Down Syndrome Risks

Hi. My sister is 20 weeks pregnant. She is only 30, and decided against the NT scan, because she thought the risk was low as we have no history of DS in our family, or her partners family. She had her 20 week scan done yesterday, and the sonographer was worried about the neck measurements. The results came back today, showing she has a 1/300 risk of her baby girl having DS. THe Dr at the Gladstone hospital is sending her done here to Brisbane, and they are rushing her to get another scan done on this Tuesday. If the risk goes down to 1/100 she said her Dr said that was bad. She doesn't really want an amniosyntesis, and she said it doesn't matter if the bub does have DS, she won't be terminating anyway. This is her 5th child, and she is really worried.

The question is, does anybody know the difference between the risks at 13 weeks (with the NT scan) and the risks at the 20 week scan? Because I have heard and read in here that the risks are generally good even if its 1/300 or 1/100. Any help/advice would be much appreciated?

You can't have a NT scan at 20 weeks, they can however identify soft markers for DS that can indicate DS, but they are only indicators and can be normal variants.

If your sister is not going to terminate regardless, then maybe the risk of an amnio isn't worth it? Although some people like to know for sure to help them prepare psychologically...

Sorry to hear she is going through all this, hope all goes well.

When I had my 12 week NT scan I was told the cut off between high and low risk was approx. 1/300. They didn't have a moderate risk category. I don't know the process for detecting risk of DS in the second tri scan. My score was about 1/400 at 12 weeks which I had mixed feelings about, even though I was technically in the low risk I still felt at a moderate risk. IMO 1/300 is still a long shot of having DS. It could happen to any of us as the scans can't detect with absolute certainty.

I agree with Jungle Mum that an amnio could give more information in case she's thinking of terminating but it could also give some psychological reassurance or help to prepare. She probably should ask the risks of having an amnio as the risks might outweigh the benefits.

Thanks Junglemum. I know you can't have an NT scan at 20 weeks. I was talking about the morphology scan. They have measured the fold somewhere in the neck, and apparently the baby's fold is 6mm, and that is borderline. So, I'm just trying to see if the risks that the sonographer/Dr give you are the same at the 13 weeks NT scan as the morpholoy scan.

She deffinately isn't terminating. So I'm asking her if she is having the amnio, but I'm thinking she will wait and see how the next more in depth scan goes. Then once she gets the info/risks of the amnio, I guess she will decide from there.

if it were me, termination wouldnt be an option either, but id still get the amnio done to be prepared and do research b4 the baby was born. fingers crossed all is well xxx

The measurement of the fold is called the nuchal measurement and its size at 20 weeks is not relevant to DS. The measurement is only useful as an indicator of DS at the 12 week scan, it is a very specific time frame. After this time it is not at all an accurate indicator of DS. It *can* be a soft marker at 20 weeks and that combined with other soft markers may warrant further investigation, but it's not as strong an indicator as when done at 12weeks.

I'm not very good at explaining myself sometimes! Sorry.

A second opinion u/s is a good idea. I have had friends with similar stories and it was a false alarm each time. Second opinions are always warranted. :hug:

That's ok junglemum. Thanks ok. I wasn't sure if I had explained myself properly. But thank you for the advice. :)

Her calculated risk is 1 in 300. So out of 300 women with the same marker/measurements there will be 1 woman who has a baby with down syndrome. Risk is all relative. Some people consider 1/300 to be 'high risk', others would not be concerned at this value.

The only reason that medically they use 1 in 300 as the high/low risk cut-off is you are weighing it up against the risk of losing the pregnancy following diagnostic testing (CVS or amnio). CVS has a stated pregnancy loss risk of 1 in 200 and for amnio it is 1/100.

In her follow up scan, they may carefully check for other markers than can indicate the bub has down syndrome. The more markers, the higher the probabilty that the bub does have DS, but some bubs who don't have DS also have these markers.

Thanks Kate. She's just really worried even tho I've told her it'll most likely be ok. She is coming to Brisbane to have another scan because they don't do it where she is. It's alot of expense for her. But like I said, I'm sure it'll be ok :)

I didn't have the 12 scan with either of my boys, but was told at my 20 week scan with DS2 that I had 3 soft markers and 1 hard marker (short humerous). Together these gave me a risk of 1/20. I had a second opinion scan a week later and they found only 1 of the soft markers (which was very mild) and the humerous length was normal. My risk was back out to 1/600. DS2 was born without any problems.

Please tell your sister not to worry until she has had the second opinion scan, easier said than done, I know. I assume that if she is coming all the way to Brisbane then she will be going into QLD Ultrasound for Women? They are fantastic in there... spend ages doing the scan and they have genetic counsellors who speak to you about your risks and what they mean etc.

As the other posters have said, the NT measurement is not very reliable at 20 weeks. They are called soft markers for a reason, and if that is her only marker (you didn't mention any others), then it probably means nothing.

She is going to the Royal Womens hospital. All she said to me was they were worried about the neck measurements and apparently the arms and legs are all good length. But I guess the Dr is trying to be thorough.

It is always worth a second opinion, especially where they have better facilities and equipment, and possibly experience. I am sure they are brilliant in at the Royal too. :)
I hope it all turns out OK for her.

Hi. Unfortunatly, I can't help you too much on the Downs side of the situation , but I would like to warn you that I've found at the Women's they can be extremely pushy about amnios. If she decides not to go for it, she needs to stand firm. Best of luck!!

Thanks charlotte. I will let her know.