Hello,
Thanks for posting your query.
Please do not worry.
Yes I agree that a 39 year old primipara ( first pregnancy )is considered to be having a high risk pregnancy but if her chromosome studies and previous anomaly scans have been normal then it's not very worrisome .
Femur length measurements are used as an intrauterine growth indicator and a short Femur length less than 3-5th percentile can occur due to significant causes such as skeletal dysplasias or Intrauterine growth retardation (iugr).
However such measurements are subjective approximations and can be erroneous too depending on the technician and the machine . Also many familial or constitutional short stature babies can be absolutely normal yet have short femur lengths .
So just based on one abnormal scan one cannot confirm the diagnosis . Rather her obstetrician would look at her clinical history , examination findings and previous records and if necessary successive repeat scans to come to a conclusion and confirm the finding .

In short , a short femur length could be present in normal or abnormal fetuses ( like skeletal dysplasias or iugr babies and in your daughters case it's more likely to be normal if all her previous reports have been normal ,but nothing can be conclusively said without a thorough reevaluation by her obstetrician .
So kindly discuss it with her doctor .
Even in cases of growth retardation treatment can be started in mother to improve the blood flow and growth of the fetus .
Only in case of genetic problems like skeletal dysplasias or syndromes not much can be done at present and the child has to be evaluated after birth.
So I would advise your daughter to have a positive outlook and avoid any stress as it can further hamper the growth of the baby.
Hope I have answered your query.
Kindly accept my answer if you have no further queries.
Wishing you good health.
Regards

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