Fetal Growth Restriction

KEY FACTS

Terminology

•
Fetus is pathologically small (growth restricted)
- ○
  Fetal growth restriction (FGR)
- ○
  Intrauterine growth restriction
•
Small for gestational age
- ○
  Fetus is small but healthy, not growth restricted

Imaging

•
Most common cause of FGR is placental insufficiency
- ○
  Estimated fetal weight (EFW) < 5th-10th percentile
- ○
  Abdominal circumference (AC) < 5-10 percentile
- ○
  Abnormal umbilical artery (UA) Doppler values
  - –
    Initial ↑ systolic:diastolic (S:D) ratio
  - –
    Eventual absent end diastolic flow
  - –
    Final reversed end diastolic flow
- ○
  Oligohydramnios
•
Other findings with FGR
- ○
  Uterine artery postsystolic notch (early finding)
- ○
  Ductus venosus shows reversed A-wave (late finding)
- ○
  “Brain sparing” physiology (late finding)
  - –
    Middle cerebral artery S:D ratio < UA S:D ratio
•
FGR associations
- ○
  Twin-twin transfusion
- ○
  Triploidy, trisomy 18, trisomy 13
- ○
  Anomalies (such as gastroschisis)

Clinical Issues

•
Is pregnancy dated correctly
- ○
  Cannot assess growth if dating is incorrect
•
FGR fetuses have 4x higher rates of adverse outcome

Scanning Tips

•
Good AC measurement necessary for accurate EFW
•
Well-performed biophysical profile testing is key
- ○
  Determines risk for fetal acidosis and drives delivery plan
•
Perform UA Doppler at midcord level when fetus is at rest

In this 28-week pregnancy with FGR and oligohydramnios, the UA demonstrates absent diastolic flow

and occasional reversal of diastolic flow

. High resistive flow in the UA is a hallmark finding with FGR from placental insufficiency. Reversal of flow is associated with a higher incidence of in utero fetal demise.