If you notice a pregnant woman suddenly put her hand to her abdomen and smile, chances are she just felt the flutter of her fetus. Future moms first experience the acrobatics going on inside the womb around the 16th to 20th week of pregnancy (women who've been pregnant before often notice movement sooner simply because they recognize it as such, not digestive gurgling).
These early sensations, called quickening, resemble slight tickles; as the fetus grows, the movements metamorphose into definite kicks and nudges, which tend to be most pronounced during the evening and early-morning hours, a fetus's most active periods. As the pregnancy nears its end and the baby has less room to rock, expectant moms may feel a stretching sensation rather than a discernable kick.
But a significant change in activity may signal a complication, such as an infection or cord problem. "A fetus that's not well will move less. Mothers should pay attention to their baby's activity, particularly in the third trimester," says Vanessa Barss, M.D., associate professor of obstetrics and gynecology at Harvard Medical School. If you notice a change, lie down and count how many times you feel the baby move. If you don't feel five pokes, kicks or wiggles within two hours, inform your doctor. She may order tests to check on the baby.