How Can Women Miss the Symptoms of Being Pregnant?

Women aren't going to use pregnancy tests or pregnancy calculators when they don't think it's possible that they could be pregnant. And it turns out that women who give birth without ever having known they are pregnant haven't lost their minds. They almost always just experience unexpected variations in their anatomy and the activity of their endocrine systems.

• The Pill doesn't always work. It's possible to become and stay pregnant even while taking oral contraceptives. 
• Women who have cryptic pregnancies may have abnormalities in the production of human Chorionic gonadotropin, also known as hCG. This hormone enables the ovary to release an egg during the ovulation cycle and then stimulates the uterus to release progesterone during early pregnancy so it thickens and provides more blood vessels to provide oxygen and nourishment to the embryo. Levels of hCG peak about the same time as morning sickness. If a woman's body is producing less hCG, she may not have morning sickness. However, if she doesn't know she is pregnant and continues taking a high-progesterone oral contraceptive, the Pill may ironically help her stay pregnant.
• Many women who go through cryptic pregnancy develop amenorrhea (irregular periods) that they mistake for menopause. They may even stop using contraception because they think they cannot become pregnant.
• In one study of cryptic pregnancy, none of the women had suffered morning sickness. 
• Women may have a "period" even when they aren't going through their normal ovulation cycle. It's more likely this is due to bleeding associated with pregnancy, coming at irregular times that women assume is due to their approaching menopause.
• The overwhelming majority of women who have undetected pregnancies are psychologically healthy. A study in Europe found that about 5 percent had psychiatric issues like schizophrenia, and about 8 percent were intellectually challenged.

READ Early Pregnancy Symptoms and Signs

• Although the examples cited above involved healthy, normal weight babies, low birth weight babies are more common in cryptic pregnancies. Mothers of low birth weight babies may gain very little or even no weight while they are pregnant. About 20 percent of infants resulting from undetected births weigh less than 2500 g (5.5 lbs) at birth. This may explain why some mothers don't experience morning sickness or abdominal swelling in their pregnancies.
• Women who become pregnant after the age of 35 don't have as much estrogen production during pregnancy. Their breasts may not enlarge. They may not have the "glow" that sometimes comes with pregnancy. 

Even where late-term abortion is available, women who discover they are pregnant late almost never have the procedure. Women who have cryptic pregnancy usually turn out to be "good mothers" in several senses of the term. Babies born after undetected pregnancies, surprisingly, tend to be healthy, despite the fact their mothers did not know to take precautions with medications, radiation, alcohol, and drugs during pregnancy. When there are complications, they are most likely to be due to low birth weight or the surgical procedures needed during delivery.