Length of the Fetus

Knowing the length of the fetus during the various stages of pregnancy allows to evaluate its gestational age, growth and state of health, highlighting any morphological anomalies.

Obstetric ultrasound

The obstetric ultrasound, performed within the first trimester of pregnancy, has the task of investigating the number of fetuses, their viability and the gestational period. In this first phase, in fact, the cranio - caudal length (head - sacrum) appears almost constant in fetuses of identical dating.

Therefore, by detecting this parameter through ultrasound images, the doctor can establish the gestational age and the expected date of delivery, all with an excellent degree of approximation. If measured between the 7th and 11th week, for example, the skull length. caudal (CRL), has an accuracy of more or less 3/4 days in 95% of cases.

The ultrasound gestational period calculated in this way may vary slightly with respect to that established on the basis of the last menstruation (amnesthetic period).

For the same purpose and with the same modalities, the biparietal diameter (BPD) can be detected during early ultrasound, which when measured between the 12th and 16th week, offers an accuracy similar to the cranio-caudal length (plus or minus 3 / 4 days in 95% of cases).

Morphological ultrasound

After the first trimester of pregnancy, the chances of recognizing malformative pathologies of the fetus increase significantly. Therefore, around the twentieth week of pregnancy, a second ultrasound is performed, called morphological, which also has the task of evaluating a whole series of biometric parameters. For example, the reduction of the length of the humerus or of the femur compared to the reference values, is frequently observed in trisomy 21 (Down syndrome). ), it is also important to establish or confirm the gestational age of the baby.

Biometric ultrasound

In the third trimester of pregnancy (between the 28th and 32nd week) the so-called obstetric or biometric ultrasound is performed, which again investigates the growth and the fetal anatomy, allowing to detect any malformations escaped from the previous morphological ultrasound. This ultrasound examination is never performed. used to date pregnancy, a parameter that must have already been clearly established in previous ultrasound investigations. Rather, biometric ultrasound evaluates the adequacy of fetal growth on the basis of standard values, referred to the gestational age estimated in previous checks; among the parameters detected, we recall the aforementioned BPD (biparietal diameter), the length of the femur ( LF), head circumference (CC) and abdominal circumference (CA).

Calculation of gestational age

Below are some calculation modules to establish the gestational age in relation to specific fetal biometric parameters. The results should not replace the opinion and advice of the health personnel responsible for evaluating the health of the fetus.

BIPARIETAL DIAMETER (BPD)

Length in mm: Gestational age weeks

CRANIAL CIRCUMFERENCE (HC)

Head circumference in mm: Gestational age = weeks

ABDOMINAL CIRCUMFERENCE (AC)

Abdominal circumference in mm: Gestational age = weeks

FEMUR LENGTH (FL)

Length in mm: Gestational age = weeks