The FTS must be performed between 11+ weeks to 13 weeks 6 days gestation, best around 12 weeks. This is performed via:
1. History
2. Physical examination of height, weight and blood pressure measurements x 2 on both sides
3. High resolution ultrasound scan of:
Length of fetus
Nuchal translucency (NT) - fluid behind the neck of the fetus
Soft markers e.g. nasal bone (NB)
Obvious structural abnormalities
Doppler studies of the blood flow to both sides of the arteries to the uterus
4. Blood tests
Different combinations of mother's blood for free bhCG and PAPP-A between 8-13 weeks gestation and / or placental growth factor (PlGF) during 11-13 weeks can be chosen for this test.
Free bhCG and PAPP-A improve the detection rate of Trisomies 21/18/13 and hence may not be necessary if the more accurate non-invasive prenatal test (NIPT) is already being done for the screening of Trisomies 21/18/13.
PlGF, on the other hand, is useful to increase the detection rate of preterm pre-eclampsia (which is a condition of high blood pressure associated with proteins in the urine during pregnancy) and fetal growth restriction (which is a condition in which the fetus is growth restricted) requiring preterm delivery. As the level of PlGF is low in pregnancies with Trisomies 21/18/13, a low PlGF may also increase the risk of Trisomies 21/18/13.
It is designed to screen for 4 groups of problems in pregnancy:
a) Risks of common chromosomal abnormalities (including Down syndrome [Trisomy 21], Edward syndrome [Trisomy 18] and Patau syndrome [Trisomy 13]) using Fetal Medicine Foundation (FMF) software. This allows the detection of 90% of Down syndrome, 90% of Edward syndrome and 90% of Patau syndrome.
b) Early structural abnormalities such as anencephaly (absence of skull), exomphalos (protrusion of intestines through an abdominal wall defect), megacystis (enlarged bladder), etc.
c) Risk of early pre-eclampsia requiring delivery < 37 weeks (i.e. a serious condition during pregnancy characterised by high blood pressure with proteins in the urine). If left untreated, pre-eclampsia tends to progress and may become very serious. As the treatment of pre-eclampsia is delivery, we are most worried if the pre-eclampsia occurs early (i.e. before 37 weeks) which may require us to delivery early. If the risk of pre-eclampsia is raised, calcium supplementation of at least 1.5-2 g / day and low dose aspirin of 150 mg taken in the night reduce the risk of this complication. Low dose aspirin reduces this risk by 70% while calcium supplementation of at least 1 g / day may reduce this risk by 50%.
d) Risk of fetal growth restriction before 37 weeks which may require early delivery. If fetal growth restriction is detection, the fetus needs to be closely monitored with fetal movement chart, regular measurements of the fetus and regular Doppler studies of the blood flow within the baby, and also cardiotocography (CTG) later in the third trimester. When the fetal status is non-reassuring, early delivery may be indicated. Low dose aspirin of 150 mg taken in the night and calcium supplementation of at least 1.5-2 g / day may reduce the risk of fetal growth restriction. However, low dose aspirin may reduce the risk of fetal growth restriction by 30%.
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