When did you first realize you were pregnant? When you skipped a period? When you felt queasy one morning? Or was it when you ended up in the ER in full-blown labor, about to give birth?
As odd as it may sound—so odd, in fact, that there's now a reality show about it—approximately 1 in every 7,000 pregnancies is unknown to the mother until the moment she delivers her baby.
That was the case with Amanda Prentice, 34. In a CNN report on surprise births, Prentice explained that she and her husband tried for four years to have a baby—without success. When Prentice's period stopped in the fall of 2011, she attributed it to a history of irregular periods and the intense stress and grief she felt over her mother's recent death. Over the next few months, nothing else unusual happened. She gained about 10 pounds, which she thought was due to drinking too much soda—a habit that also explained all the "gas" she felt.
But one morning this past April, Prentice's husband came home to find her in the midst of a seizure. When she arrived at the ER, doctors determined she was seven or eight months pregnant and would need to give birth right away. The seizure, it turned out, was a symptom of preeclampsia, a serious pregnancy complication that affects blood pressure.
Prentice delivered a healthy baby girl. And her reaction? "I was one of these that was saying 'They've gotta know. They've gotta know.' Now [it's]: 'No, you don't have to know,'" Prentice told CNN.
How can you not know you're pregnant, especially after the first trimester? Experts say a surprising number of factors come into play, including:
A Woman's Weight: Women who are overweight or obese are more likely to have irregular periods, meaning it wouldn't be out of the ordinary to miss a period or two (or more). And depending on their shape, women who are overweight may not notice other obvious physical changes related to pregnancy.
The Placenta: If the placenta is positioned near the front part of the uterus, women may not feel the baby move as much, Dr. Kathleen Brennan, health science assistant clinical professor at UCLA Health System, told CNN. When movement is felt, it is easy to confuse it with gas, even in women who are very far along.
No Morning Sickness: Some women don't get morning sickness, or only deal with very mild symptoms. Morning sickness can also be explained away as a stomach bug or just a side effect of feeling stressed out.
Denial: According to Dr. Sabrina Sukhan, OB-GYN at Pennsylvania Hospital in Philadelphia, there are also women who don't want to be pregnant and unconsciously deny the fact. This is more common in teens, but can happen in older moms, especially women in their 40s who already have kids and aren't mentally prepared to add on to their family.
The majority of women who miss the early signs of pregnancy eventually do realize that they're expecting. But for those rare moms who make it across the finish line without even realizing they were in the race, there's usually a "perfect storm" of physical and psychological factors at play, says Sukhan.
Doctors are especially concerned about surprise pregnancies because it means that prenatal care and other pregnancy precautions—including warnings about alcohol consumption and cigarette smoking—are skipped or overlooked. In Prentice's case, regular prenatal checkups probably would have caught her preeclampsia before it reached such a critical stage.
Another mom who gave birth to a surprise baby, Amanda Burger, 33, of Cedar Falls, Iowa, knows she was fortunate to have a healthy child—and now likes to have fun telling her birth story. After nine months of not much—just a little weight gain and feeling a little "weird"—she remembers hearing her 11-year-old son on the phone at the hospital.
"He was calling everyone and telling them 'My mom's having a baby!'" she told CNN. "And they're like 'No, quit playing jokes!'"