Femur length behind with 3 weeks!

[Mary9104]

How accurate have your late third trimester scans been? (36-38 weeks) Especially in regards to a shorter femur length? I just had a 38.5 week scan and the head and abdomen were at the 50th percentile while the femurs were in the 15th percentile (69mm) and measuring 3 weeks behind.. apparently the femurs should be close to 75 mm now. The femurs were of a normal size at my 30 week scan so I’m concerned regarding the drop.. The doctor did spend around 15 minutes trying to measure the femurs so I guess it wasn’t an easy task due to the babys size at this point… which makes me even more nervous as I’m not sure how accurate the measurement is.

I had exactly this at my 36 week scan. They didn't tell me a time scale they were behind but the femurs were just on the scale and all other measurements were between 50th-75th centile. I'm short though so the sonographer wasn't worried. He did have little legs when born but not noticeable to anyone else. They've caught up now at 18 months and are perfectly in proportion. I think he might have run out of room to grow in the womb.

Hi Op,

I always comment when I see this concern because it kind of ruined my pregnancy for me. I was scanned from 20 weeks every 4 weeks due to high fluid. However at every scan the femurs were always way behind everything else. The doctor never seem concerned but I went down a rabbit hole of constant google etc and convinced myself something wasn’t right especially seeing as I knew I was having a boy and my partner is 6’3. Anyway my baby was born 8.1 and is very long to the point that people comment how long he is and his grows are always too short on the legs 😂. Remember a foetus femur is so so tiny the margin for error is massive. Please please please don’t do what I did and become obsessed with this it’s really not worth it 😊

Hey hun I had this with my son now 5 bowels were bright had scans every week they said he would never walk loads of stuff worst pregnancy ever I ended up so stressed and sad! He’s 5 and running around his school. Try not to worry.

Thank you so much for all answers! I’m trying to stay positive and hoping all is well!

We had loads of growth scans and were told that the femur length was the least accurate measurement - it was often quite different from the other two.

My little boy is currently measuring just over 4 weeks behind and this means that he has completely dropped out of the chart for femur. Tummy and head are around 40-50th centile so overall he’s ~15th centile-this was at 33 weeks and I have another growth scan at 36 weeks. I think that they don’t worry unless baby drops under 10th centile and in my case the measurements for the femur have been consistently falling behind since 28 weeks when my first scan was. Placenta, blood flow and waters look okay.
Both my partner and DD have shorted legs and longer torso so my little boy is probably following the same trend, but I’m going to speak to my consultant after the 36 weeks scan and see what he thinks. Sometimes if there is iugr babies are better out and then in so if there are any concerns you will be offered an induction. In my case, I already have a c section booked for 39 weeks so if the growth has slowed down further I’ll see if changing the c section to 38 weeks is a possibility.
Good luck OP, as others have said in majority of the cases the out of range measurement is due to the shape and size of the femur.

@PurpleIsTheColour thank you for sharing! I hope everything will be well with your boy and good luck with the c-section!🙏

thank you! I’m sure it will be fine but can’t help worrying as the femurs were in the 60th percentile at my 30 week scan and is now falling behind, I’m hoping I can get a follow up regarding inducing at 40 weeks if the femurs continues to fall behind. so only a week to go and hopefully things will be alright until then.

Hi OP,

of course it’s your choice but i wouldn’t consider an induction based on femur length. It’s not dangerous and there are no other concerns that would indicate there is anything wrong. I was induced at 41+4 as my hind waters had broken but I hadn’t gone into labour naturally i had a horrific labour. I wouldn’t recommend induction unless absolutely needed.