Can a fetus with intrauterine growth restriction (IUGR) have a normal heart rate (HR)?

Can Fetal Growth Restriction Present with Normal Heart Rate?

Yes, fetuses with intrauterine growth restriction (IUGR) can absolutely have normal heart rate patterns, particularly in early stages or with compensated placental insufficiency. Normal fetal heart rate testing does not exclude IUGR and should never be used as the sole surveillance method in these high-risk pregnancies 1.

Understanding the Clinical Reality

The presence of normal cardiotocography (CTG) or nonstress testing (NST) in IUGR fetuses is common and reflects the natural progression of fetal compromise:

• Early/compensated IUGR typically maintains normal heart rate patterns, normal heart rate variability, and reactive NSTs while the fetus is still adapting to chronic hypoxemia through redistribution of blood flow 1, 2

• Heart rate changes occur late in the deterioration sequence—abnormal heart rate patterns (loss of variability, non-reactive NST) typically appear only after significant vascular changes are already present on Doppler studies 1

• Research demonstrates that IUGR fetuses can show gender-specific heart rate dynamics, with males showing lower mean heart rates and females showing lower entropy measures, but these changes may be subtle and not always clinically apparent 3

The Surveillance Hierarchy

Umbilical artery Doppler is the primary surveillance tool for IUGR, not heart rate monitoring alone 1. The evidence is clear on this hierarchy:

Primary: Doppler Assessment

• Umbilical artery Doppler should be performed weekly once IUGR is diagnosed, as it detects placental dysfunction before heart rate changes emerge 1, 2
• Doppler abnormalities progress in a predictable sequence: increased umbilical artery resistance → absent end-diastolic flow → reversed end-diastolic flow → venous Doppler changes → finally, abnormal heart rate patterns 1

Secondary: Cardiotocography

• Weekly NST or biophysical profile (BPP) testing is recommended after viability for IUGR in conjunction with Doppler assessment, not as a replacement 1, 2
• Frequency increases to twice weekly or more when absent or reversed end-diastolic flow is detected, even if heart rate remains normal 1

Critical Clinical Pitfall

The most dangerous error is assuming normal heart rate testing means the IUGR fetus is safe. This misconception can lead to delayed delivery and preventable stillbirth 1, 2. Consider this progression:

1. Weeks 1-3 of deterioration: Umbilical artery Doppler becomes abnormal, but NST remains reactive and reassuring 1
2. Weeks 3-5: Absent or reversed end-diastolic flow develops, middle cerebral artery shows brain-sparing, but heart rate may still be normal 1
3. Week 5+: Venous Doppler abnormalities appear (ductus venosus, umbilical vein pulsations), and only then does the biophysical profile become abnormal and heart rate variability decrease 1

Evidence-Based Management Algorithm

When IUGR is suspected with normal heart rate:

If umbilical artery Doppler is normal:

• Continue weekly Doppler surveillance 1, 2
• Weekly NST or BPP 1, 2
• Plan delivery at 38-39 weeks if estimated fetal weight 3rd-10th percentile 1, 2, 4

If umbilical artery shows decreased diastolic flow (but heart rate normal):

• Increase to weekly Doppler 2, 4
• Weekly cardiotocography 2
• Deliver at 37 weeks regardless of normal heart rate 1, 2, 4

If absent end-diastolic flow (even with normal heart rate):

• Doppler 2-3 times weekly 2, 4
• Increase cardiotocography frequency 2
• Deliver at 33-34 weeks regardless of reassuring heart rate patterns 1, 2, 4

If reversed end-diastolic flow (even with normal heart rate):

• Hospitalize immediately 2, 4
• Cardiotocography 1-2 times daily 2, 4
• Administer antenatal corticosteroids 1, 2
• Deliver at 30-32 weeks regardless of heart rate status 1, 2, 4

Physiologic Explanation

The fetus maintains normal heart rate through compensatory mechanisms even as placental function deteriorates 5, 6:

• Cardiac adaptation: IUGR fetuses demonstrate progressive hemodynamic changes with earlier right ventricular than left ventricular dysfunction, and diastolic changes before systolic changes 5
• Autonomic compensation: The fetus maintains heart rate variability through neuro-vegetative regulatory processes until late decompensation 6
• Brain-sparing physiology: Blood flow redistribution to vital organs (brain, heart, adrenals) preserves central nervous system function and heart rate regulation until reserves are exhausted 1

Intrapartum Considerations

Even IUGR fetuses with normal antepartum heart rate patterns require continuous electronic fetal monitoring during labor 7:

• These fetuses have limited physiologic reserve to withstand repetitive decreases in uteroplacental blood flow with contractions 7
• They may demonstrate sudden concerning changes (bradycardia, late decelerations) despite previously reassuring testing 7
• Studies report 75-95% of IUGR pregnancies with absent/reversed end-diastolic flow require cesarean delivery for intrapartum heart rate abnormalities, even when antepartum testing was reassuring 1, 4

The bottom line: Normal fetal heart rate in IUGR is common, expected in early stages, and provides false reassurance if used without Doppler assessment. Management decisions must be driven by Doppler findings and gestational age, not heart rate patterns alone 1, 2.