Low birthweight (LBW) refers to infants with an absolute birth weight <2500 g regardless of gestational age.
Small-for-gestational-age (SGA) fetuses are <10th percentile for gestational age. Fetuses >90th percentile are termed “large for gestational age” (LGA). Fetuses between the 10th and 90th percentiles are referred to as “appropriate for gestational age” (AGA). Correct assignment of fetal weight category is dependent on accurate dating of the pregnancy because birthweight is a function of both gestational age and rate of fetal growth.
Intrauterine growth restriction
Definition. Intrauterine growth restriction (IUGR) refers to any fetus that fails to reach its full growth potential.
Incidence. Of fetuses 4–8% are diagnosed with IUGR.
Classification. IUGR can be classified as symmetric (in which the fetus is proportionally small, suggesting long-term compromise) or asymmetric (in which the fetal head is proportionally larger than the body, suggesting short-term compromise with “sparing” of the brain). This distinction is, however, of little clinical value.
Causes. IUGR represents the clinical end-point of many different fetal, uteroplacental, and maternal conditions. An attempt should be made to determine the cause before delivery in order to provide counseling, perform ultrasonographic evaluation for fetal growth and delineation of anatomy, and obtain neonatal consultation. Frequently, the cause is readily apparent (Figure 51.1).
Risk factors. Numerous pre-existing and acquired conditions predispose the fetus to IUGR (Figure 51.2).
Diagnosis. The clinical diagnosis of IUGR is unreliable, but a fundal height measurement significantly less than expected (3–4 cm) for gestational age may suggest the diagnosis. IUGR is confirmed by sonographic measurements (Figure 51.3).
Pathophysiology. IUGR most commonly results from compromise of uteroplacental blood flow (Figure 51.4).
Prevention.
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