A 28-year-old woman who didn't know she was pregnant was shocked to welcome a baby on Christmas Day.

Melanie Smith told ABC News that for years, she didn't think she could have a child. The author said she was told by a doctor nearly a decade ago that she likely couldn't carry a child because of irregularities with her uterus.

In the early morning hours of Dec. 25, Smith said she experienced stomach pains and initially thought it might be constipation. When the pain didn't subside, she decided to go to a local hospital in Waukegan, Illinois, with her husband Donovan O'Dell.

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"[The pain] kept kind of growing in intensity and frequency," Smith recalled. "By, like, 3:30 [a.m.,] I was like, 'OK, it's time to go to the hospital. Something's very wrong.' And then [we] got to the hospital, and they were just like, 'We're pretty sure you're pregnant.'"

Smith said that about two hours later, she and O'Dell welcomed baby Vincent Antonio O'Dell, who weighed 8 pounds, 1 ounce at birth.

Vincent is the first child for both Smith and her husband, she said.

Smith said prior to experiencing stomach pain and giving birth, she did not have other telltale signs of pregnancy aside from back pain, which she chalked up to a flare-up from cold weather as a result of a back surgery she had back in 2020.

She said she was told by her doctors that she'd had what is known as a cryptic pregnancy, and that Vincent had been "hiding" behind her spine during the pregnancy.

Once Vincent was safely delivered, he and Smith were transferred to Northwestern Medicine Catherine Gratz Griffin Lake Forest Hospital in Lake Forest, Illinois, for further care.

Dr. Adrienne Adams, medical director of maternity services at Lake Forest and one of Smith's doctors, told ABC News there are various factors and conditions that can lead to someone not knowing about their pregnancy.

"If someone has irregular or absent periods at baseline, they may not notice a change," Adams said in a statement. "Symptoms related to pregnancy aren't experienced the same way from person to person, and they may be subtle or easily mistaken for something else."

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Although uncommon, the occurrence of cryptic pregnancies, where a mother doesn't know she is pregnant, has been documented as early as the 17th century, per a 2023 report in the journal Case Reports in Women's Health. In the U.S., as many as 1,600 pregnancies are considered cryptic pregnancies, according to the same report.

According to the American Pregnancy Association, researchers estimate that 1 in 475 pregnancies may go undetected until the 20th week of pregnancy, and 1 in 2,500 pregnancies aren't noticed until a woman goes into labor.

At Lake Forest Hospital, Vincent underwent additional medical testing.

"We didn't get any prenatal care and they just wanted to make sure that everything was 100% for him," Smith said. "But he ended up passing all of his tests, and he got a clean bill of health from all the pediatricians that saw him."

Now, the family of three is gradually adjusting to a whole new life together.

"I had never really thought that I wanted kids and never anticipated that being part of my life plan, especially with the expectation that I couldn't have them to begin with," Smith said. "And now that he's here … I couldn't imagine life without him anymore. And he's only been here a couple weeks."

Since welcoming baby Vincent, the family has moved from Illinois to Arizona to be closer to family.

"[I'm] still [in] a little bit of a shock, but I'm doing great, and my son's just awesome," Smith said.