Explanation of some terms in the four-dimensional ultrasound on the 26th day of pregnancy

There are many examination items in the four-dimensional color ultrasound, generally including femur length, humerus length, head circumference, etc. The specific explanations are very effective in checking the child's physical development. According to the characteristics of a normal 26-week fetus, the child's growth and development can be discovered, and the child's fetal malformation examination can be performed, as well as the child's condition can be judged based on the development of various body functions such as weight.

Biparietal diameter (BPD): The longest part of the head from left to right, also called the greatest transverse diameter of the fetal head, is measured from left to right. Based on this, the weight and developmental status of the fetus can be estimated, and it can be determined whether there is cephalopelvic asymmetry and whether a smooth delivery can be achieved.

Occipital-frontal diameter (OFD): The distance from the root of the fetal nose to the occipital protuberance, also known as the anterior-posterior diameter, is also the longest part of the fetal head from front to back. This data is used to determine the fetal development and gestational age.

Femur length (FL): The length of the thigh, also called femur length, which is the longest part of the body. Used together with BPD (largest transverse diameter of the fetal head) to estimate fetal weight.

Humerus length (HL): the length of the fetal upper arm bone, humerus length = -5.4282 + 0.7542 × biparietal diameter.

Head circumference (HC): The length around the head, also called the fetal head circumference, is the numerical value of the length of the head. Used to confirm the developmental status of the fetus.

Abdominal circumference (AC): The length of the abdomen, also called abdominal circumference, is the length of the fetal abdomen. Used together with APTD (anteroposterior trunk diameter) and TTD (transverse trunk diameter) to infer fetal development.

Umbilical cord blood flow ratio (A/B): refers to the blood flow in the umbilical cord. The umbilical cord is the only channel for gas exchange, nutrient supply and metabolic product elimination between the mother and the fetus. Its hemodynamic changes can reflect certain pathological changes in the placenta, fetus, and even the mother, as well as certain high-risk pregnancy factors. The umbilical artery resistance index (RI) and the ratio of the maximum systolic blood flow velocity to the maximum end-diastolic blood flow velocity (S/D) are two hemodynamic indicators representing the umbilical artery and are often used to detect the blood circulation and function of the placenta. In normal pregnancy, as the gestational age increases, the fetal needs increase and the S/D and RI values ​​decrease.

Position of the fetus (LOA): It is a way of positioning the fetal head, representing left occipital anterior position.

Amniotic fluid index: refers to the value obtained by adding the depth of amniotic fluid in 4 areas (upper, lower, left and right) centered on the navel of the pregnant woman during B-ultrasound examination.

Amniotic fluid dark area: Under normal circumstances, the amniotic fluid area observed in B-ultrasound is low-density, so the maximum depth of the amniotic fluid dark area is used clinically to indicate the deepest amount of amniotic fluid, which is normally 3 to 8 cm.

A four-dimensional color ultrasound can reveal a lot of things. Generally, it is sufficient to do a four-dimensional color ultrasound at an appropriate time, and the best time is usually between 22 and 28 weeks. It can quickly observe the child's health, and can also observe the child's appearance, movements, activities and even breathing.