Fetal Growth Restriction Diagnosis and Management

Defining Normal vs. Abnormal Growth

• The Society for Maternal-Fetal Medicine establishes that a fetus is considered to have normal growth when the estimated fetal weight (EFW) or abdominal circumference (AC) is at or above the 10th percentile for gestational age, with fetal growth restriction (FGR) defined as EFW or AC <10th percentile 1, 2, 3
• Severe FGR is associated with EFW <3rd percentile, and is linked to stillbirth rates up to 2.5% 1, 2

Clinical Significance of the 10th Percentile Threshold

• Fetuses below the 10th percentile have approximately 1.5% stillbirth rate, which is twice the rate of normally growing fetuses, and are more likely to experience severe acidosis at birth, low 5-minute Apgar scores, and NICU admissions 1, 2
• Below the 5th percentile, stillbirth rates increase to 2.5% 1, 2

Management Based on Growth Percentiles

• For fetuses below the 10th percentile, serial umbilical artery Doppler assessment should be performed to monitor for deterioration, with management intensity escalating based on severity 3
• The American College of Obstetricians and Gynecologists recommends that fetuses in the 3rd-10th percentile with normal Doppler should have weekly umbilical artery Doppler and delivery at 38-39 weeks 3
• For fetuses with absent end-diastolic velocity, Doppler should be performed 2-3 times per week, with delivery at 33-34 weeks 3
• For fetuses with reversed end-diastolic velocity, delivery is recommended at 30-32 weeks 3

Important Caveats

• The Society for Maternal-Fetal Medicine recommends abandoning the term "intrauterine growth restriction (IUGR)" in favor of "fetal growth restriction (FGR)" for prenatal diagnosis, and reserving the term "small for gestational age (SGA)" for newborns with birthweight <10th percentile 1, 2
• Accurate pregnancy dating is an essential prerequisite for diagnosing FGR, with dating best established using first-trimester crown-rump length to either confirm menstrual dates or assign new dates 1

Fetal Growth Restriction Diagnosis and Management

Diagnostic Criteria

• The American College of Obstetricians and Gynecologists recommends that fetuses with estimated fetal weight <3rd percentile be considered as having severe Fetal Growth Restriction (FGR), with stillbirth rates up to 2.5%, regardless of other findings 4
• Abnormal umbilical artery Doppler, such as elevated resistance, absent or reversed end-diastolic flow, confirms placental insufficiency and indicates pathological growth restriction 4, 5
• Abnormal middle cerebral artery or cerebroplacental ratio indicates fetal brain-sparing redistribution and is a marker of FGR 4, 6
• Oligohydramnios suggests chronic placental dysfunction and is a severity marker for FGR 4

Growth Velocity and Risk Stratification

• Crossing centiles downward or inadequate interval growth (AC change <5mm over 14 days, or >30% reduction in growth velocity) indicates progressive pathology and is a criterion for FGR diagnosis 4
• Four of six international guidelines (67%) incorporate reduced growth velocity into FGR definitions, highlighting its importance in diagnosing growth restriction 4

Postnatal Considerations

• The American College of Obstetricians and Gynecologists provides specific guidance on the management of SGA newborns, noting that they may be constitutionally small and healthy, requiring only standard newborn care 7
• IUGR infants face acute complications, including perinatal asphyxia, hypothermia, hypoglycemia, and polycythemia, plus long-term risks of neurodevelopmental handicaps and adult metabolic disease, and require interdisciplinary follow-up 7, 4

Fetal Growth Restriction – Risks, Outcomes, and Clinical Guidance

Short‑Term Perinatal Risks

• Fetuses whose estimated weight is below the 10th percentile have a stillbirth rate of approximately 1.5 %—about twice that of normally growing fetuses【@1】.
• When fetal weight falls below the 5th percentile, the stillbirth rate rises to roughly 2.5 %【@1】.
• Preterm FGR increases the risk of perinatal death by 2‑ to 5‑fold compared with term FGR fetuses【@1】.
• The poorest outcomes occur in fetuses with estimated weights below the 3rd percentile or with abnormal fetal Doppler studies (e.g., absent or reversed end‑diastolic flow)【@1】.
• Newborns with birthweight < 10th percentile are markedly more likely to develop severe acidosis at birth, receive low 5‑minute Apgar scores, and require admission to a neonatal intensive‑care unit【@1】.
• Severity of growth restriction drives risk: fetuses below the 3rd percentile have the highest adverse‑outcome profile【@1】.
• Abnormal umbilical‑artery Doppler findings (absent or reversed end‑diastolic velocity) significantly worsen prognosis【@1】【@2】.
• Prematurity compounds all adverse outcomes associated with FGR【@1】.

