My baby was initially classified as small, although not picked up as early as yours, we had a lot of extra input, and then on the most recent scan it’s been normal again and so that has all been scaled back.
As the previous poster has said, it could simply be that your baby is just small.
Centiles are just that, they do not give an overall indication of the wellbeing of a baby, just where they fall size wise within the ‘averages’.
If you had 100 healthy baby’s. 1 baby would be the smallest, 10 would be classified as small. 10 would be classified as big, and 1 would be the biggest. But they’re all still healthy baby’s.
So the charts plot the baby within the averages. (Is it a customised growth chart? As that would quite possibly give a different answer altogether. That said, the only customised growth charts I’m aware of start at 24/40)
Your baby may simply be ‘physiologically small’. It happens. It has to.
But equally, there could be a reason that your baby is small and therefore why it plots small on the centile chart. And this is what needs to be determined if possible. The centile chart give HCP indications for doing closer or further monitoring and tests- essentially they’re a red flag for further information finding.
At 20 weeks it’s quite early in terms of determining what’s going on and you may find it takes a while to get any clear indicators, if there are any.
It’s easier said than done, but try not to worry too much at this stage, see what happens with your next scan and then if/when you have further follow up.
Write down any questions you may think of between now and your next appointment, as it’s easy to think ‘I’ll ask that’ and then forget.
Try not to find blame in anything you’ve done, or haven’t done. Speaking from experience it’s very easy to think what if what if what if, but that won’t help how you feel or change anything.