In the past, women were routinely weighed at every pregnancy visit. It was thought that by detecting a sudden increase in weight (or not enough weight gain) it may be possible to identify potential health concerns for the pregnancy or baby. For example, a sudden increase in weight gain could indicate fluid retention (oedema) and possibly high blood pressure, or perhaps having a larger or smaller than average baby.
Research looking at the routine weighing of pregnant women has not been able to find any substantial benefits for either the woman or her baby (nor any medical reasons) to justify monitoring this throughout pregnancy. In fact, the only thing frequent weighing seemed to achieve wss creating unnecessary anxiety about not putting on enough or putting on too much weight.
Be aware, it is fairly common for caregivers to ask you to weigh yourself as part of your first pregnancy visit. This is aimed at having a baseline weight in case the doctor needs to prescribe drug dosages calculated on your average weight at some stage later in the pregnancy or during labour. However beyond this, weighing during pregnancy becomes a little irrelevant. Even so, some caregivers still continue to weigh women as part of their routine antenatal visits. Or women ask to weigh themselves out of interest.
You can read more in weight gain during pregnancy.