Intrauterine Growth Retardation Recognition

The differentiation between symmetrical and asymmetrical growth retardation is important because they have different causes and different prognoses, and require different management.

1. Symmetrical growth retardation-low-profile fetus. 

In the low-profile fetus, (symmetrical) growth retardation is caused by a chromosomal abnormality, infection, or maternal malnutrition, and becomes apparent earlier in gestation. The head: body ratio remains within normal limits and the fetus is symmetrically retarded: all the measurements are reduced in the same proportion.

2. Asymmetrical growth retardation-late growth deceleration. 

In late (asymmetrical) growth retardation, the fetal insults occur later in gestation (after the 32nd week) when fat accumulation should be greatest. The abdominal circumference will be significantly lower than normal and the head: body ratio will also be abnormal. Such growth retardation results from placental insufficiency in mothers with pre-eclampsia, edema, proteinuria, and hypertension. The prognosis for the fetus will be improved by adequate maternal treatment.

Symmetrical growth retardation:

• Head:body ratio is normal.

• Starts in early pregnancy.

• All measurements reduced equally.

Asymmetrical growth retardation:

• Head:body ratio is abnormal.

• Starts in late pregnancy.

• Abdominal circumference is less than normal.

Ultrasound cannot always accurately diagnose intrauterine growth retardation.

Clinical and laboratory findings must be included in the measurement

Measurements to assess mental growth 

A complete evaluation of the fetal growth wall requires measurements of:

• the biparietal diameter (BPD);
• the head circumference;
• the abdominal circumference;
• the length of the femur.

What is the Ultrasound-determined gestational age?

Comparison of fetal size and gestational age can be proved a valuable indicator of intrauterine growth retardation. During the first routine scan, define the ultrasound gestational age based on the crown-rump length, head measurement, and femur length. For follow-up studies, calculate age as the initial age (however derived) plus the number of weeks intervening.

At first scan, estimated gestational age is based either on crown-rump length, or on head of femur measurement.

At follow-up studies, gestational age is taken as the estimated age at the initial study plus the number of weeks intervening.

Is the Head Size Appropriate 

The head size (either biparietal diameter or head circumference) should be appropriate for the estimated ultrasound gestational age, i.e. the head measurement should fall within the range for estimated gestational age.

Using the biparietal diameter alone, about 60% of growth-retareded fetuses will be detected. Using the abdominal circumference as well as other measurements, the sensitivity increases 70-80%.

Tables used to estimate gestational age, fatal weight or development must be appropriate for the social group of the patient.

 Is the abdominal size appropriate?

Measures the abdominal and determines the appropriate percentile. An abdominal circumference less than the 5th percentile is abdominal and suggests intrauterine growth retardation.

What is the fetal weight? In what percentile does the weight fall?

Determine the fetal weight from biometric tables using at least two parameters and compare it with the standard distribution for the estimated gestational age. Intrauterine growth is considered to be retarded when the weight is lower than the 10th percentile. An abnormally low weight of the fetus is usually observed after the abdominal circumference and head: body ratio has become abnormal.

Is the head: body ratio normal, elevated, or low?

The head: body ratio is calculated by dividing the head circumference. It should be remembered that malformations may change the size of the head or abdomen. With normal anatomy, the head: body ratio can be considered normal if it lies between the 5th and 95th percentiles for the gestational age.

The head-body ratio determines whether the growth retardation is symmetrical or asymmetrical. If the fetus is small and the ratio is normal, the fetus is symmetrically growth retarded, if the abdominal circumference or weight is low and the ratio is evaluated (greater than the 95th percentile), there is asymmetrical growth retardation.

Asymmetrical growth retardation is easier to diagnose symmetrical growth retardaion.