ANYONE SEE THAT SEX TEST AT 6W PG ARTICLE?

[lissielou]

t'was in the sun but theres an over the counter test you can get called pink or blue (or similar) and from a prick of mums blood you can tell what sex the 6w foetus is.

jd, that was the point i was making earlier on, having had multiple mcs at around 6w (1 earlier, 1 later) i would have been devestated to have known whether id lost a ds or dd.

jdd0709 - certainly there have been methods of extracting fetal DNA from maternal blood which would have been confused by the presence of DNA from previous pregnancies. The test used now (free fetal DNA) is based on DNA which is present in maternal blood during that pregnancy only, and which degrades very quickly so it is hardly present at all only a few hours after the birth.
This testing has been used clinically in the UK for the last couple of years for families with rare inherited disorders where the affect on the fetus depends on whether it is male or female (females are affected, males not so). Previously the doctors had to treat all pregnancies as if they were female until proven otherwise, which meant the mum having to take medication for all pgs. Now they can use fetal DNA to detect the males and the mums only need to take the medication if they are carrying a girl - however...the sex is always (in my experience) checked by a CVS at 12 weeks to make sure.

The report I read said that if the test got the sex wrong you would 'get your money back' ..now since they are 50% likely to get the answer right, it's not a great gamble for the company, but still would n't compensate for all those pink clothes and nurseries that need repainting.
From what I understand, in the UK, most of the 'not telling you the gender at 20 week scan' (which happens at some hospitals) is more to do with not wanting to get sued for someone for their purchasing of gender-specific clothing rather than the fear of them terminating a female pregnancy.

Private karyotyping for sex selection reasons (via cvs or amnio) has been happening in many countries for years, in some ways, at least having access to an earlier gender test will mean that the terminations will be carried out an an earlier gestation.

Can you explain that more Millarkie? They say that they are detecting DNA from fetal cells that are being broken down in the maternal cicrulation, but they also imply that they are using PCR. How on earth would that not detect Y chromsomal material from previous pregnancies? I just don't get how it differs from previous methods unless they have some way of specifically sorting cells undergoing apoptosis, but that doesn't sound very likely, and wouldn't be foolproof anyway.

I'll have to get my notes from work tomorrow Tamum - haven't any info in the house.

Couldn't you 'simply' use a gradient to separate the cells and the much much tinier cell-free DNA? (much like the way you would separate baterial DNA+bacterial coat from plasmid DNA (probably showing my age by that ) - I'm trying to restrain myself from pubmed on a bank holiday

Tamum - If you have time, try Prenat Diagn. 2006 Jul;26(7):598-603.

Oh hello I'm sure you could use a gradient, it's just that they say on the website that they use blood spots and I would have thought it would be a bit challenging to do a gradient from that. Interesting. Thanks for the reference, I'll have a look!

Oooh, blood spots - (hadn't looked at the website) - not so easy to choose the origins of your DNA from! well as I said previously - they've got a 50% chance of getting it right through chance alone .

sounds suspect to me if they are using PCR - and if the free DNA only persists for hours doesnt that mean that if you dont take the sample within that window you would miss it and hence possibly get a false negative for a boy?

The free fetal DNA is not present in the maternal blood a few hours after the birth - it is in the maternal blood and thus in any blood sample taken, during pregnancy - it does not follow that the DNA in the sample will degrade just as quickly as that in the body.
And if they are doing things properly they will not just be PCRing markers on the Y chromosome, but also markers which are present on both X and Y in order to determine the number of sex chromosomes present and the existance of a single or 2 X chromosomes (ie. the absence of a PCR product would not mean fetus was female, unless it was confirmed by PCR products showing 2 X chromosomes and a 2 sex (either X or Y) chromosome result). e.g. If you use PCR to sex a fetus from CVS or amnio samples then multiple markers are used.

Ah, it all makes more sense now, thanks Millarkie. I hadn't realised that the fetal DNA was in such high concentrations in maternal plasma- betwen 3 and 6% apparently. That paper is all about plasma or serum though, and it sounds as though the company is using whole blood, so it's not quite the same. I did wonder if you had a fabulous method of doing gradients that separate cells and DNA from blood spots Millarkie (and yes, I am plenty old enoguh to remember that method for plasmids!)

Yes, can't explain the blood spot extraction. Would be interested in their method.