Asymmetric Intrauterine Growth Restriction Causes and Characteristics

Etiology and Pathophysiology

The American College of Obstetricians and Gynecologists notes that placental insufficiency is the most common cause of asymmetric IUGR, accounting for 25-30% of all fetal growth restriction cases 1
Placental insufficiency due to suboptimal perfusion of the maternal-placental circulation is the leading cause, responsible for 25-30% of all FGR cases 1
The American Journal of Obstetrics and Gynecology reports that chromosomal disorders and congenital malformations account for approximately 20% of FGR cases 1

The American College of Radiology suggests that earlier in gestation, chromosomal anomalies, syndromes, and viral infections are more common etiologies 2, 3
Later in gestation, placental insufficiency predominates, especially related to hypertension and maternal vascular disease 2, 3
Asymmetric FGR with "head-sparing" is characteristically more common in late-onset cases, where placental insufficiency leads to preferential blood flow redistribution to protect the fetal brain at the expense of abdominal/somatic growth 2, 3

The American College of Obstetricians and Gynecologists recommends that maternal history of hypertensive disorders is a key association with late-onset asymmetric FGR 4, 5
A detailed fetal structural survey should have been performed prenatally, as approximately 10% of fetuses with FGR have congenital anomalies 2

Chromosomal disorders and congenital malformations together account for ≈ 20 % of all IUGR cases, making them the second‑most common cause after placental insufficiency. 6

Chromosomal microarray analysis (CMA) is recommended for unexplained isolated IUGR diagnosed before 32 weeks (GRADE 1C). This test provides a 4–10 % incremental diagnostic yield over standard karyotyping. 6
When amniocentesis is performed for unexplained IUGR, polymerase chain reaction (PCR) testing for cytomegalovirus (CMV) should be offered. 6

Do not screen for toxoplasmosis, rubella, or herpes in the absence of specific risk factors, as routine testing adds no clinical benefit. 6

After an IUGR diagnosis, serial umbilical artery Doppler assessments should be performed to monitor for fetal deterioration. 6

Ordering unnecessary infectious disease screening (toxoplasmosis, rubella, herpes) without risk factors wastes resources and may delay appropriate management. 6