Large head small femur 36 weeks - should I be worried?

[worryingyetagain]

At my 20 week scan my baby had large head measurements (around 90th centile) but the femur length and abdominal measurements were average (bang on 50th).

I've had other scans since then for various reasons, at 28, 34 and 36 weeks. Looking back at the scan reports the baby's head measurements have always been on the large side, the abdomen always around average but the femur, while still growing, seems to be falling further and further behind.

At the 36 week scan the head measurements were 90th centile and the femur only 10th. I discussed it very briefly with the sonographer and he wasn't worried because the measurements were still increasing and were in normal range.

Now I've googled (bad idea) and am panicking having read about this being a marker for DS and dwarfism. I also noticed that the amniotic fluid level was relatively high at 34 weeks (90th centile ish).

Anyone have anything similar? Am I worrying unnecessarily or should I be concerned? Help please!

I'm sorry I haven't experienced anything similar but I would feel reassured that your sonographer wasn't worried. They will have been trained to look for markers of conditions such as DS and dwarfism and what kind of ratios, percentiles or increasing/ decreasing growth patterns most commonly indicate a problem. So whilst they can't do so with 100% accuracy I would guess they will have been looking to spot anything that might suggest your baby isn't okay and so if they think it's nothing to worry about it probably isn't.

That said if you are genuinely concerned and worrying about this maybe it is worth discussing it with your midwife who can either put your mind at rest or, if she also feels it could indicate a problem, refer you for another scan.

My ds was measuring small on his femur measurements, I asked my consultant about it because I was worried and he laughed and said it means he might have little legs. His legs were on the shorter side but not noticeably so. He now wears the correct size trousers for his age so I assume his legs are average size now

My son was pretty much exactly how you described - measurements wise. I also had polyhydramnios (too much fluid). My son is now 2, totally normal, bit shorter than average but well within 'normal' range

Thanks so much for the responses. mrs and female it's reassuring to know you had similar measurements and all was fine.

It seems so odd to me as DH and I are both average height, neither particularly short. And I can't get over the head/femur ratio, I read on some website or other that it was a bad sign...

Argh I wish I could stop worrying. mynew I'm wondering about phoning but it's so late in the pregnancy now anyway.

I'm 5'6" but have really short legs. DS inherited this, along with my Dad's massive head. I can't remember his femur measurement, but I remember it suggested short legs, and his head was 98th percentile! He's actually very tall for his age, but has short legs (and a big head).

soloman yep, to be honest the more I think about it the more I realise that's kind of me too...I have quite a big head and short legs with a long torso. I'm also 5'6".

Do you think I can be reassured that the femur is still on the 10th centile, at least? My hospital doesn't seem to worry unless it's under 5th or over 95th. But I'm conscious that I'm now v close to those in both directions.

Sigh. I never realised I'd worry so much in pregnancy.

Bumping just in case...

those scans are very inaccurate. I had one I think at 36 weeks, where they told me DD had 98th percentile head. She was born with a slighly below 50th one.

Thanks Katharina. There seem to be so many stories like that, it's amazing how far off the mark the measurements can be! Ultrasounds are amazing in some ways but they're obviously not foolproof.

I'm trying really hard to keep busy and not go too far down the rabbit hole. But I found a study which said that the slowing down of femur growth after 25 weeks, plus the larger than average head, can be a marker for achondroplasia (most common form of dwarfism). It worried me a lot.

Id try not to worry, especially if the sonographer wasn't concerned. When I was pregnant with DS I had to have a bunch of growth scans, on all of them he had really short femurs (literally at the smallest end of the scale) and a giant head. When he was born his head circumference was 1 or 2cms from being 'too big'. He's 2.5 now, still has short legs but none of the family are particularly tall and his head doesn't look too big for him and he's totally healthy

My son had a head on a similar percentile and Femur, not so much.

He's now 7, above average in height and has a head of a 10 year old! But I have a larger head, and hats are rather snug. So it's just his body shape.

The scans work in MM. If the scan is a couple of MM out, imagine how skewed the results could look.

Remember, the percentiles are what's normal. Your son is within the normal range for everything.

My current pregnancy, my baby was towards the bottom end for everything. I worried, and panicked about her having Dwarfism etc then realised that the person doing my scan was a Fetal Medicine Specialist, as I was under consultant care for something else, and he would se le abnormalities daily compared to what I would see. So any concerns would have been raised and another scan brought forward.

Please don't worry. Of course, speak to your midwife to reassure you, but I am certain they would have highlighted any concerns at past scans.

Same as my son. He has just inherited my mahoosive head and stumpy legs..

Hi, can you please let me know how you got on? Was everything ok with your baby? I'm in a similar position and really worried. Thanks

Help! I had a scan on Friday and the measurements are all (apart from HC) coming up small (HC measuring like 2 weeks ahead everything else 2 weeks behind) but the sonographer said they are all in the curves (at different places) so not to worry. On the EFW chart the baby was on the 5th centile at 20 weeks so I was referred to consultant. 28 and 32 week scans showed good growth (moved closer to the 50th centile line) and midwife said it will just be a small baby as long as she continues to go up the curve nothing to worry about. At my scan on Friday (36 weeks) the baby had gone down to the 5th centile line again (although the sonographer didn’t plot it on the chart so I only noticed when I got home that evening). She has gained about 500g in the 4 weeks since my last scan but I am worried now that she is not following the curves.... is this a sign of FGR/IUGR? I have a midwife appointment tomorrow but she always dismisses my concerns so I’m worried she won’t take me seriously! xx

@worryingyetagain Hi, I am 32weeks pregnant and have simillar issue with the baby’s measurements.
How did your experince end up? Did baby have any issues? Hopefully your baby and you are healthy and well.

@Trcnchi I’m the OP! Annoyingly MN won’t let me change my name back to prove it but I got a notification when you posted.

I now have a very normal-sized 7 year old 😊 She has always been on the shorter side, but not unusually so. She does also have a larger than average head (takes after me!)

Hopefully you will also have a good outcome. I’ve since had two further pregnancies and had worries with both of them, scans are amazing in many ways but they can also make you think the worst.

@squirrelsareeverywhere
Thank you sooo much coming back to me. It is great to hear that you haven’t had any issues and hopefully my experience will be similar.
Everything was absolutely fine in 20 weeks scan than after 32weeks, all the measurements get a bit wierd and it doesn’t help to my anxiety.

Thank you for your reassurance Xx