What is the crown-rump length of the fetus?

Pregnant women need to undergo various examinations during pregnancy. Through prenatal examinations, they can better understand the development of the fetus and learn about some problems that may or already exist in the fetus. The crown-rump length of the fetus, also known as the crown-rump diameter, refers to the distance from the top of the skull to the outer side of the buttocks. There are certain standards for the crown-rump length of the fetus. Here we will introduce you to the relevant knowledge about the crown-rump length of the fetus in detail!

1. What is crown-hip length?

The crown-rump diameter, also known as the crown-rump length (CRL), refers to the distance from the top of the fetus's skull to the outer edge of the buttocks, and is usually measured around 7-12 weeks of pregnancy.

2. Estimation Method

When performing ultrasound examination of an early-pregnancy fetus, the crown-rump diameter is often used to estimate the fetal gestational age, which is the most accurate estimation method. At the beginning of the 6th week, the embryo is too small to be measured accurately. As the gestational age increases, the embryo grows and its morphological curve becomes C-shaped, with a relatively large head end that is easy to identify. Therefore, the following formula was used to calculate gestational age.

Formula: Gestational age (weeks) = CRL (cm) + 6.5

Measuring standard sections: Take the longest and straightest midsagittal section image of the fetal body or trunk.

3. Notes

(1) Applicable to 7-12 weeks of pregnancy.

(2) Measure the longest diameter of the fetus (measure three times and take the average value).

(3) Fetal limbs and yolk sac are not included in the measurement.

4. Fetal crown-rump length standard comparison table

The standard for biparietal diameter of a 12-week fetus: The fetus grows to 4.58 cm, the external genitalia begin to develop, any deformities can be revealed, and the calcification of the skull becomes more complete. The skull halo is clear, the biparietal diameter can be measured, obvious deformities can be diagnosed, and the internal organs tend to become more complete afterwards.

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