Fetal growth restriction, previously called intrauterine growth restriction, is a condition in which a fetus does not achieve its optimal growth potential. It impacts up to 10% of pregnancies and has significant prenatal and postnatal consequences, including increased risk of perinatal death, neurodevelopmental abnormalities, metabolic syndrome, and cardiovascular disease.^1–4 For fetuses affected by growth restriction, adverse outcomes such as intraventricular hemorrhage, hypoxic ischemic encephalopathy, necrotizing enterocolitis, bronchopulmonary dysplasia, sepsis, and death are more common and severe when estimated fetal weight is below the third percentile, or the 10th percentile if uterine artery flow is abnormal.⁵

Definition

The term fetal growth restriction is recommended instead of intrauterine growth restriction.^1,2,6,7 Fetal growth restriction is a pathologic process and indicates distress preventing the fetus from achieving its ultimate growth potential. The American College of Obstetricians and Gynecologists (ACOG) defines a fetus with fetal growth restriction as having an estimated fetal weight below the 10th percentile for gestational age,¹ whereas the Society for Maternal-Fetal Medicine recommends an additional criterion of an abdominal circumference below the 10th percentile for gestational age.⁷ Severe fetal growth restriction is defined as estimated fetal weight below the third percentile.⁷ Population-based fetal growth references, such as the Hadlock formula, should be used to determine fetal weight percentiles instead of growth standards based on race and sex.⁷ Although the Hadlock formula was developed from a small, middle-class population in Texas that was almost exclusively White, it is more accurate at predicting adverse outcomes from fetal growth restriction than more diverse growth standards.^8–10

The term small for gestational age (SGA) applies to newborns whose measured birth weight is less than the 10th percentile for gestational age.¹ SGA newborns may have had fetal growth restriction, but may also be constitutionally small, physiologically normal, and have reached their growth potential. Some infants with normal birth weight who experienced growth restriction in utero are at risk of postnatal complications.

Etiology

Fetal, maternal, uteroplacental, and external factors can lead to fetal growth restriction through limited uteroplacental perfusion that limits fetal nutrition (Table 1).^1,11–14 Placentation and umbilical cord abnormalities are the most common causes of fetal growth restriction.¹ Factors associated with fetal growth restriction include multiple gestation, structural anomalies including congenital heart disease and gastroschisis, and genetic abnormalities including trisomies 13, 18, and 21.^11–13 Maternal nutrition, chronic diseases such as hypertensive disorders and pregestational diabetes mellitus, infections, and external factors such as drug or toxin exposure increase the risk of fetal growth restriction.^11–13 Although race and ethnicity are identified as risk factors, exposure to structural racism and socioeconomic inequality contributes to fetal growth restriction, not race or ethnicity themselves.¹⁴

Screening and Prevention

All pregnant patients should be screened for fetal growth restriction. A detailed medical and obstetric history should be obtained and risk factors, especially modifiable risk factors, should be identified (Table 1^1,11–14). Serial growth ultrasonography performed in pregnancies complicated by risk factors including chronic disease in the birthing parent, substance use, or a history of fetal growth restriction allows for earlier diagnosis.¹ In the absence of risk factors, fundal height measurements should be obtained at every obstetric visit after 24 weeks' gestation, preferably by the same clinician. If fundal height is more than 3 cm (1.2 in) below gestational age, formal ultrasonography is recommended. Body habitus, multiple gestation, and uterine fibroids limit the effectiveness of fundal height measurements for screening. Formal growth ultrasonography may be considered for these patients.