Is Genetic testing on cord blood reliable for trisomies?

[lcoc2015]

We had the Harmony prenatal testing done before 12 weeks. The results gave a 33% chance of of Triple X or TrisomyX.

We decided not to have an amnio but wait for the birth where the cord blood was sent for genetic testing (karyotyping). We got results today to say that they were chromasomally normal which is fantastic but the doctor said to be absolutely sure we'd need to do a further blood test on the baby.

I cannot face much more stress in terms of testing and waiting on results. Does anyone know how reliable the karyotype tests on the cord blood are? I.e. how likely is it that we have a false negative?

Cord blood is the babies blood, so I would have thought it was pretty damn reliable.

Hope everything turns out ok for you.

I hope so dropyoursword! I am not medical but was reading about it today. From what i read the umbilical cord carries deoxygenated blood away from the foetus and carries oxygenated blood from the mother to the foetus. To me that sounds that both maternal and fetal blood is in the cord but as i said i could have this utterly arseways! Would love anyone who knows for sure to shed some light!

No, both the umbilical vein and arteries all just carry fetal blood. Nutrients and oxygen etc that is carried by maternal blood is 'dropped off' and converted via the placenta. So definitely no maternal blood in the cord. I wonder if there is the slight chance of maternal blood being on the surface of the cord which could affect the result, but would think this would be very very unlikely to give you a false negative.

Thats very reassuring DropYourSword - thank you so much. You obviously know your stuff!! The baby shows zero phyaical aigns of the trisomy x. That, with the cord blood results then is enough for me unless she shows developmemtal delays later on.

My experience of babies with a trisomy is that there are physical indicators once the baby is born. Has anyone talked to you about partial or mosaic trisomy?

No hoping the test was specifically for Triple x syndrome which can have no physical markers (it can have some like epicanthsl folds, crossed little finger and crease on palm but many girls with Triple x dont have these physical features).

Was the blood tested for all genetic issues ? It sounds like it was a micro array which take the genetics of the baby and checks it against a normal set . The reason why I say this is I have a child with a undiagnosed genetic condition . Nothing was picked up antenatally ( apart from shortish femer but within normal ranges ) . We had a cvs and it came back normal but it was 5 years ago and the test wasn't available then . I didn't know they could see epicanthal folds in utero . My son has them and they weren't picked up .