Baby gets a growth gene from one of their parents... So, if both parents were small babies, your baby would be small. If both parents were big babies, the baby would be big. If one parent was big and the other small, it could go either way. Of course, there are other factors that could change this, like GD/diabetes or other things, but this is a guideline...
Your baby being smaller right now probably means that they got a growth gene from a parent who was a small baby. It could also mean that the measurements are off and that baby is larger than appears... It could also mean that your baby has a growth spurt coming up soon. Either way, if baby had plenty of fluid and plenty of room and was just smaller than average with no problems, I wouldn't worry at all!
In my experience dating at scans is not that accurate. You say you were behind 3-4 days at your earlier scans, this could be because you ovulated late etc. So really you're only 3-4 days behind that. My 20 week scan pics said dates were accurate within 1 week and 3 days either side so not accurate at all.
Also I have gone from measuring a week ahead to a week behind to a week ahead again. I really think babies just grow in spurts so maybe you're about to have one.
Also I have a friend who measured around 3 weeks behind all the way through and her little one was perfect just a little smaller than the "norm" when he was born.
Finally another friend had a scan at 36 weeks and was told her baby had a normal head but his abdomen was much smaller and there was a growth problem. Well he was born and he is perfect no issue whatsoever.
From all I know about scans I wouldn't rely on the measurements too much as long as baby looks healthy please try not to worry - now I only need to take my own advice as I might not worry about dates but I do worry about more or less everything else ;-)
I agree with the above posters. I wouldn't worry at all about this. I doubt that your baby is "behind." It's probably more like they were wrong when they dated your pregnancy in the first place. But it's easier for them to say it's the baby being slow than admit they were wrong!
The last scan for my daughter, they measured her at about eight pounds. She was born a week later at 10 lb 7.2 oz. I've learned not to take scan reliability too close to heart. Try not to worry; these things aren't always accurate! My doctor swore up and down she'd be average weight (I felt huge); they really don't like admitting they're wrong! :0)
We just had ours last week at 18 weeks and they said she is measuring at 17 weeks - at our 12 week scan they put us ahead by a full week because she was so much bigger. (That actually the date I agree with though because I know when I ovulated).
But I was only just over 5lbs, and so was my husband and he was a week overdue!! So I wouldn't expect our little girl to be big.
My other girls all measured small as well, and they were 6lbs 2oz consecutively for the first two and 7lbs 3oz for the third - so not big babies.
I wouldn't worry too much - they grow at different rates just like they do once they are out of the womb!
My son is turning 8 next month and he's only on the 3rd percentile - don't stress too much!!!
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