what does the first trimester (10 week) blood test actually test for?

[tenar]

I just had a blood test today, the one that they combine with the ultrasound in a couple of weeks to give a risk assessment for downs syndrome etc.

But I was wondering what they actually measure in my blood that can indicate the chances of a problem with my baby. I would have thought that since my blood and the baby's blood aren't connected, there wouldn't be any information in mine that would be useful to tell about the baby. Can anyone tell me more detail about it? I'm not worried about it, just curious.

Thanks!

[Alan]

Hi Tenar
The main tests are
Blood Group (A, B, AB, O)
Rhesus factor (Pos or Neg)
Haemoglobin (often called iron levels)
Rubella
They will also often test for
Syphillis
Hepatitis C
Aids

[tenar]

Hi Alan,

Thanks for that, I understand all of those ones.

So how does the blood test help them to predict my chances of a baby with downs syndrome? Because they do use it for that, don't they, or have I misunderstood that part?

[Alan]

The blood test you are talking about is called “Maternal serum screening”. This test measurers some chemicals in your blood. It is used together with an ultrasound (nuchal translucency scan ) that measurers the skin fold at the back of the baby’s neck . Another thing that is considered is the age of the mother. These results are then considered together and from this they can work out the chance that this baby has downs syndrome.

[Snacks]

From what I have read, tenar, if they find that an abnormality shown in the scan (i.e. increased nuchal thickness) and that corresponds with your blood test showing a higher HCG level and lower PAPP-A level, then Down's is more likely.
Google Nuchal Translucency and see what you find I'm sure there's more to it than that, but that's my limited understanding of it.

[tenar]

Thanks both, for that information. I like to understand these things.

[HotI]

Hi Tenar

The first trimester serum screening test measures the concentrations of two substances in the blood: human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein A (PAPP-A).

By combining the results of the serum screening test (10 week blood test) with the Nuchal Translucency measurement (12 week ultrasound) and the Mother's age and weight, a 'risk figure' can be given that your bub has Down syndrome (Trisomy 21) or Edward syndrome (Trisomy 18).

A change in the levels of these two proteins (hCG and PAPP-A) may indicate a higher chance of the baby having Down syndrome, or Edward syndrome.

The NT scan involves measuring the amount of fluid behind the baby's neck. An increased NT measurement can indicate that the baby has a chromosomal variation such as Down syndrome.

[HotI]

Pregnancy-associated plasma protein-A (PAPP-A) largest of the pregnancy associated proteins produced by both embryo and placenta ( syncytiocytotrophoblasts) during pregnancy (Placenta Notes). This protein is thought to have several different functions, including preventing recognition of the fetus by the maternal immune system, matrix mineralization and angiogenesis. Levels of PAPP-A rise from first detection in the first trimester until term.

Maternal serum concentrations are related to subsequent fetal growth and this relationship has suggested that it can be used as a diagnostic test for adverse pregnancy outcomes (intrauterine growth restriction, premature birth, preeclampsia, and stillbirth).

(taken from the University NSW Embrology website)

Human chorionic gonadotropin (hCG) is a hormone produced in pregnancy that is made by the embryo soon after conception and later by the syncytiotrophoblast (part of the placenta). Its role is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain progesterone production that is critical for a pregnancy in humans. hCG may have additional functions; for instance, it is thought that hCG affects the immune tolerance of the pregnancy. Early pregnancy testing, in general, is based on the detection or measurement of hCG. Because hCG is produced also by some kinds of tumor, hCG is an important tumor marker, but it is not known whether this production is a contributing cause or an effect of tumorigenesis.

(taken from Wikopedia)

Both proteins have 'normal' function during the pregnancy. I don't think they have fully worked out why the altered levels occur more often in pregnancies when the bub has down syndrome. Or why the levels can be altered when the bub does not have down syndrome.

They have just worked out that by combining the results of all these different screening tests (serum/NT scan/age) they can more accurately calculate the probability so that parents have more info and they can then consider whether they want to have more invasive tests to give a definitive answer to whether the bub has a chromosomal variation.

I think it is great that you are asking the questions.

[tenar]

Thanks very much for all the details, Kate, that is exactly the sort of information I was after. I appreciate you taking the time to post it.