According to WebMD, women usually first feel their unborn baby move between 16 and 25 weeks. First pregnancies typically take longer for the woman to start feeling movement. In subsequent pregnancies, prospective mothers are likely to notice movement sooner, perhaps even as early as 13 weeks.
WebMD notes that fetal movement is easier to detect when a woman is sitting or lying down. Early in the pregnancy, movements are light and twitchy. By six months, strong kicks are often felt. During the third trimester, the fetus starts shifting about 30 times per hour. Movements tend to peak between 9 p.m. and 1 a.m. due to variations in blood sugar levels.