In order to identify the increased risk for certain birth defects during pregnancy multiple marker tests have become standard procedure. The birth defects detected include neural tube defects (NTDs), Down syndrome and trisomy 18.These tests are
However, it is important to note that multiple marker tests are only for screening the risk of stated birth defects. In order to confirm them, further tests are required to be done.
Sample – Blood sample
a. Alpha – Fetoprotein (AFP) – The fetus produces this protein called Alpha-fetoprotein. Lower levels of AFP indicte increased risk of Down syndrome and trisomy 18.
b. Estriol (uE3) – Fetus and placenta both produce this estrogen. Low levels of estriolindicateDown syndrome and trisomy 18.
c. Human Chorionic Gonadotropin (Total Beta-hCG: ThCG) – Human chorionic gonadotropin is a hormone produced within the placenta. High levels of hCG Down syndrome, while lower levels may be seen in trisomy 18.
d. Inhibin A – It is a protein produced by the placenta and ovaries. Increased total InhibinA levels are associated with Down syndrome, while decreased levels may be seen in trisomy 18.
Advantage compared to triple marker test: There is greater chance of identifying pregnancies at risk for Down Syndromewith the evaluation of Inhibin-A levels. The false positive rate of the test is also lower.
Markers tested here are – Alpha-Fetoprotein (AFP), Estriol (uE3) and Human Chorionic Gonadotropin.
Markers tested here are –
a. Serum free β-human chorionicgonadotrophin (free β-hCG) – Its high levels indicate risk for Down syndrome and in low level for Trisomy 18 and 21.
b. Pregnancy associated plasma protein A (PAPP-A) – Its low levels are found not only in trisomy 21, trisomy 18 and trisomy 13, but also in non-Down syndrome.