First-trimester prenatal programs that screen for fetal aneuploidy'may incidentally identiy pregnancies at risk for fetalgrowth restriction unrelated to karyotype. In their analysis of 8012 women, the risk for growth restriction was higher in eukaryotic fetuses with extremely low free 3-human chorionic gonadotropin (3-hCG) and pregnancy-associated plasma protein-A (PAPP-A) levels (Krantz, 2004). From her review, Dugof (2010) concluded that a low PAPP-A level is strongly associated with poor fetal growth, but studies of free 3-hCG are conflicting.
Second-trimester analytes, including elevated alpha-fetoprotein and inhibin A levels and low unconjugated serum estriol concentrations, are significantly associated with birthweight below the 5th percentile. An even greater risk of poor growth is linked with certain combinations of these analytes. Still, these markers are poor screening tools for complications such as fetalgrowth restriction due to low sensitivity and positive-predictive values (Dugof, 2010). Nuchal translucency is also not predictive of fetal-growth restriction. he role of all these markers in aneuploidy screening is discussed in Chapter 14 (p. 281).
Identification of the inappropriately growing fetus remains a challenge. Eary establishment of gestational age, ascertainment of maternal weight gain, and careful measurement of uterine fundal growth throughout pregnancy will identiy many cases of abnormal fetal growth in low-risk women. Risk factors, including aprior growth-restricted etus, raise the recurrence risk to nearly 20 percent (American College of Obstetricians and Gynecologists, 2015). In women with risk factors, serial sonographic evaluation is considered. Although examination frequency varies depending on indications, an initial early dating examination followed by an examination at 32 to 34 weeks, or when otherwise clinically indicated, will identiy many growthrestricted fetuses. Even so, deinitive diagnosis frequently cannot be made until delivery.
According to one systematic review, insuicient evidence supports the utility of fundal height measurement to detect fetalgrowth restriction (Robert Peter, 2015). Nonetheless, carefully performed serial fundal height measurements are recommended as a simple, safe, inexpensive, and reasonably accurate screening method to detect growth-restricted fetuses. As a screening tool, its principal drawback is imprecision. Haragan and coworkers (2015) reported sensitivities of 71 and 43 percent for detecting excessive or deficient fetal growth. Specificities were 85 and 66 percent, respectively.
he method used by most for fundal height measurement is described in Chapter 9 (p. 164). Between 18 and 30 weeks' gestation, the uterine fundal height in centimeters coincides within 2 weeks of gestational age. Thus, if the measurement is more than 2 to 3 cm from the expected height, inappropriate fetal growth is suspected and sonography is considered.
One supporting point for routine sonographic evaluation of all pregnancies is the opportunity to diagnose growth restriction. Typically, such routine screening incorporates an early initial sonographic examination-usually at 16 to 20 weeks' gestation. Increasingly, a first-trimester examination is added to establish gestational age and identiy anomalies. Some then recommend repeat sonographic evaluation at 32 to 34 weeks to evaluate fetal growth.
First-trimester sonography has limited accuracy to predict SGA newborns. For example, Croverro and associates (2017) reported detection rates of 35 and 42 percent with false-positive rates of 5 and 10 percent, respectively. From nearly 9000 screened pregnancies, Tuuli and colleagues (2011) concluded