Fetal Growth Restriction (FGR): Causes, Diagnosis, and Treatment

Fetal growth restriction (FGR), also known as intrauterine growth restriction (IUGR), occurs when a baby in the womb is smaller than expected for its gestational age, typically defined as an estimated fetal weight below the 10th percentile. This condition affects about 5-10% of pregnancies and raises risks of complications like low birth weight and neonatal issues, but early detection and management can improve outcomes.

Defining and Classifying FGR

FGR is diagnosed via ultrasound measuring fetal biometrics such as head circumference, abdominal circumference, and femur length, with abdominal circumference often being the most sensitive indicator. It is classified into symmetrical and asymmetrical types. Symmetrical FGR, comprising 20-30% of cases, involves proportional smallness across all measurements, often due to early intrinsic fetal issues like genetic anomalies. Asymmetrical FGR, more common, shows a normal head size with a reduced abdominal circumference, typically from late-onset placental insufficiency sparing brain growth via the brain-sparing effect.

Primary Underlying Causes

The roots of FGR stem from disruptions in the fetal-placental-maternal interface, leading to inadequate nutrient and oxygen delivery. Causes are grouped into maternal, placental/fetal membrane, and fetal factors.

Maternal Contributors

Conditions impairing blood flow or nutrition include hypertensive disorders like preeclampsia, which affects 8% of pregnancies in Western countries and causes vascular changes reducing placental perfusion. Other risks: chronic hypertension, diabetes with vascular complications, renal disease, severe anemia (e.g., sickle cell), autoimmune disorders like antiphospholipid syndrome, and cyanotic heart disease. Lifestyle factors such as smoking, alcohol, cocaine, or illicit drug use significantly heighten risk by constricting vessels and reducing oxygenation. Poor nutrition, low pre-pregnancy weight, inadequate gestational gain, high altitude, and multiple prior small babies also contribute; recurrence risk is around 20%.

Placental and Cord Abnormalities

Placental insufficiency from poor spiral artery remodeling is the leading cause, seen in uteroplacental issues like infarction, abruption, previa, or mosaicism. Cord problems including single umbilical artery, velamentous insertion, or hypercoiling obstruct flow, mimicking starvation. These reduce perfusion, prompting fetal adaptations like redirecting blood to vital organs.

Fetal-Specific Factors

Intrinsic issues account for 20-30% of cases: chromosomal anomalies (e.g., trisomy 13/18 in 50% of affected fetuses), genetic syndromes (e.g., Silver-Russell), congenital malformations (heart defects, gastroschisis), or infections (5-10% globally; CMV most common in the US, plus toxoplasmosis, syphilis). Multiples like twins have up to 30% FGR risk due to shared resources.

Spotting the Signs in Pregnancy

Many cases are asymptomatic, detected routinely via fundal height measurements lagging 3-4 cm behind gestational age or ultrasound. Maternal clues include high blood pressure, protein in urine, reduced fetal movements, or bleeding. Advanced signs in severe cases: oligohydramnios (low amniotic fluid).

How FGR is Diagnosed

Diagnosis relies on serial ultrasounds confirming EFW or AC <10th percentile, plotted on growth charts. Doppler ultrasound assesses umbilical artery flow; absent/reversed end-diastolic flow signals severe compromise. Amniotic fluid index, fetal echocardiography, and non-stress tests monitor well-being. Genetic testing (amniocentesis) rules out anomalies in early symmetrical cases.

Management Approaches During Pregnancy

Goals: optimize growth, prevent stillbirth. No medication universally reverses FGR; focus is surveillance and timely delivery. Low-dose aspirin (from 12 weeks) may prevent preeclampsia-related FGR in high-risk women. Bed rest is discouraged as it risks clots without benefit. Frequent monitoring (twice-weekly Dopplers, biophysical profiles) guides timing.

• Mild FGR (near 10th percentile): Weekly ultrasounds, continue to 39 weeks if stable.
• Moderate (3rd-10th percentile): Biweekly Dopplers; deliver by 38-39 weeks.
• Severe (<3rd percentile or abnormal Dopplers): Hospitalization, steroids for lung maturity, deliver at 32-34 weeks or earlier if deteriorating.

C-section is common if fetal distress or malposition; vaginal birth possible in stable cases.

Delivery and Immediate Post-Birth Care

Timing balances prematurity risks vs. intrauterine demise (4-8x higher in FGR). Neonates often need NICU for hypoglycemia, hypothermia, polycythemia, or respiratory distress. Blood sugar checks, warming, and feeding support are standard.

Potential Long-Term Effects

FGR babies face 5-10x higher perinatal mortality, plus neonatal morbidities like NEC or IVH. Survivors risk cognitive delays, metabolic syndrome, hypertension in adulthood (Barker hypothesis). Catch-up growth occurs in 80-90%, but monitoring is key.

Prevention Strategies for Future Pregnancies

Optimize health pre-conception: quit smoking/drugs, manage hypertension/diabetes, gain healthy weight. Low-dose aspirin for high-risk, folic acid, balanced diet. In recurrences, screen early.

Frequently Asked Questions

Can FGR be prevented entirely?

Not always, but risks drop with smoking cessation, blood pressure control, and prenatal care.

Does FGR mean my baby will have lifelong problems?

Many thrive with early intervention; long-term risks exist but vary by severity.

How often are ultrasounds needed for FGR?

Depends on severity: weekly to every 2-3 days in high-risk cases.

Is bed rest recommended for FGR?

No, evidence shows no growth benefit and added thrombosis risk.

What if FGR is found late in pregnancy?

Close monitoring; delivery may be induced if lungs are mature.