Ultrasound signs of fetal retardation

It is necessary to differentiate symmetrical and asymmetrical fetal growth retardation, since they have different genesis, different prognosis, and accordingly, the tactics of patient management change.

• Symmetrical intrauterine growth retardation - low fetal development indicators. In such a fetus (symmetrical) developmental delay can be caused by chromosomal abnormalities, infectious diseases or nutritional deficiency in the mother, appears exclusively in the early stages of pregnancy. The ratio of the head and body sizes is within the normal range, while the fetus is uniformly smaller than the expected gestational age: all sizes are proportionally reduced.
• Asymmetric intrauterine growth retardation of the fetus is a delay in development at late stages. In late (asymmetric) fetal growth retardation, damage occurs at late stages of development (after 32 weeks), when the fetus has the most pronounced accumulation of fat. The abdominal circumference will be significantly smaller than normal, and the ratio of the head to the body size will also be changed. Such a delay in development occurs with insufficient placental circulation in mothers with preeclampsia, edema, proteinuria, and hypertension. The prognosis for pregnancy will depend on the adequacy of the mother's treatment.

Symmetrical intrauterine growth retardation:

• The ratio of the head size to the body size of the fetus is normal.
• It begins in the early stages of pregnancy.
• All dimensions have been reduced proportionally.

Asymmetric intrauterine growth retardation:

• The ratio of the fetal head size to the body size is abnormal.
• It begins in the late stages of pregnancy.
• The abdominal circumference values are significantly less than normal.

Ultrasound does not always accurately detect intrauterine growth restriction. Clinical and laboratory data should complement the examination.

Measurements needed to determine fetal development

The complete list of measurements required to diagnose intrauterine growth restriction includes:

• measurement of biparietal diameter;
• measurement of fetal head circumference;
• measurement of abdominal circumference;
• Measuring the length of the fetus.

How is gestational age determined by ultrasound?

Comparison of fetal size with gestational age may be important in diagnosing intrauterine growth restriction. During the first routine examination, determine gestational age by measuring crown-rump length, head size, and femur length. During subsequent examinations, determine the estimated gestational age by adding the weeks since the first examination to the age determined during the first ultrasound examination.

During the initial ultrasound examination, the gestational age is determined based on measurements of the crown-rump length or measurements of the fetal head or femur length.

In subsequent studies, the due gestational age is determined as the sum of the weeks of pregnancy determined in the first study and the number of weeks that have passed since the first study.

Can fetal head size be used as a parameter for fetal development?

The dimensions of the head (both the biparietal diameter and the head circumference) must correspond to the established gestational age, i.e. the dimensions of the head must fit within the interval established for the given gestational age.

In this case, if one biparietal size is used, about 60% of cases of intrauterine growth retardation of the fetus will be detected. When using the abdominal circumference value as a diagnostic criterion, as well as other measurements, the sensitivity increases to 70-80%.

Tables used to determine gestational age, fetal weight, or growth parameters must be appropriate for the particular social group.

Can abdominal dimensions be used as parameters of fetal development?

Measure your abdomen and determine the percentile corresponding to the due date of pregnancy. An abdominal circumference less than the 5th percentile is a sign of intrauterine growth retardation.

What is fetal body weight? At what percentile is body weight considered to be underweight compared to normal?

Determine the fetal weight using biometric tables, using at least two parameters, and compare the fetal weight with standard values for the appropriate gestational age. If the fetal weight decreases below the 10th percentile, there is intrauterine growth retardation. Abnormally low birth weight usually occurs with abnormally low values of the abdominal circumference and head-to-body ratio.

Is the head-body ratio normal, high, or low?

The head-to-body ratio is defined as the ratio of the head circumference to the abdominal circumference. It is important to remember that malformations can change the length of the head or abdominal circumference. The ratio is considered normal if its value is within the 5th to 95th percentile of the expected average for the established gestational age.

Head to torso ratio = Head circumference / Abdominal circumference

The head-to-body ratio determines whether the intrauterine growth restriction is symmetrical or asymmetrical. If the fetus is small and the ratio is normal, the growth restriction is symmetrical. If the abdominal circumference or fetal weight is decreased and the head-to-body ratio is increased (more than the 95th percentile), the intrauterine growth restriction is asymmetrical.

Asymmetrical developmental delay is easier to diagnose than symmetrical delay.

If intrauterine growth restriction is suspected, several measurements should be taken to determine the rate of fetal growth at intervals of at least 2 or even 3 weeks.

There is no need to conduct studies at intervals of 1 week. Changes may be too small to be accurately recorded.

There are limitations to the accuracy of the ultrasound method. Use the entire set of clinical and laboratory data, as well as data from dynamic ultrasound measurements (at intervals of at least 2 weeks) when assessing fetal development.