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 Fetal Growth Restriction (FGR) aka
Intrauterine Growth Restriction (IUGR)
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Reviewed by Medical Advisory Board Percentiles
Fetal growth restriction (FGR) , also known as intrauterine growth restriction (IUGR),  is a condition in which an unborn baby (fetus) has an estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for an accurately assigned gestational age. This means that the baby weighs less than or has a belly smaller than 9 out of 10 babies of the same gestational age.  The most common causes of FGR are suboptimal perfusion of the maternal fetal circulation due to maternal or placental conditons, a naturally small fetus, and congenital syndromes in the fetus.

 Causes of Fetal Growth Restriction

Causes of  Fetal Growth Restriction

Maternal conditions that have been associated with FGR including but not limited to hypertensive disease , antiphospholipid syndrome (APLS ),diabetes with vascular diseases, renal impairment,  cigarette smoking,alcohol consumption, uncontrolled asthma, cystic fibrosis, cyanotic congenital heart disease, severe anemia, sickle cell anemia, b-thalassemia, and hemoglobin H disease

Placental Conditons

Preeclampsia, confined placental mosaicism, placental mesenchymal dysplasia, placental infarction and decidual vasculopathy, single umbilical artery, velamentous cord insertion have all been associated with FGR.

Fetal  Conditions

Up to 22% of growth restricted fetuses are  naturally small due to the size of the baby's parents, ethnic background , and the sex of the baby. About 20% of fetuses with FGR have a chromosomal or genetic syndrome, or physical malformations  such as heart defects, diaphragmatic hernia , or gastroschisis .Approximately 5 % of FGR is caused by congenital infections , with cytomegalovirus (CMV) infection being the the most common intrauterine infection in the United States.  Multiple gestations account for 3 % of all cases of FGR ; up to 30% of twins may develop FGR .


CLASSIFICATION OF FGR [2]
  • Early onset FGR: FGR diagnosed at less than 32 weeks 
    • Tends to be more severe and more likely to be associated with a congenital  syndrome than late onset FGR.
  • Late onset FGR : FGR: idiagnosed at  32 weeks or later
    • Accounts for 70% to 80% of FGR cases and is typically milder than early onset FGR . Normal Doppler studies of the umbilcal artery is not uncommon.
  • Severe FGR .The EFW  is less than  3rd percentile

Classification of FGR as symmetric or asymmetric based on the head circumference: abdominal circumference (HC/AC) ratio appears to be of limited value since the HC/AC ratio has not been found to be an independent predictor of adverse pregnancy outcomes, or of  poor growth or developmental delay in growth restricted preterm newborns.

EVALUATION [2]

  • Detailed obstetrical ultrasound for early-onset FGR
  • Prenatal diagnostic testing with chromosomal microarray (CMA) for
    • Early-onset FGR OR
    • FGR at any gestational age AND
    • Sonographic abnormalities (fetal malformations) AND/OR
    • Polyhydramnios
  • Polymerase chain reaction (PCR) for cytomegalovirus (CMV) if patent has amniocentesis
  • Evaluation may sometimes require more advanced testing methods for example methylation analysis, uniparental disomy analysis , deletion / duplication analysis , sequence analysis

    TREATMENT 

    Currently there are  no effective treatments available for FGR.  Activity restriction , and treatment with heparin or sildenafil are not recommended

     

     MONITORING

    The fetus with FGR is monitored using cardiotocography (CTG) and Doppler ultrasound of the fetal umbilical arteries after viabiity ..

    • Cardiotocography  is the electronic monitoring of the fetal heart rate and uterine contraction signals . Recurrent late fetal heart rate decelerations during CTG is an indication that the fetus should be delivered.
    • Doppler ultrasound  is used to evaluate the placenta for damage or insufficiency. Doppler ultrasound measures  the velocity of the blood flow in the umbilical arteries of the fetus. The illustrations below show blood flow through the umbilical artery during contraction of the fetal heart. (sytolic flow) . During the relaxation phase of the heartbeat there is normally continued blood flow to the placenta (end-diastolic flow). Damage or insufficiency in the placenta may be detected as decreased or absent end diastolic velocity on Doppler ultrasound.

      Normal
      S/D, PI, RI
       Less than or equal to 95%       		Decreased end diastolic velocity (EDV)
      S/D, PI, RI
      Greater than 95%       		Absent end-diastolic velocity (AEDV) Reversed end-diastolic velocity (REDV)
      S = Systolic flow ;Flow through the umbilical artery during contraction of the fetal heart.
      D       = End-diastolic flow; Continuing forward flow in the umbilical artery during the relaxation phase of the heartbeat

    MANAGEMENT [2]

    FINDINGS

    		 Frequency of
     UA Doppler     		 Frequency of Cardiotocography Frequency of ultrasound for EFW Delivery
    Normal Doppler  EFW  >= 3rd % or < 10 th% Every  week for  2 weeks.
    If stable,  then every 2 to 4 weeks    		 every week every  3 to 4  weeks 38 0/7  to 
    39 0/7  weeks
    EFW  < 3rd % every week every week every 2 weeks 37 0/7  weeks
    Decreased EDV  every week 1 to 2 times  per week every 2 weeks 37 0/7 weeks
    AEDV  Consider inpatient admission
    Corticosteroids for FLM    		 2 to 3 times per week 2 time per week if outpatient every 2 weeks 33 0/7 to
    34 0/7  weeks
    REDV Inpatient admission
    Corticosteroids for FLM    		 1 to 2 times per day every 2 weeks 30 0/7  to
    32 0/7 weeks
    EFW:= Estimated fetal weight; FLM= Fetal lung maturity

    Antenatal corticosteroids are indicated if delivery is anticipated within 7 days in a women at less than  36 6/7 weeks who has not received a previous course of antenatal corticosteroids  and has no contraindications . Magnesium sulfate is recommended for neuroprotection if delivery  before 32 weeks is anticipated.

    By Mark Curran, MD FACOG Updated 4/13/2021

    REFERENCES

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