How To Measure The Size Of A Baby In A Womb

How To Measure The Size Of A Baby In A WombThe most important aspect of prenatal careis measuring the size of the baby. The size of the baby is required to determine the age of the baby and identify certain problems.

When the size is determined the doctor can easily identify problems like intrauterine growth restriction.  Sometimes the baby becomes too large for gestational age and the doctors can be forced to induce delivery. However, there is no accurate system of measuring the size of the baby in the womb but still the doctors can use a number of methods to estimate the size of the fetus.

First Measurement

When the baby reaches between 7 to 14 weeks an ultrasound scan can be done to determine the length of the baby from the crown to the rump. At this stage the babies tuck their legs into the chest so the measurement is only possible in length from top of the head to the bottom. This is the best method adopted by the doctors as it gives an accurate estimate of the age of the baby.

Measurement In 5th Month

When the baby is 20 weeks, the fundal height needs to be measured. The fundal height refers to the length from the pubic bone to the top of the uterus. The doctor will now start feeling the uterus to understand how much it has grown.

Actually the fundal height (in cm) should be exactly same as the term of pregnancy (in weeks). It is disappointing to note that fundal height is not at all an accurate measurement. There is always an error in measurement due to the position of the baby and the amount of amniotic fluid.

Breech babies tend to be large than babies who have dropped into the womb of have turned sideways. Though this test does not reveal an accurate measurement, as discussed earlier, the method is still followed by doctors to get a rough estimate of the size of the baby. The doctor needs to ascertain that the baby is growing at the correct rate.

Measurement in The 7th Month

An ultrasound measurement of the femur length is done when the baby is nearing 26 weeks. During this period, the abdominal circumference and the distance between the two skull bones is also measured.

There are many doctors who take a lot of other measurements to be doubly sure. These are mainly the head circumference, humerus length and the measurement between the two bones in the fetal head.

There is a possibility of difference in the measurements but this difference should be investigated. It is best to avoid an average of all the measurements. That a baby has a flat head can be indicated by a small biparietal measurement.


No two babies grow at the same rate. From the 4th month the babies grow at varying rates prompting many medical experts to opine that the size of the baby is not an accurate indication of the age. The age can be correctly measured only in the first three months.

The bad news is there is no method present to correctly measure the size of the fetus. If the doctors use the abdominal circumference and the biparietal diameter as guides then there is a 10% chance of that result being erroneous.