Estimated Fetal Weight

EFW or Estimated Fetal Weight

Here’s an email I received from a UK reader asking about determining Baby’s estimated fetal weight or EFW. Read on for my response!

reader:  Hi, I was just wondering how accurate scans are at estimating weight? I’m 36 weeks +1, and I had a growth and reassurance ultrasound today. Baby was perfect :), and they estimated 7 lbs. This is my 4th child, and the only full-term baby I’ve had was my last. He was 7 lb 10 ozs. I am a little worried this baby is going to be a 9-pounder and that I’m going to have a difficult labour. This is my last baby, so I really don’t want to spend these last weeks worrying over nothing. Any info would be gratefully appreciated. Thanks in advance. I love reading your blog!

wwavb:  I love my UK readers! First, let me say I am happy you found my blog and are enjoying it. Thank you so much for saying so! I hope you’ll spread the word!

Now on to your question. I’m unsure what the discrepancy is in the UK for fetal weight. Our machines may be calibrated slightly differently here in the states. That said, 1 lb +/-  is not unheard of and sometimes can be greater depending on the level of skill of your sonographer and fetal position. These factors can make measuring baby more difficult and less accurate, which is precisely why it’s called “estimated.”

If your baby is at 50% or thereabouts, it means he is average in size and will gain, on average, about
1/2 lb/wk until delivery. If your baby is measuring bigger then average (which I wouldn’t know without seeing the individual % for each measurement), it’s feasible Chunky Monkey could gain a little more each week.

Just know that if this baby ends up being larger doesn’t mean you’ll have problems delivering!



It’s also important to note that if your baby is measuring smaller than average, his or her weight gain will likely equal less than that 1/2 lb/wk estimate. Everyone wants to mentally prepare for what they are going to have to push out which is totally understandable!

Best wishes for a quick and easy labor and delivery! for your questions and pics:)


2 replies
  1. mel jackson
    mel jackson says:

    Hi I hope you had a lovely time on your holidays ,just to say I had a little boy at 38+5 and he was a MASSIVE 8lb 7oz 🙂 not half as bad as I imagined ,many thanks for your help mel

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