Intrauterine growth restriction (IUGR) refers to a fetus with an estimated weight below the 10th percentile. It can be suspected by poor maternal weight gain or a small fundal height, and is often detected on ultrasound. Causes include smoking, drugs, maternal health issues, and fetal abnormalities. Ultrasound assesses fetal anatomy, biophysical profile, and Doppler of the umbilical artery to evaluate blood flow. Abnormal Doppler readings correlate with adverse outcomes and help guide management. Serial ultrasounds may reduce emergency C-sections compared to cardiotocography alone for monitoring restricted growth fetuses.

1. DIAGNOSTIC IMAGING PATHWAYS
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INTRAUTERINE GROWTH RESTRICTION (IUGR)
• Intrauterine growth restriction (IUGR) refers to a fetus with an estimated fetal weight below the 10th
percentile corrected for sex and ethnicity which has features of chronic hypoxia and/or malnutrition.
However, a consensus does not exist for the definition of IUGR. 1
• It is associated with adverse fetal outcomes including acidosis, stillbirth, oligohydramnios, low-birth
weight, and adverse events during labour including fetal distress in labour. 1,2
• IUGR is often suspected by poor maternal weight gain, and a fundal height that is less than expected
for the gestational age and is an indication for ultrasound at presentation. Additionally, it may be
detected during the routine 18-20 week scan that is recommended as best practice within Australia.
• Two different growth patterns for IUGR have been described. In symmetric IUGR, all biometric
measurements are affected to a similar degree, whilst the head growth is spared relative to body
growth with asymmetric IUGR. 1
• Causes and risk factors for intrauterine growth restriction include: 1
• Smoking during pregnancy
• Illicit drug use in pregnancy
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2. • Low maternal body mass index
• Deficient antenatal care
• Fetal abnormalities: chromosomal abnormalities, malformations
• Maternal infections: toxoplasmosis, rubella, CMV, herpes
• Chronic maternal disease: diabetes mellitus, hypertension, renal disease
ULTRASOUND
• Conventional and Doppler ultrasonography are used to assess fetal wellbeing through the
following parameters: 3,4,5,6
• Fetal anatomy: measurements include biparietal diameter, head circumference,
abdominal circumference, femur length, and estimation of fetal weight. Abdominal
circumference is the most sensitive measurement for assessing fetal wellbeing.
• Biophysical profile: includes fetal heart rate, breathing, movements, tone, amniotic
fluid and duplex Doppler waveform of the umbilical artery, including a calculation of
the systolic to diastolic (S/D) ratio.
• Percentile charts are used to assess the estimated fetal weight for age. Normal values are
arbitrarily chosen as between the 10th and 90th percentiles.
• During early pregnancy, the placental vascular resistance is normally high, and in normal
pregnancies vascular resistance falls so that by 20 weeks of gestation, there is continuous
diastolic flow toward the maternal system through the umbilical arteries. 4,5
• Changes in the Doppler characteristics of the umbilical artery may reflect IUGR and placental
dysfunction. Changes in the end-diastolic velocity of the umbilical artery range from reduced,
to absent or reversed and may indicate progressive abnormal increases in the placental
circulatory resistance. The normal S/D ratio is less than 3.5, and varies with gestational age. 4,5
• Doppler studies of the umbilical artery alone are not diagnostic of intrauterine growth
restriction as the sensitivity is low. A combination of conventional and Doppler ultrasound has a
sensitivity, specificity, positive predictive value and negative predictive value of 31%, 99%, 77%,
and 93% respectively. 7
• Increasingly, middle cerebral artery, ductus venosus, and umbilical vein doppler studies are
being used to aid assessment. 8
• In diagnosed IUGR, the degree of umbilical artery abnormality directly correlates with adverse
fetal outcomes and adverse events during labour and the immediate post-partum period. It can
be used to guide management and has been shown to significantly reduce the risk of perinatal
mortality by 38%, but without a significant effect on neonatal morbidity. 4,5,7,9
• If IUGR is diagnosed and there are no indications for immediate delivery, fetal monitoring is
appropriate. This usually consists of serial cardiotocography and ultrasound (biophysical profile,
S/D ratios, and assessment of fetal growth). One randomised control trial has shown that
compared to serial cardiotocography, serial Doppler ultrasound of the umbilical arteries
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3. significantly reduces the need for emergency cesarean deliveries for fetal distress in-utero.
1,3,10
REFERENCES
1. Nyberg DA, Abuhamad A, Ville Y. Ultrasound Assessment of Abnormal Fetal Growth. Seminars
in Perinatology 2004;28:3-22. (Review article)
2. Smith-Bindman R, Chu PW, Ecker JL, Feldstein VA, Filly RA, Bacchetti P. US Evaluation of Fetal
Growth: Predictors of Neonatal Outcomes. Radiology 2002;223:153-61. (Level III evidence)
3. Cragio SD. The Role of Ultrasound in the Diagnosis and Management of Intrauterine Growth
Retardation. Seminars in Perinatology 1994;18:292-304. (Review article)
4. Harman CR, Baschat AA. Comprehensive assessment of fetal wellbeing: which Doppler tests
should be performed. Curr Opin Obstet Gynecol 2003;15:147-57. (Review article)
5. Dudiak CM, Salomon CG, Posniak HV, Olson MC, Flisak ME. Sonography of the Umbilical Cord.
Radiographics 1995;15:1035-50. (Review article)
6. Australasian Society for Ultrasound in Medicine (ASUM). Guidelines for the Performance of
Third Trimester Ultrasound. ASUM Guidelines revised 1999. (Position Statement)
7. Ott WJ. Diagnosis of Intrauterine Growth Restriction: Comparison of Ultrasound Parameters.
Am J Perinatology 2002;19:133-7. (Level III evidence)
8. Harman CR, Baschat AA. Arterial and Venous Dopplers in IUGR. Clin Obstet Gynaecol
2003;46:931-46. (Review article)
9. Alfirevic Z, Neilson JP. Doppler ultrasonography in high-risk pregnancies: Systematic review
with meta-analysis. Am J Obstetrics and Gynaecology 1995;172: 1379-87. (Level II evidence).
Click here to view reference
10. Williams KP, Farquharson DF, Bebbington M, et al. Screening for fetal well-being in a high-risk
pregnant population comparing the nonstress test with umbilical artery Doppler
velocimetry: a randomised controlled clinical trial. Am J Obstet Gynecol 2003;188:1366-71.
(Level II evidence). Click here to view reference
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