For a woman who doesn't think she could be pregnant, many of the classic signs can be explained away. Fetal movement? It could be gas or indigestion. Morning sickness? A stomach virus. Weight gain? Bad diet and lack of exercise. Obese women may not gain noticeable amounts of weight during pregnancy. Women such as Staine, who have had children before, are less likely to miss the signs than first-time mothers, but it's not unprecedented.
Surprise births make for fun stories, and they can often yield healthy babies. But failing to detect a pregnancy presents risks to the health of both the mother and the child. For one, it means missing out on important prenatal testing, monitoring, and vaccinations. It also means the mother doesn't know to avoid smoking, drinking alcohol or doing drugs during the pregnancy.
Explainer thanks Stephen Thung of Ohio State University Wexner Medical Center and Iffath Hoskins of NYU Langone Medical Center.