Terrified 20 week scan and short femurs

[Mrs777]

Has anyone got any experience with this? Had my scan today and everything is fine all measurements and heart etc but the femurs are measuring the 3rd percentile. I’ve to have another scan (bone) one tomorrow.

There are 2 reasons to find out if the baby has Down syndrome. 1 would be If you would terminate the pregnancy with that information. 2 would be so you can read up and prepare yourself.

If the answer to 1 is that you wouldn't terminate then I'd question the benefit of the amnio

The consultant said yesterday the femurs are on the 5th centile the sonographer said the day before we were on the 3rd, She also said it’s too late for the NIPT test??

Google says the NHS offer NIPT up to 21+6 in some circumstances. It doesn't sound like you would meet these, so the NHS may not offer it, but that doesn't mean you can't pay for one privately if you can afford it. The test still works in late pregnancy.

Would you keep the baby if you found out he has Down's? If yes, do not risk the amnio. You would never forgive yourself if something happened. If you can't go down the NIPT route due to cost, then I would say just continue with the pregnancy and find out when he's born. It will be very difficult, but try to get through it by knowing that you are taking on this emotional burden willingly in order to protect your son from any risk to his life. That is an amazing thing to do.

Also, you could ask about growth scans later. It may be that the femurs catch up and provide you with some reassurance. This happened with one of mine, although the percentile difference was not as great as yours.

we most likely would just continue with the pregnancy but it would be a long stressful few months so I’d rather know now and get my head round the fact.

Can you afford NIPT privately then?

Sorry to hear you’re going through this stress and worry! It’s completely personal choice but I would always want as much info as possible. At 29 weeks we were told that all of my (2nd) baby’s long bones including femurs were measuring very small, around the 1st centile. Even though we are both short adults and our first child was low birth weight and is now only around 15th centile for height, the consultant said it was unlikely not to be an indicator of some chromosomal or genetic issue which was pretty terrifying. So we went ahead with the amnio a few days later.

It took almost a month to get the full test results back during which time we felt very anxious and pessimistic about the pregnancy. However all the tests came back with no issues flagged which was a relief and she was born at 37 weeks, very petite but all in proportion and perfectly healthy.

I hope you are offered regular scans to track the growth and if a private NIPT is an option for you this could offer some reassurance. The charity ARC might have some advice about what tests are available and when it’s safest to do them.

Trying to find a place that does them where I live north Scotland, and my consultant said that it’s too late and won’t give a clear picture.

This was our results, she’s never actually said how bad it is, does anyone have any knowledge on this.

Is this the NHS bone scan? Do you have an appointment with the consultant to discuss?
I don't know specifics about this scan I'm afraid. If you want more help I suggest starting a new thread titled something like "Help me interpret bone scan results, 20 weeks pregnant". That should attract people who actually know a bit more about it.
But if you don't need to wait more than a few days for your consultant appointment I would just wait for that tbh, as it's way better than the opinion of strangers on the internet. I do understand the desperation to know, but it won't actually help much.

Yes it was the nhs bone scan, my consultant didn’t really say anything other than I have to offer the amnio.

Hey @Mrs777, this was me 14 years ago. I was told my ds had abnormal measurements at 20 weeks, 4th centile. I was scanned biweekly after that and every time the centile dropped further. It was a terrible terrible time. I refused the amino. My ds is 13 now and a tall basketball player. A few years later when my second ds was measured and the femures were mentioned I just kissed my teeth and politely declined the growth scans. Appears that is how I cook them.

Are you with a research hospital by any chance? I was with a london hospital with a strong fetal research unit and whilst of coursw it was amazing to have all these experts to hand, it did mean they measured everything and anything.

Take this one day at a time, personally I would not have the amino in your case, other markers of downs would have been present most likely. If paying for a NIPT is an option, I'd do that instead or ask of the hospital can provide one.

Hang in there, we are here to hold your hand.

Hi I know chatgpt is terribly unreliable but I've used it before for interpreting my own bloods and it was fairly accurate - I put in you rpost and the bone scan info and it said this:

"I’m not a medical professional, but I can help you understand what’s on this ultrasound screen and why your friend might have been offered further testing.
What the scan shows

• Gestational age: 18w6d (so almost 19 weeks).
• Estimated fetal weight (EFW): 267g (9oz), within normal range for this stage.
• Head and abdomen (HC, AC): Both around 19 weeks, appropriate.
• Femur length (FL): 26.8 mm, corresponding to about 18w1d — this is shorter than the average for her dating, around the 5th centile (low end of normal).
• Other long bones (tibia, fibula, humerus, radius, ulna): Mostly in the 17th–38th centiles, so within normal range.
• Cerebellum (Cereb): Corresponds to 20w1d, reassuring.
• Ventricles (Vp): Normal at 8.1 mm.

