Normal Fetal Growth Percentile
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. 1
Defining Normal vs. Abnormal Growth
The Society for Maternal-Fetal Medicine establishes clear thresholds for fetal growth assessment:
- Normal growth: EFW or AC ≥10th percentile 1
- Fetal growth restriction (FGR): EFW or AC <10th percentile 1
- Severe FGR: EFW <3rd percentile, associated with stillbirth rates up to 2.5% 1
Population-based fetal growth references (such as Hadlock curves) should be used to determine fetal weight percentiles rather than customized growth charts. 1 This recommendation is based on prospective studies that failed to demonstrate superiority of individualized growth assessment in improving clinical outcomes. 1
Clinical Significance of the 10th Percentile Threshold
The 10th percentile cutoff is clinically meaningful because it identifies fetuses at increased risk for adverse outcomes:
- Fetuses below the 10th percentile have approximately 1.5% stillbirth rate—twice the rate of normally growing fetuses 1
- These infants are more likely to experience severe acidosis at birth, low 5-minute Apgar scores, and NICU admissions 1
- Below the 5th percentile, stillbirth rates increase to 2.5% 1
Management Based on Growth Percentiles
For fetuses in the 18th percentile or higher (above the 10th percentile), routine prenatal care without intensified surveillance is appropriate. 2 This includes:
- No additional growth ultrasounds beyond standard prenatal protocol 2
- No Doppler evaluation of umbilical artery 2
- No weekly non-stress testing 2
- Delivery at 39-40 weeks following standard low-risk pregnancy recommendations 2
For fetuses below the 10th percentile, serial umbilical artery Doppler assessment should be performed to monitor for deterioration. 1 Management intensity escalates based on severity:
- 3rd-10th percentile with normal Doppler: Weekly umbilical artery Doppler, delivery at 38-39 weeks 1, 3
- <3rd percentile with normal Doppler: Weekly Doppler, delivery at 37 weeks 1, 3
- Absent end-diastolic velocity: Doppler 2-3 times per week, delivery at 33-34 weeks 1, 3
- Reversed end-diastolic velocity: Delivery at 30-32 weeks 1, 3
Important Caveats
The term "intrauterine growth restriction (IUGR)" should be abandoned in favor of "fetal growth restriction (FGR)" for prenatal diagnosis. 1 The term "small for gestational age (SGA)" should be reserved for newborns with birthweight <10th percentile. 1
Accurate pregnancy dating is an essential prerequisite for diagnosing FGR. 1 Dating is best established using first-trimester crown-rump length to either confirm menstrual dates or assign new dates. 1
If a fetus initially in a normal percentile (e.g., 18th percentile) subsequently crosses two percentile lines or falls below the 10th percentile, reevaluation with detailed ultrasound and initiation of Doppler surveillance is warranted. 2 This change in growth trajectory may indicate developing placental insufficiency requiring closer monitoring. 2