Ultrasound signs of fetal development delay
Last reviewed: 19.10.2021
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It is necessary to differentiate the symmetrical and asymmetric retardation of fetal development, since they have different genesis, a different prognosis, and, accordingly, the tactics of patients management.
- Symmetrical retardation of intrauterine development - low rates of fetal development. In such a fetus (symmetrical), developmental delay can be caused by chromosomal abnormalities, infectious diseases or maternal malnutrition, appears exclusively in the early stages of pregnancy. The ratio of the size of the head and trunk is within the normal range, with the fetus evenly smaller than the expected gestational age: all sizes are proportionally reduced.
- Asymmetric retardation of intrauterine development of the fetus is a delay in development in the late stages. With late (asymmetric) growth retardation of the fetus, damage occurs in the late stages of development (after 32 weeks), when the most pronounced accumulation of fat in the fetus occurs. The abdominal circumference will be significantly less than the normal values, the ratio of the head size to the size of the trunk will also be changed. Such a delay in development occurs when the placental circulation is poor in mothers with pre-eclampsia, edema, proteinuria, hypertension. The prognosis of pregnancy will depend on the adequacy of treatment for the mother.
Symmetrical retardation of intrauterine fetal development:
- The ratio of the size of the head to the size of the trunk of the fetus is normal.
- It begins in the early stages of pregnancy.
- All dimensions are reduced proportionally.
Asymmetric retardation of intrauterine fetal development:
- The ratio of the size of the head to the size of the trunk of the fetus is abnormal.
- It begins in the late stages of pregnancy.
- The values of the circumference of the abdomen are much lower than normal.
Ultrasound does not always accurately identify the intrauterine growth retardation of the fetus. Clinical and laboratory data should complement the study.
Measurements necessary for determining fetal development
A complete list of measurements necessary for the diagnosis of intrauterine growth retardation includes:
- measurement of biparietal diameter;
- measurement of the circumference of the fetal head;
- measuring the circumference of the abdomen;
- measuring the length of the fetus.
How is the gestational age determined by ultrasound?
Comparison of the size of the fetus with the duration of pregnancy can be important for the diagnosis of intrauterine growth retardation. During the first routine examination, determine the gestation period according to the coccygeal-parietal size, the size of the head and the length of the thigh. In subsequent studies, determine the expected duration of pregnancy, adding weeks that have elapsed since the first study to the time determined by the first ultrasound study.
In the initial ultrasound study, the determination of the gestation period is made on the basis of measurements of the coccygeal-parietal size or measurements of the head or femur length.
In subsequent studies, the due gestation period is defined as the sum of the weeks of gestation determined at the first study and the number of weeks elapsed since the first study.
Is it possible to use the dimensions of the fetal head as parameters of fetal development?
Dimensions of the head (both the biparietal diameter and the length of the head circumference) should correspond to the established term of pregnancy, i.e. The size of the head should fit within the interval established for the given period of pregnancy.
In this case, if one biparietal size is used, about 60% of cases of intrauterine growth retardation will be detected. When used as a criterion for diagnosing the value of the abdominal circumference, as well as other measurements, the sensitivity increases to 70-80%.
Tables used to determine gestational age, fetal body weight or development parameters should be acceptable for this particular social group.
Can I use the dimensions of the abdomen as parameters for the development of the fetus?
Measure the abdomen and determine the appropriate percentile for the proper term of pregnancy. The length of the circumference of the abdomen with a value less than the 5th percentile is a sign of the presence of an intrauterine delay in the development of the fetus.
What is the mass of the fetus? From what percentile the body weight is considered reduced in comparison with normal?
Determine the body weight of the fetus from the biometric tables using at least two parameters, and compare the fetal body weight with the standard values for the due gestation period. With a decrease in the fetal body weight below the 10th percentile, there is an intrauterine growth retardation of the fetus. Pathologically low body weight usually occurs at abnormally low values of the circumference of the abdomen and the head-trunk ratio.
Is the head-torso relationship normal, elevated or low?
The head-trunk relation is defined as the ratio of the head circumference to the abdominal circumference. It must be remembered that developmental defects can change the length of the circumference of the head or abdomen. The ratio is considered normal if its value is within the 5-95th percentile from the proper average for the established term of pregnancy.
Head-Torso ratio = Head circumference / Abdominal circumference
The head-trunk relationship determines whether there is a delay in the fetal development of the fetus symmetrical or asymmetric. If the fetus is small, and the ratio is normal, then the development delay is symmetrical. If the abdominal circumference or body weight of the fetus is reduced, and the head-trunk ratio is increased (by more than the 95th percentile), there is an asymmetric retardation of fetal development.
Asymmetric developmental delay is easier to diagnose than symmetrical.
If suspected intrauterine growth retardation of the fetus, several measurements must be made to determine the rate of fetal development with an interval of at least 2 or even 3 hours.
Do not need to conduct the study at intervals of 1 week. Changes can be insignificant for accurate registration.
There are limitations in the accuracy of the ultrasound method. Use the entire set of clinical and laboratory data, as well as dynamic ultrasound data (with an interval of at least 2 weeks) in assessing the development of the fetus.