Femoral bone is several weeks shorter and diagnosed as deformity

After pregnancy, everyone needs to do B-ultrasound frequently. If they don't do it, they will feel uneasy, and if they do it too much, they will be worried. When doing major malformation screening, if no obvious fetal structural abnormalities are found, it can be considered a relief, but there will still be concerns. In the middle and late stages of pregnancy, the most common concerns are "headaches", "short legs", "aging placenta", and "umbilical cord around the fetus' neck". Today I’m going to talk to you about “short legs”. The so-called "short legs" refers to the short femoral head of the fetus, which is not uncommon. The incidence rate is about 0.5%-5% in the entire population. The incidence rate depends on many factors, and the diagnostic criteria and the doctor's operational errors are also related. Generally speaking, the incidence rate of short femoral head in fetuses is slightly higher in the Asian population.

There is no consensus on the diagnostic criteria for short femoral head. The most common criteria are femoral head length less than the 5th percentile for babies of the same gestational age or less than 2 standard deviations for babies of the same gestational age. Common causes of short femoral head in fetuses include: physiological short femoral head, fetal growth restriction (FGR), congenital skeletal dysplasia, chromosomal abnormalities or gene mutations, among which the most common is physiological short femoral head. In other words, except for slightly shorter legs, everything else is normal.

Femoral head shortening can be divided into "independent femoral head shortening" and "dependent femoral head shortening".

"Independent femoral head shortness"

It means that the color Doppler ultrasound examination only found that the fetus's femoral head was short and symmetrical, and there were no other abnormalities in the fetus. In this case, the prognosis of the fetus is mostly good, but the incidence of FGR, premature birth, low birth weight, and neonatal ICU admission is slightly increased.

In addition, the short femoral head of the fetus itself is an "ultrasound soft marker" of chromosomal abnormality, and the risk of chromosomal abnormality should still be considered, but compared with NT (neck translucency), its risk value is relatively small. If the risk value of previous Down syndrome screening or minimally invasive fetal DNA testing is relatively low, further testing can be ignored; if the Down syndrome screening is medium risk, sufficient communication with the patient and relatives is needed to decide whether further testing is needed; if it is high risk, amniocentesis is recommended. The standard of treatment is to determine the gestational age based on the history of amenorrhea and color Doppler ultrasound examination during early pregnancy, conduct regular follow-up visits and tests to eliminate the possibility of FGR and chromosomal abnormalities, and generally no specific treatment is required.

"Non-independent femoral head shortening"

It means that color ultrasound examination reveals that the fetus has a short femoral head, and there are other fetal abnormalities. These fetal abnormalities can be divided into two categories: one is the abnormality of the whole skeletal system, which includes bowing, fracture, and unequal ossification of long bones. These abnormalities can be further divided into mortal femoral head dysplasia and non-mortal femoral head dysplasia. After the child is born, he will have dwarfism. In this case, sufficient communication with the patient and relatives is needed, and amniocentesis and genetic testing are recommended. If it is hereditary skeletal dysplasia, termination of pregnancy can be considered.

Another type of fetal abnormality is the so-called fetal "ultrasound soft markers", which are not major fetal structural abnormalities, but just some small structural "genetic mutations", which will not affect the fetus in function, but often cause an increased risk of fetal chromosome quantity abnormalities and structural abnormalities. Common "ultrasound soft markers" include fetal NT (nuchal translucency) thickening, ventriculomegaly, increased intestinal echoes, atrial bright spots, renal pelvic dilatation, choroidal cysts, etc. These "ultrasound soft markers" indicate that the fetus has an increased risk of trisomy 21, trisomy 18, trisomy 13, X monosomy, mosaic sex chromosomes, and partial absence and mutation of some sex chromosomes. It is necessary to communicate adequately with the patient and relatives, and amniocentesis is recommended to rule out the possibility of chromosomal abnormalities.