Can a short femur length in sonography indicate the baby has trisomy 21?

Question

Hello doctor,

My wife is currently pregnant and in her 21st week. We did an organ screening, and in sonography, everything was normal. But a question is being raised that the baby's femur is short (28.02 mm). Because of this, they are saying this could be a reason for Trisomy 21. We both generally are small in height, my wife is 145 cm, and I am 165 cm. We do not want to do the chromosomal test because this might be risky. Based on the femur length of 28.02 mm, the software calculates it out of the range. Could you please help? Could you please check if this is normal? We believe our baby is healthy.

Answer 1

Hello,

Welcome to icliniq.com.

I read your query and can understand your concern.

A short femur length finding on ultrasound may indicate the need for further testing to rule out certain conditions, such as intrauterine growth restriction, Down syndrome, or other chromosomal issues. However, often the baby is perfectly healthy. Femur length is among many variables that should be used to determine a baby's health. It is important to know that in most of these pregnancies (73%), parents will go on to have a full-term delivery of a healthy baby whose size is appropriate for gestational age.

It can be not very comforting to hear that your baby has a short femur length or another marker of concern. However, in most cases, the outcome is still a healthy, full-term baby. If your doctor finds that your baby has a shorter-than-expected femur length, further testing may help to understand what this measurement means and how best to care for your baby during pregnancy, at birth, and beyond.

Your doctor is the best person to decide what's best. Perhaps you could get screening tests first, and though they do not provide a definitive diagnosis, they are safer for the mother and the developing baby. Screening tests often include a combination of a blood test, which measures the number of various substances in the mother's blood, such as MS-AFP (maternal serum alpha-fetoprotein), Triple Screen, and Quad-screen, and an ultrasound, which creates a picture of the baby. The doctor can decide if she needs further diagnostic tests if that shows a gross abnormality.

As I said, the baby may be perfectly healthy.

Hope this helps.

Thanks and take care.