A scanner darkly?

With the 20 week scan fast approaching, exam results nerves are kicking in. Will it be ok? Will it have survived the incidents of accidental unpasteurised cheese eating? Did drinking at the wedding the weekend before I found out affect the baby? (In my defence, I had had a negative pregnancy test result so thought I was safe!). This is the big reveal (at least until the actual birth and you really know what’s what). Will we pass? And if we don’t, what on earth will we do?

I have been reading up on it – re-reading the Screening Tests leaflet from the NHS, reading all the articles I could find on the internet, and sending myself into floods of tears after reading the stories of those who made the decision no one should have to make.  I need to Think Positive, the odds are in our favour, 98% of babies are born without defects and there is no reason to believe we’ll be in the 2% beyond tendencies towards being Marvin the Paranoid Android. But still, I worry… And that hasn’t changed from the first time round!

Second Date Nerves

Just before the 12 week scan, sitting on the bus on the way to the hospital, I got nervous. Seriously nervous. Just like the days of collecting my exam results in school – full on adrenaline and a general feeling of dread. Fred tried to calm me down with helpful platitudes like “there’s nothing you can do about it now” and “everything will be fine”, but I was not convinced. I had prepared myself for the combined screening for Down’s or if the baby’s heartbeat was not longer there, but sitting on the bus I realised I hadn’t prepared myself for any other kind of problem they might find, like missing legs or arms – I suddenly realised they were also a possibility and it freaked me out.

We had had a 7 week scan due to my medical condition (they wanted to check the pregnancy was “viable” before putting me on expensive treatment). I had narrowly avoided a vaginal probe then and had the normal ultrasound via belly method – I think the look of horror I had given when the sonographer in the EPU (Early Pregnancy Unit) brought out the probe made her think it was worth trying the belly first, just in case! And there is was, our little blob, vibrating with its heartbeat but looking more like a peanut that a human being.

The 12 week scan is officially the dating scan, used to confirm your due date. But a number of other checks are done at the same time, specifically at least in my case:

  • Fetal heart activity
  • Crown Rump Length (CRL)
  • That the following appear normal: skull/brain, abdominal wall, stomach, hands, feet, amniotic fluid and the umbilical cord
  • Placenta position – fundal meaning it’s at the top of the uterus, anterior at the front, posterior at the back and praevia. Praevia means it is at the bottom and in some cases could be covering part or all of the cervix – this could lead to complications, but often by the 20 week scan it will have moved out of the way due to the uterus expanding
  • Nuchal Translucency (NT)

Given the state I had gotten myself into before the scan, I was extremely nervous going in.  I laughed with relief when the sonographer brought up the image of something now much more recognisably baby like (at least to us – my mother thought the picture of the scan looked like four blobs). It took a while for the sonographer to get all the measurements she needed but it gave us a chance to get to know the being growing inside me. It was moving about a lot (much to her annoyance) and at one point appeared to entirely arch its back – perhaps in protest to being prodded about. We got a bit worried about the legs as they seemed to us to be curving into the body rather than away as we would have expected, but she wasn’t worried about it at all – seems to be just the way they look at this stage. All was right with the world.

The Combined Test for Down’s Syndrome

If you have chosen to check for Down’s Syndrome (and Edwards’ Syndrome which is tested alongside) as we had, then the nuchal translucency test is one part, alongside your age and the blood test (to measure bHCG and PAPP-A) done on the same day that makes this a Combined Test. The nuchal transparency measures, in mm, the amount of fluid gathered under the skin at the back of the baby’s neck.

Essentially, this test is determining the risk level of a baby having Down’s Syndrome. Specifically, it’s looking for a high Nuchal Translucency, high bHCG and a low PAPP-A alongside an age-related risk which is higher the older you are. If you are interested in the science bit, this is an excellent summary and has some interesting graphs showing the expected range for NT against CRL and values of the bHCG and PAPP-A that were found to be associated with Down’s

A few week’s after the scan and the blood test, you will receive a letter with your results and a statement of your individual risk at term stated as 1 in x and whether that means you are low or high risk. If you are deemed high risk then you will be offered the diagnostic tests of CVS (chorionic villus sampling) or amniocentesis to tell you more definitively whether your baby has Down’s.

One thing that I didn’t recognise when going through this test was that the screening test results in a large number of false positives i.e. women who are given a high risk of Down’s Syndrome but whose babies do not have Down’s. Indeed a policy recommendations document I found stated that their target was “A detection rate (DR) of more than 90%, for a screen positive rate (SPR) of less than 2% (of affected pregnancies) for England for those undergoing combined screening”. What this means in practice is that they are aiming to detect 90% of cases of Down’s (meaning 10% will inaccurately get a low risk result from the combined test – the 1 in your 1 in x rating) and to minimise the overall percentage of those getting a positive screening result (the 2%). However, 2% is still a large number when you consider that as a percentage of the total number of pregnancies, and that means a lot of false negatives – indeed research from Barts hospital in London states that “among women in the screen-positive group, 1 woman will have a pregnancy with Down’s syndrome for every 9 who do not”.

So I guess the insight that gave me was that you shouldn’t panic if you get a “high risk” result, as the odds are still in your favour!  Although I know that that is very easy for me to say with our “low risk” result.

Just need to take a bit of my own advice when tackling the Anomaly Scan…

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