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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.  FGR may be due to  fetal , placental conditions., or maternal conditions

Causes of  Fetal Growth Restriction

Fetal  Conditions

Up to 22% of 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 have FGR  caused by chromosomal or genetic syndromes, 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 .


Placental Conditons ( 20 -35%)

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

Maternal Conditons

Maternal consitions 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


CLASSIFICATION OF FGR
  • Early onset FGR: FGR diagnosed at less than 32 weeks 
    • Tends to be more severe and more likely to be assoiated 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

Detailed obstetrical ultrasound to look for malformations
Chromosomal microarray analysis (CMA)* for:
Early-onset FGR
Abnormalies found on ultrasound examinationPolyhydramnios


PCR CMV on amnioc fluid if  amniocentesis is done

may 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

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 4/12/2021

REFERENCES

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