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How reliable are pre birth measurements and weights from scans?

(13 Posts)
misssmilla1 Wed 22-Jul-15 15:51:36

I'm 31 weeks and had a regular scan this morning at my Drs. Everything is fine, but measurements she took show that the baby is coming up large.

His femur length is 2 weeks ahead at 33 weeks, and his weight is a bit more than they'd expect at this point at just over 4lbs. She had no cause for concern but was basically flagging it as they will continue to check at every scan and if he continues in the same vein, at some point (when he looks like he's measuring about 10lb) they stop considering vaginal birth as an option.

I think the femur length must be pretty accurate as they measure point to point, but does anyone know whether the weight can vary?

Nannynome Wed 22-Jul-15 15:56:00

DS1 was predicted to be 8lb 9oz and came out at 6lb 11oz!
DD1 was predicted to already be 8lb 3oz at 36 weeks, she came out at 8lb 2oz at 38 + 3!!

They were both very long and slim.

Wittynewnameifonly Wed 22-Jul-15 15:59:57

Not very accurate and medical studies show that.
DS1 was predicted at 10lbs, turned out to be 9lbs 1oz. DS2 was predicted at 8.5lbs and came out at 10lbs 2oz.

I tried to get extra scans for DS2 so that we could assess size but was pointed to studies showing it is unreliable as an indicator of birth weight.

eaiand2 Wed 22-Jul-15 16:06:22

My bump measured a couple weeks behind as standard throughout my pregnancy, my last scan was at 32 weeks, so nearly 9 weeks before she was born, but at all scans (19, 23, and 32 weeks) they estimated DD to be bang on 50th centile for my dates and a midwife told me I could likely expect an average sized baby of between 7-8lbs. DD was 9lb8!

HazleNutt Wed 22-Jul-15 16:18:50

friend was told baby was really small - was 3,5 kilos.
I was told at 36 weeks that DC2 had a 95th percentile head - had a totally average one

StaircaseAtTheUniversity Wed 22-Jul-15 16:21:20

I have a blood condition so was regularly scanned. At 35 weeks I was told my DD was around 8lb to 8lb 5oz. She was born at 39+6 weighing 7lb 5oz. She was very long though.

Mulligrubs Wed 22-Jul-15 16:22:16

Mine was close, predicted 5lb10oz at 37 weeks, he was born the next day 5lb12oz

Mamabear14 Wed 22-Jul-15 16:23:22

I will let you know over the next few days! I am being induced tomorrow at 39+3 and at just 36 weeks exactly they said she was 7lb 1 with a 95th centile head and a 97th centile abdomen!

misssmilla1 Wed 22-Jul-15 17:07:51

Thanks all. Good luck mamabear!

mygreeneyedboy Wed 22-Jul-15 18:07:04

The week before he was born he was predicted 8lb5 - he was 7lb11!

RiverTam Wed 22-Jul-15 18:10:21

I wasn't told a weight, just that my baby would be small (which I totally didn't believe smile). She came in at 6lbs.

I was told 5 kg (11lb) for ds1 - he was 3.8kg (8 lb 6)

Topsy34 Wed 22-Jul-15 19:20:29

I read one study that indicated a 20% either way from the predicted weight. Im just off out but i will try and find it when i get back

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