How is fetal head circumference normal, what is abnormal?

Head circumference is one of the important indicators that the fetus is developing normally. However, how is the indicator abnormal and what should the pregnant mother do in this case?

The index of head circumference over the gestational weeks of mothers needs to know

Head circumference is one of the most common indicators of the fetus that is shown on fetal ultrasound results with the abbreviation HC, which stands for Head circumference.

Depending on the pregnancy weeks, the doctor will review the head circumference index as well as other indicators of the fetus to check the normal development of the baby. Detail:

From week 1 to week 4, the fetus is just a very small embryo. The fetal index from 4-7 weeks of mothers should note the length of the buttock and the diameter of the pregnancy bag.

In the 6th week of pregnancy, the diameter of the pregnancy bag can be about 14-25mm.

From 7 weeks of pregnancy, the ultrasound will show the length of the buttocks of the baby.

From 12 weeks onwards, it is possible to determine fetal head circumference, bipolar diameter as well as femur length.

Each fetus has different metrics, for example having a larger head circumference or a shorter thighbone. Often these differences are more or less inherited from the parents.

If the difference is insignificant, within the permissible limits, these indicators are considered to be no abnormality.

Table of indicators for pediatric head circumference and indicators for pregnant mothers 

Is fetal head circumference small, not up to standards?

This is a worry of many mothers when it comes to antenatal care. Is my baby developing normally? What do indicators such as fetal head circumference tell, especially when they are smaller than normal standards?

According to the doctors, if concluding that the baby's head circumference is small, this is quite a concern. The causes of this condition are difficult to determine, but the most common ones are:

Genetics: small head family

The fetus develops slowly

Genetic abnormalities.

Chromosome abnormalities

Fetal infection

Central nervous system abnormalities

Single ventricle (Holoprosencephaly)

Lissencephaly (Lissencephaly)

Split brain

Agenesis of the corpus callosum

Cranial joint closure early

Endocrine system abnormalities (hypothyroidism, pituitary failure, ...)

What should pregnant mothers do if the baby's head circumference is abnormally small?

First, you need to consult with your antenatal doctor to get directions to perform the necessary tests to find out the exact cause and treatment for the fetus in this condition.

Usually, doctors will perform the following steps:

MRI scan

MRI, also called magnetic resonance imaging (MRI), is a means of providing detailed pictures of the inside of the body. From there, the doctor can detect abnormal structures of the organs and recommend appropriate treatment.

In obstetrics, an MRI of the fetus will provide more information about the baby, in addition to an ultrasound tool, especially in risky pregnancies.

If your baby is at risk for small head circumference then this is one of the ways to closely examine brain structures.

Amniocentesis

This is a procedure that uses a needle to drain amniotic fluid. This sample is checked for infection or chromosomal abnormalities. However, this is a last resort, as this invasive method can lead to the risk of preterm birth.

In case the test result is normal, the pregnant mother should take care of the pregnancy, increase the nutrition, and monitor the fetal development.

However, it is necessary to understand that many cases of normal chromosomal amniocentesis are still present, but there are still some very small genetic mutations that are currently not available in Vietnamese medical conditions. Therefore, pregnant mothers need to continue to refer to treatment directions from an obstetrician.

See more: 

Fetus index according to each week the most standard and guide pregnant mother to read fetal ultrasound results

Calculation and factors affecting pregnant belly circumference

How is fetal nose bone length normal?