Fetal Growth Restriction: updated review of diagnosis and management

1. Definition and classification

• Estimated fetal weight (EFW) below the 10th centile, or
• Abdominal circumference (AC) below the 10th centile for gestational age, using a validated population-based reference such as Hadlock.

Clinically useful categories

2. Etiology and risk assessment

Maternal and placental factors

• Previous FGR, stillbirth, placental abruption, or preeclampsia
• Chronic hypertension, preeclampsia, renal disease
• Diabetes with vascular disease
• Antiphospholipid syndrome and some autoimmune disorders
• Smoking, alcohol, cocaine or other substances
• Significant malnutrition or poor gestational weight gain
• Certain drugs, including some beta-blockers
• Placental lesions, abnormal cord insertion, placental insufficiency

Fetal factors

• Aneuploidy and genetic syndromes
• Structural anomalies
• Congenital infection, especially CMV when otherwise unexplained early FGR is accompanied by suggestive findings
• Multiple pregnancy, particularly monochorionic gestations

3. Diagnosis

A. Establish accurate gestational age

B. Clinical screening

• Measure symphysis-fundal height after 24 weeks.
• A lag of approximately 3 cm or more should prompt ultrasound, although clinical measurement is an imperfect screening test.
• High-risk patients require serial sonographic assessment rather than relying only on fundal height.

C. Ultrasound assessment

1. Biometry
   • BPD, HC, AC, FL
   • EFW percentile and AC percentile
   • Plot values on a consistent growth standard.
2. Growth velocity
   • A single low EFW identifies a small fetus.
   • Serial measurements distinguish a stable constitutionally small fetus from progressive growth restriction.
   • In most cases, repeat growth scans should be at least 2 weeks apart, commonly every 3-4 weeks, because shorter intervals are vulnerable to measurement error.
3. Amniotic fluid
   • Oligohydramnios supports placental dysfunction and affects surveillance and delivery planning.
4. Detailed structural survey
   • Particularly important in FGR diagnosed before 32 weeks, severe FGR, disproportionate growth, or when other ultrasound abnormalities are present.
5. Placenta and cord
   • Evaluate placental appearance, cord insertion, and fetal anatomy.

D. Umbilical artery Doppler: the central surveillance test

• Normal UA Doppler in a small fetus with preserved interval growth is reassuring and favors constitutional smallness, though it does not eliminate risk.
• Decreased diastolic flow or UA PI/S:D ratio above the 95th centile suggests placental insufficiency.
• AEDV indicates major placental disease and substantial fetal risk.
• REDV is a preterminal warning sign requiring urgent tertiary-level management.

E. Other Dopplers

• Middle cerebral artery (MCA) Doppler / cerebroplacental ratio (CPR): can show cerebral vasodilatation, or “brain-sparing,” especially in late FGR. It may add prognostic information, but SMFM does not recommend MCA, CPR, ductus venosus, or uterine artery Doppler as a routine determinant of management in all FGR cases.
• Ductus venosus Doppler: mainly useful in specialized early-onset FGR pathways; abnormality may signal impending cardiovascular decompensation.
• Uterine artery Doppler: useful for risk stratification in some settings, but not a stand-alone diagnostic test for FGR.

F. Fetal surveillance

4. Evaluation after diagnosis

Early-onset or unexplained FGR

• Perform a detailed anatomic ultrasound.
• Offer diagnostic genetic testing, generally amniocentesis with chromosomal microarray when FGR is unexplained, early, or associated with malformations/polyhydramnios.
• Test for CMV by amniotic-fluid PCR if amniocentesis is undertaken in unexplained FGR. Routine broad TORCH screening is not recommended without exposure history or suggestive fetal findings.
• Assess maternal blood pressure, urine protein where appropriate, platelet count, renal and liver function when preeclampsia is suspected.

