ISUOG Recommendations for Preeclampsia Prevention: Combined Screening and the Role of Ultrasound

SUMMARY:

The ISUOG Clinical Standards Committee, based on the latest evidence, has released practice guidelines that provide recommendations regarding the role of ultrasound in screening for and follow-up of preeclampsia. Preventative strategies (such as low-dose aspirin) for preeclampsia are effective if started in the first trimester and should begin as soon as high-risk status is identified.  

Given the superiority of combined screening, the use of Doppler cut-offs as a standalone screening modality should be avoided if combined screening is available (GRADE OF RECOMMENDATION: B)

Note: Screening refers to identification of at risk cases that may lead to prevention | Prediction refers to ability to identify at risk cases, but no evidence available regarding improved outcomes  

Combined Screening
Ultrasound Only
Multifetal Pregnancies

KEY POINTS:

Combined Screening (10-13 weeks) – Preferred where available   

• ASPRE trial results with a 10% FPR (see ASPRE summary in ‘Related ObG Topics’ below) 
  • 100% detection rate for preeclampsia <32 weeks 
  • 75% detection rate for preeclampsia <37 weeks 
  • 43% detection rate for preeclampsia ≥37 weeks 

Combined screening approach is preferred over ultrasound alone and includes the following (see summary of ASPRE algorithm details in ‘Related ObG Topics’ below)   

• Maternal factors 
  • History | Demographics | CVD and metabolic profile  
• Maternal arterial BP
• Placental growth factor (PlGF) 
• Pulsatility index (PI) should be used to assess uterine artery resistance  
  • Transabdominal approach preferred as used for most studies   
  • Transabdominal: Use color flow mapping on a mid-sagittal view of the uterus at the level of the cervical internal os (transabdominal approach)  
  • Transvaginal: Also obtain mid-sagittal view of the uterus, with lateral movement until paracervical vascular plexus is seen and uterine artery is also at the level of the internal cervical os  
  • Identify an ascending or descending branch of the uterine arteries 
    • Narrow Doppler sampling gate (2 mm) 
    • Insonation angle <30 degrees 
    • Peak systolic velocity of a uterine artery should be greater than 60 cm/s 
    • PI measurement obtained when 3 identical waveforms are captured  
  • 95th percentile uterine artery mean PI (11-13 weeks) 
    • Transabdominal: 2.35  
    • Transvaginal 3.10 for CRL up to 65 mm 
  • Uterine artery PI may be affected by  
    • Ethnicity: African origin has higher PI 
    • Obesity: Decreasing PI with increasing BMI 
    • History of preeclampsia: Increased PI 

Note: Placental volume and vascularization indices are not recommended | Combined screening in the second trimester compares favorably to first trimester, but aspirin intervention is ineffective if initiated >20 weeks

Ultrasound Screening Only  

First Trimester Ultrasound Screening (10-13 weeks) 

• Due to maternal effects and lesser performance, uterine artery PI is not preferred as a stand-alone test based on cut-offs, but should preferably be incorporated into a combined, multifactorial screening model (see above) 
• Uterine artery PI >90th percentile in the first trimester detects  
  • 47.8% of women who will develop early PE (7.9% FPR) 
  • 26.4% of women who will develop any PE (6.6% FPR) 
• PI is superior to resistance index (RI) or uterine artery notching as a preeclampsia predictive tool 
  • PI is more stable than RI, and may still be used in cases of absent or reversed diastolic values 
  • Uterine artery notching is a subjective measure with low specificity
    • Associated with 22-fold increased risk for preeclampsia and 9-fold increased risk for an SGA neonate 
    • However, may be observed in up to 50% of patients at 11-13th weeks 

Second Trimester Ultrasound Screening  

• Uterine artery PI may be performed at time of the second trimester scan (10% FPR) 
  • 85% detection of early-onset preeclampsia  
  • 48% detection of late-onset preeclampsia  
• 95th percentile uterine artery mean PI (23 weeks) 
  • Transabdominal: 1.44  
  • Transvaginal: 1.58  

Third Trimester Ultrasound Screening  

• Use of PI during this period is not recommended due to insufficient outcomes data

Multifetal Pregnancies 

• Use twin-specific reference ranges  
  • Increased placental mass and lower mean uterine artery resistance seen in multiple gestation 
  • Combined screening approach 
    • >95% detection 
    • 75% screen positive rate

Learn More – Primary Sources:

ISUOG Practice Guidelines: role of ultrasound in screening for and follow up of pre-eclampsia