclear whether any of them are identical twins. A simple genetic test could confirm whether they're identical.

Carrying four babies increases the risk for complications to both mother and babies. One of the most common complications is preterm birth. Collier experienced that when the quads were delivered at about 28 weeks of gestation. The babies' weight ranged from 2 pounds and 5 ounces to 2 pounds and 10 ounces, and they needed to stay in the neonatal intensive-care unit.

Life with 5 kids

Today the quads — Calloway, Eliza, Iris, and Wilder — are 4 months old. A typical day involves changing about 30 diapers and feeding the babies every three hours.

"It's a lot of work, but they're very sweet," Collier said. "Sometimes they support each other in crying, so it gets really loud occasionally."

Even before the babies were conceived, Collier's ability to work was limited because Isla has juvenile arthritis and needs frequent medical appointments. The family has started a GoFundMe to help with the expense of their suddenly much larger brood, and Collier is settling into the family she never imagined.

"They're actually really good babies," she said. "They've started to smile and make sweet cooing noises. It's the best!"