Why short femur matters

• Short femur length on its own can sometimes be a “soft marker” for chromosomal conditions like Down’s syndrome (trisomy 21).
• But it is not very specific — in many cases, it simply reflects normal variation, a constitutionally small baby, or sometimes later growth restriction.
• Importantly, other major markers aren’t seen here (nuchal fold thickening, heart defects, absent nasal bone, echogenic bowel, etc.).

NHS approach

• In the UK, when a single soft marker (like a short femur) is found, the sonographer usually refers the case for review and counselling.
• If your friend already had low-risk results on the combined screening or NIPT, the chance that this isolated short femur means Down’s is still quite low.
• Amniocentesis is offered because it is the only diagnostic test that can definitively rule in/out chromosomal conditions, but it carries a small risk (about 0.1–0.5% chance of miscarriage).

Key reassurance points

• The femur length is just below average but not absent or severely shortened.
• Other bones and brain structures are measuring normally.
• Isolated short femur is more often linked to small but healthy babies than to Down’s.

✅ Next steps: Your friend may want to discuss with the fetal medicine team:

• Whether non-invasive prenatal testing (NIPT / Harmony / Panorama) is an option if she hasn’t already had it (this is highly accurate and carries no risk).
• Whether they think this finding is truly isolated, or if they see other subtle concerns.
• Pros and cons of amniocentesis given her already low-risk screening.

Would you like me to explain how the percentile numbers shown on this scan (e.g. femur 5%, head 38%, cerebellum 59%) relate to how “big a deal” the finding is? That might help make the picture clearer."

As an aside I've not had the short femur personally but one of my DC they were absolutely sure that he was going to be a gigantic baby ans they were extremely concerned about his stomach and head which was measuring large, off the percentiles! They were extremely serious and scary about the risks - I had lots of growth scans and they were pushing for induction early or section- but thankfully dc came bang on 38 weeks. Totally normal stomach however did have a large head and still does 😬

Oh no I really feel for you. We had this with DS, I was 43 and they never really said what they suspected but I guess Down syndrome. His measurements were really similar to yours ie. everything fairly average except femurs which were about 3rd percentile.

I was referred to fetal medicine and they did a very detailed scan and said they thought everything was ok but wait and see.

He was born quite small and is still small now as a preschooler! Like in the womb, he has a normal sized body and head but he does have little legs. Not sure if this will change as he gets older but oh my goodness he’s soo lovely and when I look back I just wish I hadn’t spent so many weeks of my pregnancy worrying 😌

Hi, I’m sorry that you are having this stress during your pregnancy. I must admit I have not read the whole thread, but I had similar with my daughter. Femurs on the 4th (and abdomen on the 96th), it did worry me a bit but my I gave birth to a lovely and perfectly proportioned little girl. I have similar in my currently pregnancy, femurs on the 5th, but not worried at all this time! I think sometimes they tell us too much. Please do try not to worry 🫶

Hello

thank you for your message, I am not sure if our hospital is research one, she just said with his femurs and my age she has to offer the amnio, I have booked the NIPT for Wednesday and I’m just praying to everything he’s ok. I’m glad things worked out fine for you.

Thank you for this it’s really helpful. X

Thank you all ♥️

Hoping the NIPT is ok and I can finally relax the last couple weeks have been so so horrendous.

Fingers xed

Ah OP sending lots of love, I’m glad you’ve managed to book a NIPT. Sending lots crossed fingers your way xxx

Has anyone else had the NIPT? How long did your results take? She said to me 5-7 working days 😳 she scanned him during my appointment and said his femurs are shorter but within (their) normal range. Praying all is ok.

I had NIPT and it took six working days to get my results. I had to chase them too. I wish you the best of luck with your results.

I have heard that femur measurements are often small relative to the other measurements as they’re calculated using an outdated method. I’m not sure of the mathematical details but basically; if you have a small measurement, it’ll be the femurs. My boy has small femurs on his scans. NIPT was fine though.

I hope all is well x

Thank you that’s really encouraging 😊

I had NIPT. It came back in 3-4 days. I’ve done it at Fetal Medicine Center in London. I had Amnio there as well.

This had to be private apparently I don’t qualify for it done on nhs.