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Pre-Eclampsia Screening 11-14 weeks scan 

Pre-eclampsia is a condition where irregular placental development causes the mother’s blood pressure to rise after 20 weeks of pregnancy and affects the mother’s kidneys resulting in protein being lost in the urine. It is associated with abnormal placental function, fetal growth restriction and prematurity. Pre-eclampsia affects 2-5% of pregnant women, of whom about 1 in 200 (0.5%) will have a severe form of the disorder arising early and requiring delivery of the baby before 34 weeks gestation. (Jon Hyett: Fetal Medicine, 2013

The “12 week scan” performed at Paradise Ultrasound now identifies women at an increased risk of evolving early onset, severe pre-eclampsia on the basis of a combination of past or family history of hypertension, biophysical parameters (BMI and mean arterial blood pressure), first trimester sonographic features (Uterine artery Doppler assessment) and maternal serum markers of placental function (PAPP-A +/- placental growth factor). Combination of these parameters in a validated risk algorithm (Fetal Medicine Foundation, London) allows identification in the first trimester of approximately 90% of those women destined to develop pre-eclampsia prior to 34 weeks, with a false positive rate of 10%.

The pre-eclampsia screening process does not require extra blood tests however it requires additional time with your normal first trimester screening. Pre-eclampsia needs to be requested by your referring doctor, and it is necessary to tell the receptionist at Paradise Ultrasound when booking the appointment as this appointment will take at least an hour.

At this scan you will be asked some questions relating to your health and your family, as a family or personal history of high blood pressure will affect your risk estimate. This information will be combined with ultrasound measurements of blood flow in the arteries supplying your uterus, your height, weight and blood pressure, and some information from the blood test used in screening your pregnancy for chromosome abnormality (the PAPP-A level). Using this approach, we can identify approximately 90% of women destined to develop early-onset pre-eclampsia.

Early screening for pre-eclampsia is important because early intervention (before 16 weeks gestation) can reduce the adverse effects for both mother and baby by over 50%.  This intervention involves taking a low-dose aspirin tablet (100mg, which is one-third the dose of a normal tablet) on a daily basis until 34 weeks.  The preventative effect is not seen if the aspirin is commenced after 16 weeks, as the placental changes have already become established by then. Aspirin is a very safe drug in pregnancy, and can be used by all women other than those who are allergic to this medication or have a stomach ulcer.

Like all screening tests, pre-eclampsia risk assessment is not 100% accurate. Approximately 90% of women who develop early and severe pre-eclampsia will be correctly identified as high risk by the combined test. About 5-10% of women will be considered at high risk but will not develop the condition (this is called a false-positive risk result). These women will still be offered the aspirin intervention and will be monitored a little more closely during the pregnancy. They may develop pre-eclampsia later in the pregnancy but it is usually of a much milder form that has fewer adverse effects for both mother and baby.

The results of the pre-eclampsia screening test will be forwarded to your doctor and you should discuss the treatment and monitoring issues with them. Each woman has different family and personal health factors that contribute to the pregnancy management, and your obstetrician (private or hospital) is best placed to individualize your care.

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