37th percentile

[tryfor2]

I had my mid-pregnancy ultrasound at 19w3d. The sonographer said everything looked good, that the baby was measuring just one day behind. This surprised me a little since my dates are based on ovulating/conceiving on Day 14, not Day 21 as I know to be true (temp, OPKs, timing of BD). So I figured the baby may be a little on the larger side.
I saw my OB today and she gave me a copy of the u/s report. She said the baby was measuring fine. I looked at the report when I got home and noticed that it said the estimated fetal weight (at 19w3d) was 283.9 grams which is the 37th percentile (according to the report).
This seems low to me. Maybe I'm oversimplifying but wouldn't "normal"/average be around the 50th percentile? I don't know what my toddler son weighed in utero at this stage so I can't compare, but since birth he's always been in the 85th+ percentile for weight and height.
I obviously can't ask my OB about this until my next appointment in four weeks, so I'm wondering if any of you know what your babies weighed at a similar gestation and what percentiles they were in. Trying not to obsess here...!

 

[tryfor2]

Meant to say that 283.9 grams is 10 oz.

 

[Yo_Yo]

Really don't stress over it. These things are estimated. When I was pregnant with dd2, I had to have growth scans as on fundal height she was measuring small-several scans predicted to be low birth weight, and even the final scan a week before she was born said she would be 5lbs at birth, and she was 7lbs 7oz!
My midwife this time around rolled her eyes when I said this had happened, and said they commonly are way out.

 

[the why bird]

The whole point of percentiles is to give an idea of where babies lie compared to other babies. If he's 37th, that means 36 out of every 100 will be smaller than him. It's not something to worry about.

As for him measuring a few days ahead of where you were expecting, they might have just caught him at the end of a growth spurt. Like children, babies can grow in uneven spurts.

It's a pretty inexact science too - a slight variation in position or a different tech could mean a different result and tiny changes in measurements make a big difference. They really just check these things to make sure that baby falls broadly within normal range. They would only worry if he was extremely big/small for gestation, drastically changed percentiles or showing no growth.