The first movements are so small that many people aren't sure at first. Here's how the NHS and others describe them, how they change, and when not having felt anything is a reason to call.
How people describe them
The NHS describes the very first movements as a fluttering or bubbling, or a very slight shifting movement. Early on they can feel like a gentle swirling or fluttering (NHS, Tommy's).
Butterflies, bubbles, a swish. Pregnancy, Birth and Baby lists fluttering (like butterflies in your tummy), bubbling, swishing, rolling, tumbling or tiny kicks. Light tapping. East Kent Hospitals NHS says first movements are hard to describe, but can feel like bubbles, light tapping or a swish. Quickening. These first sensations are also called quickening (Pregnancy, Birth and Baby).
Is it wind, or my baby?
Early on, it's easy to mix the two up. The NHS week-by-week guide says that a bubbling feeling you might think is wind could be your baby moving.
You're most likely to notice movements when you're sitting or lying still, and less likely when you're busy (RCOG).
When they usually start
Most women first become aware of their baby moving at 18 to 20 weeks (RCOG). The NHS gives a wider window, between 16 and 24 weeks.
In a first pregnancy, you may not notice movements until after 20 weeks (RCOG, NHS). If you've been pregnant before, you may feel them as early as 16 weeks (RCOG, Tommy's).
When will I feel my baby move? covers the timing in more detail.
How they change
As your pregnancy goes on, you may feel kicks and jerky movements (NHS). Later on, the NHS says, you can't mistake the movements, and you can even see your baby kicking about.
Movements build until about 32 weeks, then stay roughly the same until you give birth (Tommy's, RCOG). The week-by-week guides follow them stage by stage.
If you haven't felt anything by 24 weeks
If by 24 weeks you have never felt your baby move, contact your midwife or maternity unit (RCOG). And once you've been feeling movements, if they slow down, stop or change, contact your midwife, doctor or maternity unit straight away. What to do.