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