Most expectant mothers begin feeling their baby's presence when the fetus starts getting its kicks by booting the lining of its fetal sac after about 20 weeks. That's usually the first sign of movement, but there is evidence suggesting that the tyke is actually moving around long before that.
Those motions, however, are pretty tiny, considering that the new human growing inside might scarcely be longer than an inch, usually around eight weeks into a pregnancy. Women will assume it's gas or an abdominal disorder, and not the proverbial thump they would otherwise expect. What they may actually be feeling during that first trimester is the baby stretching its abdominal limbs or gently wiggling around, a positive sign that indicates the central nervous system is in top gear, getting the body to respond to brain impulses that get the baby to move.
Something that women might feel that's traceable to the baby's actions might start as early as the 18th week. They're often called "flutters," (although most physicians call them "quickening") when the baby's continued stretching and limb movement can be felt in the belly button area, usually at the same vertical level as the uterus at this stage of pregnancy. However, there are plenty of anecdotes from women who've had previous pregnancies and have already become conditioned to feeling baby's movements, who claim to experience those sensations as early as week 12.
But it's more likely that women will be sure that the baby is the source of all of those movements around week 22. It could be a stomach-thumping kick or punch or even the feeling of a scratch, considering that the baby's fingernails are already growing by this stage. Anyone a mother invites to feel her abdomen to check out those movements will be able to feel the motions by the 24th week. Those wiggles and kicks will develop more into backflips and somersaults by the 30th week as the baby is now testing the spatial limits of the womb, which means more intensity in the sensations. From that point on until delivery, the baby will also start rolling around.
However, if pregnant mothers don't start feeling any movement traceable to the baby, they should consult their physicians.