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Fetal Growth Restriction

Growth restriction is defines as an infant born at or below the third percentile of mean weight for gestational age, with clinical evidence of dysfunctional or abnormal growth. The perinatal mortality rate of these infants is five times higher than that of normal infants. Approximately one half of growth-restricted babies show wasting of soft tissue and muscle mass, especially in the cheeks, arms, buttocks, and thighs. The skin is often dry.

Depending on the timing of growth restriction, as well as its etiology, infants can be either asymmetrically or symmetrically growth restricted. Asymmetric growth restriction generally occurs late in the second trimester or early in the third trimester of pregnancy. The fetal brain and heart are often spared because of non-reduced blood flow, and these fetuses usually demonstrate normal musculoskeletal growth.

Asymmetric growth restriction, which generally occurs during the phase of growth termed cellular hypertrophy, is attributed to placental insufficiency secondary to maternal hypertensive disorders, renal disease, heavy cigarette smoking, or diabetes with vascular disease. Factors associated with symmetrical growth restriction include chromosomal abnormalities (ie, trisomy 18 and 13) fetal growth restriction, intrauterine growth retardation, fetal growth restriction, developmental abnormalities secondary to teratogens (eg, anticonvulsants, narcotics, cocaine), and intrauterine fetal infections (eg, rubella, CMV, malaria, hepatitis A and B, toxoplasmosis, listeriosis, syphilis, tuberculosis).

The first clinical sign of fetal growth restriction may be an abnormally low increase in serial fundal height measurements. When fundal height growth is inappropriate for gestational age, an ultrasound examination should be ordered to confirm or refute the diagnosis. Most important is evaluation of the fetal head and abdominal circumferences and their ratio, as well as femur length. Abdominal circumference measurements are the most reliable index of fetal size.

Once fetal growth restriction is suspected, the fetus must be considered at risk for intrauterine hypoxia and possibly death. In those fetuses, near-term prompt delivery is indicated; however, in those remote from term, fetal surveillance is recommended. In general, fetal testing is performed twice a week by use of the NST, CST, BPP, or umbilical artery velocimetry. Amniotic fluid volume assessment should also be performed.