If your doctor has requested pre-eclampsia screening at your 12–14 week ultrasound, you may be wondering what it involves and why it matters. Here’s what the screening looks for, how your risk is calculated and what a result means for the rest of your pregnancy.
What is pre-eclampsia?
Pre-eclampsia is a complication of pregnancy that causes high blood pressure, along with other complications for the mother. It can also affect the baby, most commonly through growth restriction and premature birth. In severe cases, it can result in the loss of the baby during pregnancy.
Who is at risk?
Pre-eclampsia affects around 2–5% of pregnant women. Your risk is higher if you’ve had blood pressure problems before, but it can also develop in women considered low risk.
Severe pre-eclampsia before 34 weeks is far less common, affecting fewer than 1 in 200 pregnancies (0.5%). Because this early, severe form carries the greatest risk for mother and baby, it’s the main focus of first trimester screening.
How first trimester screening has evolved
The obstetricians at Ultrasound Care have been performing 12–14 week ultrasound screening for Down syndrome and other fetal abnormalities for the past 17 years. As research has grown, so has the scan’s complexity and its usefulness.
Until relatively recently, there was no way to screen for pre-eclampsia. Today, the 12–14 week scan can also identify women at increased risk of developing early-onset, severe pre-eclampsia. The screening program can detect around 90% of women who will go on to develop early-onset pre-eclampsia.
How your risk is calculated
Your individual risk is calculated by combining four pieces of information:
- Your history: your past medical history and family history
- Uterine artery blood flow: measured during your ultrasound examination
- Blood pressure: measured at your appointment
- First trimester blood test results: which can reflect how well the placenta is functioning
Together, these give a far more accurate picture than any single factor on its own.
Why early screening matters
The key advantage of screening at 12–14 weeks is that it leaves time to act. Starting low-dose aspirin early in pregnancy is thought to improve outcomes and reduce complications in about 50% of affected pregnancies.
If you screen positive and there’s no medical reason you shouldn’t take it, your doctor may advise low-dose aspirin (150mg) every night until 36 weeks of pregnancy. Always discuss this with your doctor before starting any medication.
What a high-risk result means
A high-risk result doesn’t mean you will develop pre-eclampsia. It means you’re likely to benefit from preventive treatment and closer monitoring as your pregnancy progresses.
Many women who screen as high risk go on to have healthy pregnancies, particularly with early care in place. Your doctor will talk you through your result and what it means for your antenatal care from here.