Throughout pregnancy, the reasons that might lead you to need an urgent assessment also change according to the weeks of pregnancy. A sign that is important at 36 weeks may not yet have the same meaning at 18.
For example, around 18 weeks many women are only just starting to feel their baby's first movements and some will recognise them later. Therefore, at this stage, we do not yet expect there to be a pattern of movements that you can track daily.
As pregnancy progresses, you will get to know your baby and their usual pattern of activity better and better. Later in pregnancy, a clear decrease in movements compared to what is usual for your baby becomes an important reason to seek an assessment.