A blood sample taken between 14 and 22 weeks of pregnancy (the earliest time to screen for open neural tube defects is 15 weeks) is analysed for four hormones in the blood. These are alpha-feto protein, free estriol, free bHCG and inhibin-A. The stage of pregnancy is most accurately determined by ultrasound. The levels of the four hormones in the blood are compared with the mean (MoM=Multiple of median) values of the same hormone results of pregnant women in the same week.
The concentrations of these four substances are analysed by a computer using a mathematical formulation with factors such as age and race, smoking and/or alcohol use and previous miscarriage, Down’s syndrome history in the family, and the result is given as a probability estimate.
Interpretation:In Down’s syndrome pregnancies, AFP and uE3 levels tend to decrease, while free ß-hCG and Inhibin A levels tend to increase. The AFP level is also used to determine an increased risk of open spina bifida or anencephaly. The doctor should make the interpretation.
Sample: Arm venous blood. Nonfasting
Working day: Everyday
Result Time: 2 days at 6 PM
