Lab Update 13 – First Trimester Pre-eclampsia Screening

Revised: November 2020
Dr René van der Watt, Chemical Pathologist
Ampath | ampath.co.za

What is Pre-eclampsia (PE)?

Pre-eclampsia is a significant cause of maternal and neonatal illness and death, particularly when it presents early (delivery before 34 weeks).

Complications include:

• Intracranial haemorrhage
• HELLP syndrome
• Eclampsia
• Pulmonary oedema
• Renal failure
• Abruption of the placenta
• Foetal growth restriction
• Intrauterine foetal death
• Preterm birth

Long-term maternal risks:

• Cardiovascular disease
• Cerebrovascular disease
• Renal disease

Long-term risks to offspring:

• Hypertension
• Coronary artery disease
• Insulin resistance

In South Africa, PE prevalence is:

• 5.75% for all PE
• 1.43% for severe PE
  Globally: 2–5%

Why Screen for PE in the First Trimester?

All pregnancies should be screened for preterm PE between 11w0d and 13w6d, as recommended by the International Federation of Gynecology and Obstetrics (FIGO). Early identification allows timely prevention using low-dose aspirin.

Key points:

• Aspirin must be started before 16 weeks to prevent PE.
• Screening combines maternal risk factors and biomarkers.

What Does Ampath Offer?

Ampath Esoteric Sciences provides first-trimester PE screening for both singleton and twin pregnancies.

Risk calculation uses Alpha software based on:

• Maternal parameters:
  • Parity
  • Previous PE
  • Family history of PE
  • Weight
  • Ethnicity
• Biochemical markers:
  • PAPP-A (Pregnancy-Associated Plasma Protein A)
  • PLGF (Placental Growth Factor)
  Both are decreased in pregnancies that develop PE.
• Clinical parameters:
  • Uterine Artery Pulsatility Index (UtAPI)
  • Mean Arterial Pressure (MAP)

For MAP:

• Patient must sit for 5 minutes with arm supported at heart level.
• Use appropriately sized cuff.
• Measure BP twice, one minute apart.
• Submit the average of the two readings.
• MAP is calculated as:
  MAP = Diastolic BP + (Systolic BP - Diastolic BP)/3

Alpha software accepts either MAP or individual systolic/diastolic values.

Screening Effectiveness

• Using maternal factors alone:
  • 63% detection rate
  • 19% false positive rate
• Using maternal factors + biomarkers (PLGF, PAPP-A, MAP, UtAPI):
  • 94% detection rate
  • 15% false positive rate
  • At a risk cut-off of 1:100

Benefits of PE Screening

• Detects high-risk patients as early as 11–13 weeks, before clinical symptoms start (>20 weeks)
• Allows early intervention and closer monitoring
• Enables referral to appropriate care
• Prevents PE with low-dose aspirin (~150 mg/day) starting at 11–14 weeks until 36 weeks or diagnosisASPRE trial shows:
  • ~90% reduction in early PE (<32 weeks)
  • ~60% reduction in preterm PE (<37 weeks)
• Enables antihypertensive treatment if BP rises
• Ensures tight BP control in chronic hypertensive patients

Antenatal Screening Timeline and Options

If first visit is at 8w–9w6d gestation:

1. Collect blood for FTDS (Down screening)
   • Best detection if collected before 10 weeks
2. Collect blood again at 11w–13w6d for FTPS (PE screening)
3. Collect blood at 16w–18w for NTD screening
   • Acceptable window: 14w–22w6d

If first visit is at 10w–10w6d:

• Wait and refer for blood draw at 11w–13w6d

If first visit is at 11w–13w6d:

1. Collect blood for FTDPS (combined Down and PE screen)
   • Submit NT (nuchal translucency) measurement
   • PLGF improves Down’s detection
2. Collect blood at 16w–18w for NTD

If first visit is at 14w–15w6d:

• Refer for blood draw at 16w–18w for NTD or STDS

If first visit is at 16w–22w6d:

1. Collect blood for STDS (Second Trimester Down Screening)
   • Acceptable window: 14w–22w6d

Test Mnemonics, Timing and Analytes

• FTDPS
  • Conditions: Down syndrome, Trisomy 18/13, PE
  • Requirements: NT measurement
  • Timing: 11w–13w6d
  • Analytes: fBhCG, PAPP-A, PLGF
• FTPS
  • Condition: PE only
  • Timing: 11w–13w6d
  • Analytes: PAPP-A, PLGF
• FTDS (Biochemistry-only)
  • Condition: Down syndrome, Trisomy 18/13
  • No NT required
  • Timing: 8w–13w6d
  • Analytes: fBhCG, PAPP-A
• FTDS (Combined risk with NT)
  • Condition: Down syndrome, Trisomy 18/13
  • Timing: 10w6d–13w6d
  • Analytes: fBhCG, PAPP-A
• FTDS2
  • Condition: Down syndrome, Trisomy 18/13
  • NT required
  • No additional blood needed if already drawn
  • Timing: 10w6d–13w6d
• STDS
  • Conditions: Down syndrome, Trisomy 18, NTD
  • Timing: 16w–18w ideally (acceptable: 14w–22w6d)
  • Analytes: HCG, E3, AFP
• NTD
  • Condition: Neural Tube Defects
  • Timing: 16w–18w ideally (acceptable: 14w–22w6d)
  • Analyte: AFP

📌 For more information, please contact your local Ampath pathologist or visit www.ampath.co.za