Long‑Term Health Consequences

• FGR is linked to metabolic programming that raises the lifetime risk of metabolic syndrome and related cardiovascular and endocrine diseases【@1】.
• Children and adults who experienced FGR have an increased incidence of neurodevelopmental delay and related handicaps, warranting ongoing monitoring【@3】【@4】.

Etiology and Pathophysiology

• Placental insufficiency—suboptimal maternal‑placental perfusion—is the most common cause of FGR, accounting for roughly 25‑30 % of cases【@1】.
• Chromosomal disorders and congenital malformations contribute to about 20 % of FGR cases【@1】.
• Early‑onset FGR (diagnosed before 32 weeks) is especially associated with fetal or chromosomal abnormalities, present in up to 20 % of such cases【@2】.

Clinical Assessment Pitfalls

• A major error is failing to differentiate constitutionally small but healthy fetuses from true FGR due to placental insufficiency; the latter requires intensified surveillance and possible intervention【@3】【@4】.

Diagnostic Criteria and Management of Fetal Growth Restriction

Diagnostic Thresholds

• The Society for Maternal‑Fetal Medicine defines fetal growth restriction (FGR) as present when either the estimated fetal weight (EFW) or the abdominal circumference (AC) is below the 10th percentile for gestational age【8】【9】.
• According to the Society for Maternal‑Fetal Medicine, an EFW < 10th percentile is the traditional standalone criterion for diagnosing FGR【8】【9】.
• The Society for Maternal‑Fetal Medicine also states that an AC < 10th percentile is an equally valid standalone diagnostic criterion, even when the EFW is within normal limits【8】【9】.

Severity Stratification

• Severe FGR is defined by an EFW < 3rd percentile, irrespective of umbilical artery Doppler findings【8】.
• In pregnancies with severe FGR, the stillbirth rate can be as high as 2.5 %【8】.
• Moderate FGR is characterized by an EFW between the 3rd and 10th percentiles with a normal umbilical artery Doppler【8】.
• The stillbirth rate for moderate FGR is approximately 1.5 %, roughly double that of normally growing fetuses【8】.

Prerequisites for Diagnosis

• Accurate pregnancy dating is mandatory before diagnosing FGR; gestational age must be established reliably to calculate percentiles【9】.

Terminology Recommendations

• The Society for Maternal‑Fetal Medicine recommends abandoning the term “intrauterine growth restriction (IUGR)” in favor of “fetal growth restriction (FGR)” for prenatal diagnosis【8】【9】.
• The term “small for gestational age (SGA)” should be reserved exclusively for newborns whose birthweight is <10th percentile, distinguishing post‑natal findings from prenatal diagnosis【8】【9】.
• These definitions are not interchangeable: FGR refers to a prenatal ultrasound‑based diagnosis of impaired growth, whereas SGA describes a post‑natal measurement of birthweight relative to gestational age【8】【9】.

Estimated Fetal Weight Percentiles and Clinical Implications at 35 Weeks Gestation

Definition and Percentile Thresholds

• The Society for Maternal‑Fetal Medicine defines a normal estimated fetal weight (EFW) at 35 weeks as being at or above the 10th percentile for gestational age【10, 11】.
• At 35 weeks, the 3rd percentile corresponds to an EFW of roughly 1,800–1,900 g, indicating severe growth restriction【10, 12】.

Clinical Outcomes by Percentile

• Fetuses with an EFW ≥ 10th percentile have perinatal risk profiles comparable to the general obstetric population【10, 11】.
• When the EFW falls between the 3rd and 10th percentiles, the stillbirth rate rises to about 1.5 %—approximately twice the rate seen in normally growing fetuses【10, 11】.
• An EFW < 3rd percentile is associated with a stillbirth rate of roughly 2.5 %, reflecting severe fetal growth restriction irrespective of Doppler findings【10, 12, 13】.

Ultrasound Assessment Accuracy

• Using multiple biometric parameters (biparietal diameter, head circumference, abdominal circumference, femur length) improves the accuracy of ultrasound‑derived EFW compared with single‑parameter formulas【13】.

Guidelines for Accurate Assessment

• Accurate pregnancy dating—preferably by first‑trimester crown‑rump length measurement—is required before interpreting EFW percentiles【13】.
• Population‑based growth references (e.g., Hadlock curves) are recommended over customized charts for consistent diagnostic criteria【14】.

Recommended Terminology

• “Fetal growth restriction (FGR)” denotes a prenatal ultrasound diagnosis of EFW < 10th percentile【10, 12】.
• “Small for gestational age (SGA)” should be reserved for newborns whose birth weight is <10th percentile【10, 12】.
• The term “intrauterine growth restriction (IUGR)” is discouraged and should be replaced by “FGR” in prenatal contexts【10, 11, 12】.

Management Recommendations at 35 Weeks

• Umbilical artery Doppler assessment is indicated when the EFW is below the 10th percentile to differentiate pathological restriction from constitutional smallness【10, 12】.