Distinguishing pathological FGR from constitutional SGA

• EFW below the 3rd centile
• Reduced growth velocity
• Abnormal UA Doppler
• Oligohydramnios
• Maternal hypertensive disease or other placental-risk condition
• Abnormal MCA/CPR, where used
• Early presentation
• Associated fetal anomaly or abnormal genetic testing

5. Management principles

A. Treat maternal disease and modify reversible risks

• Optimize control of chronic hypertension, diabetes, renal disease, and autoimmune disease.
• Stop smoking, alcohol, and illicit substances.
• Address nutritional deficiency where present.
• Monitor closely for preeclampsia.

B. What should not be used solely to treat FGR

• Low-molecular-weight heparin solely to prevent recurrent FGR
• Sildenafil as in-utero FGR treatment
• Activity restriction or bed rest

C. Antenatal corticosteroids and magnesium sulfate

• Give antenatal corticosteroids when preterm delivery is anticipated within 7 days:
  • before 33 weeks 6 days, and
  • in selected patients at 34 weeks 0 days to 36 weeks 6 days who meet local criteria and have not received a prior course.
• Give magnesium sulfate for fetal neuroprotection when delivery before 32 weeks is likely.

D. Site of care

• Early, severe, or progressive FGR
• AEDV or REDV
• Major anomaly or suspected genetic disorder
• Preeclampsia with severe features
• Anticipated very preterm delivery

6. Timing of delivery

SMFM delivery recommendations for singleton FGR

7. Mode of delivery and intrapartum care

• Vaginal birth or induction is reasonable for many term FGR pregnancies with normal or mildly abnormal surveillance.
• Continuous electronic fetal monitoring is generally appropriate in labor because FGR fetuses have reduced reserve.
• Cesarean delivery should be considered with AEDV/REDV or when fetal status is non-reassuring, recognizing that prematurity, presentation, and maternal status also matter.
• Alert neonatology before delivery, particularly for preterm or severe FGR.

8. Prevention in a future pregnancy

• Review placental histopathology, neonatal outcome, and the likely mechanism of FGR.
• Identify and manage chronic hypertension, diabetes, renal disease, autoimmune disease, and smoking.
• For patients at high risk of preeclampsia, use low-dose aspirin according to applicable preeclampsia-prevention criteria. Aspirin is not prescribed solely because of a history of isolated FGR unless the patient also meets those risk criteria.
• Use early dating, an anatomic scan, serial growth assessment, and antenatal surveillance tailored to recurrence risk.

Practical management algorithm

1. Suspect small fetus from fundal-height lag or routine scan.
2. Confirm dating and perform ultrasound: EFW/AC percentile, anatomy, fluid, placenta, UA Doppler.
3. Classify risk:
   • EFW 3rd-10th centile with normal UA Doppler and normal growth velocity: likely low-risk SGA/FGR.
   • EFW below 3rd centile, falling growth velocity, oligohydramnios, or abnormal UA Doppler: pathological FGR.
4. Investigate early/unexplained cases: detailed anatomy, offer microarray, targeted CMV testing when indicated, evaluate maternal disease.
5. Start surveillance: serial growth, UA Doppler, and CTG/NST after viability.
6. Escalate with AEDV/REDV or non-reassuring tests: tertiary care, corticosteroids, magnesium sulfate when eligible, and delivery at the recommended gestation or sooner if maternal/fetal compromise occurs.
7. Plan delivery by Doppler severity and gestational age, with neonatal team involvement.

Key takeaways

• FGR is a syndrome of impaired growth potential, not merely a fetus below the 10th centile.
• Umbilical artery Doppler is the key test that directs surveillance intensity and timing of birth.
• Early-onset FGR warrants detailed anatomic and genetic evaluation.
• There is no proven in-utero therapy that restores placental function. Management is surveillance, maternal optimization, antenatal maturation therapy when preterm birth is expected, and timely delivery.
• Deliver at 38-39 weeks for uncomplicated FGR with normal UA Doppler, earlier for severe FGR or abnormal Doppler patterns.

• Number, size, and location of fibroids removed
• Depth of the uterine incision and whether the cavity was opened
• Quality and number of layers of myometrial suturing
• Any postoperative complications
• Fertility factors, especially maternal age