Fetal Growth Percentile Calculator

Comprehensive ultrasound-based fetal growth assessment tool. Calculate growth percentiles, detect abnormalities, and monitor fetal development throughout pregnancy.

How to Use This Calculator

Enter fetal biometric measurements from your ultrasound report. All measurements should be taken in the standard anatomical planes. The calculator uses validated Hadlock formulas and growth curves.

Gestational Age

weeks
Based on last menstrual period or first trimester ultrasound
days
For more precise dating (0-6 days)
Estimated Due Date: December 15, 2023
Third Trimester
Metric System (mm, cm)
Imperial System (inches)

Fetal Ultrasound Measurements

Enter at least one measurement for calculation. More measurements increase accuracy.

mm
Transverse diameter of fetal head at the level of thalami
mm
Circumference around outer skull table at the level of thalami
mm
Transverse section at level of stomach and umbilical vein
mm
Longest axis of femoral diaphysis, excluding distal femoral epiphysis

Understanding Fetal Growth Assessment

BPD Biparietal Diameter

Measures the transverse diameter of the fetal head at the level of the thalami. Important for dating and detecting microcephaly or macrocephaly.

  • Standard plane: Transverse view of head
  • Key landmarks: Midline falx, thalami, cavum septum pellucidum
  • Measurement: Outer to inner skull table
HC Head Circumference

Circumference around the outer skull table at the same level as BPD. More accurate than BPD for dating after 14 weeks and assessing head growth.

  • Same plane as BPD measurement
  • Ellipse drawn around outer skull
  • Less affected by head shape than BPD
AC Abdominal Circumference

Most important measurement for fetal weight estimation. Taken at the level of the stomach and umbilical vein. Sensitive indicator of fetal nutrition.

  • Key landmarks: Stomach bubble, umbilical vein, spine
  • Round or oval shape (not compressed)
  • Most variable measurement
FL Femur Length

Measures the longest axis of the femoral diaphysis. Used for dating and detecting skeletal dysplasias. Most accurate long bone measurement.

  • Bone shaft only (exclude epiphysis)
  • Horizontal beam orientation
  • Both ends clearly visible
Understanding Growth Percentiles

Percentiles indicate how a measurement compares to a reference population of the same gestational age. For example, a fetus at the 75th percentile for weight is heavier than 75% of fetuses at the same gestational age.

Percentile Range Classification Clinical Significance Follow-up
<3rd Severely Small High risk for growth restriction Close monitoring, possible intervention
3rd - 9th Small for GA (SGA) Possible growth restriction Increased surveillance
10th - 90th Appropriate for GA (AGA) Normal growth Routine care
91st - 97th Large for GA (LGA) Possible macrosomia Monitor for delivery concerns
>97th Macrosomia High risk for birth complications Delivery planning needed
Symmetric vs Asymmetric Growth Restriction
Symmetric FGR

Features:

  • All measurements proportionally small
  • HC/AC ratio normal
  • Early onset (before 32 weeks)
  • Often genetic or chromosomal
Asymmetric FGR

Features:

  • AC disproportionately small
  • HC/AC ratio increased
  • Late onset (after 32 weeks)
  • Often placental insufficiency
Fetal Growth Restriction (FGR)

Definition: Estimated fetal weight <10th percentile for gestational age

Causes:

  • Placental insufficiency (most common)
  • Maternal conditions (hypertension, diabetes)
  • Fetal abnormalities
  • Infections
  • Genetic factors

Management:

  • Increased fetal surveillance
  • Doppler studies
  • Timing of delivery
  • Maternal rest and nutrition
Macrosomia

Definition: Estimated fetal weight >90th percentile or >4000g

Risk Factors:

  • Maternal diabetes
  • Maternal obesity
  • Post-term pregnancy
  • Previous macrosomic infant

Complications:

  • Shoulder dystocia
  • Birth trauma
  • Cesarean delivery
  • Postpartum hemorrhage
Small for Gestational Age (SGA)

Definition: Estimated fetal weight <10th percentile but normal growth velocity

Key Points:

  • Not all SGA fetuses have FGR
  • Constitutionally small but healthy
  • Normal Doppler studies
  • Normal amniotic fluid

Differentiation from FGR:

  • Serial measurements show normal growth
  • Normal umbilical artery Doppler
  • Normal biophysical profile
Large for Gestational Age (LGA)

Definition: Estimated fetal weight >90th percentile

Causes:

  • Genetic predisposition
  • Maternal diabetes
  • Excessive weight gain
  • Post-term pregnancy

Management:

  • Glucose tolerance testing
  • Delivery planning
  • Neonatal hypoglycemia screening
  • Consider elective cesarean if >4500g

Ultrasound measurements have approximately ±8-10% accuracy for fetal weight estimation. Accuracy depends on:
  • Quality of ultrasound equipment
  • Experience of the sonographer
  • Fetal position and movement
  • Number of measurements taken
  • Gestational age (less accurate at extremes)

SGA (Small for Gestational Age) refers to size alone (weight <10th percentile). FGR (Fetal Growth Restriction) indicates pathological growth limitation. Key differences:
  • SGA may be constitutionally small but healthy
  • FGR has abnormal growth velocity and may have abnormal Doppler studies
  • All FGR fetuses are SGA, but not all SGA fetuses have FGR
  • FGR requires clinical intervention, while SGA may only require monitoring

The frequency depends on clinical indications:
  • Low-risk pregnancy: Typically 1-2 growth scans (20w anatomy, 32w growth)
  • High-risk pregnancy: Every 3-4 weeks from 28 weeks
  • FGR diagnosis: Every 2 weeks with Doppler studies
  • Diabetes/HTN: Every 4 weeks from 28 weeks
  • Multiple gestation: Every 4 weeks from 16 weeks

Multiple factors influence fetal growth:
  • Maternal: Nutrition, health conditions, smoking, drug use
  • Placental: Blood flow, size, function
  • Fetal: Genetics, infections, anomalies
  • Environmental: Altitude, pollution, stress
  • Medical: Medications, chronic diseases