I’m in the very unhappy position of having recently received a very high risk outcome from the NHS antenatal combined screening – 1:2 risk of Down’s Syndrome (Trisomy 21) and 1:40 for Edwards (Trisomy 18) and Patau (Trisomy 13) - and after a CVS was not possible I'm waiting for an amniocentesis after I was advised that it would be better to give a clear result. My local NHS Trust does not allow for invasive testing if a low risk result has been given by the NIPT and I was told that in some cases when you have been given a very high risk outcome from the combined screening you can be given a false negative. I'm not sure if that is the advice others have been given and I don't want that to contradict what you have been told. Given such a high risk outcome it makes sense to me to have the invasive test done, as ever these are personal decisions based on personal circumstances.
I have never posted on Mumsnet before, but as with many posters in this category I have found it a source of information since finding myself in this position (I think I've read almost every relevant thread) and I wanted to give something back and share what I had found out from reading up on the different elements of the screening to explain what they are and what might constitute a high or low result. I have used medical (NHS or other health systems) or scientific (published articles in journals) websites in sourcing this information. I want to preface my sharing by saying I am not from a medical background, nor am I particularly scientifically minded so trying to wrap my head around this has been a challenge but if collecting this information in one place helps one person who is in my situation then I would consider it worthwhile. This is such an overwhelming and traumatic time that going down a Google black hole can just add to the anxiety.
How the risk score is calculated
There are certain indicators that looked at together can predict whether an individual is at higher risk of having a baby with chromosomal and/or health problems. These fall into 3 categories:
Biochemical Markers – These are proteins in the blood: PAPP-A and β-hCG. You are given a blood test to determine their levels. In antenatal screening the measured concentration of the markers is converted into something known as a Multiple of Median (MoM) which is a measure of how far an individual test result deviates from the median (middle) value of a number of tests. The average adjusted value in a ‘normal’ pregnancy is 1.0 MoM at all gestations so you’ll see people saying that you’d want both of your scores to be near to 1.0 but I think this simplifies the situation a bit (see detail under the other headings).
Ultrasound Markers – Nuchal Translucency is the major indicator used in the NHS. There are also other soft markers that your NHS Trust might review at your dating ultrasound although it seems that review of these varies across the country. These soft markers are usually the presence or absence of a fetal nasal bone and ductus venosus waveform which is looking at the blood flow from the umbilical cord to the baby.
Clinical Factors -
These include the Maternal Age (age of mother at the time of expected date of delivery); Ethnicity; whether you have Insulin Dependent Diabetes; whether it is an IVF pregnancy; number of foetuses present; weight of mother; smoker status.
The clinical factors produce a priori risk which is multiplied by a likelihood ratio calculated from the ultrasound findings (specifically the NT measurement) and the biochemical markers (blood test results) to give a patient specific risk score of 1 in x number likelihood. A definition of a high risk result which would lead to an offer of further investigation in the NHS is a result greater than 1:150.
Nuchal Translucency (NT)
The sonographer takes a measurement of the collection of fluid under the skin behind the neck/at the back of the neck (also known as the nuchal fold) of the baby. This measurement should be taken between 11 and 14 weeks of pregnancy – before 11 weeks the baby is too small and after 14 weeks the excess fluid may be absorbed by your baby, and the visibility of this fluid reduces on the ultrasound so is no longer an accurate indicator.
A higher measurement can be a normal variation, or it can be an indicator of a chromosomal abnormality or a heart problem. An increased NT happens in approximately 1 in 150 pregnancies.
It is commonly suggested that a reading above 3.5mm is considered high. Looking into this a bit more I’ve discovered that the NT measurement increases with the gestational age of the baby, so a larger measurement if you are closer to 14 weeks than 12 is normal. Around 11 weeks the NT measurement would be expected to be less than 2mm, at 12 weeks less than 2.5mm, at 13 weeks less than 2.8mm. If your baby’s Crown to Rump Length (CRL) is between 45-84mm the NT measurement before 13w + 6 days would usually be less than 3.5mm.
If your NT measurement is below 1.3mm your risk for DS would be considered very low. If it’s above 3mm it would be considered a risk of DS and if was above 6mm it would be a high risk of DS and some other birth defects.
PAPP-A (Pregnancy Associated Plasma Protein-A)
To simplify this is a protein that is produced by the placenta that is needed for the implantation process and to maintain a healthy placenta. A low level of PAPP-A is an indicator of Down Syndrome, Edwards and Patau. It can suggest abnormal placental function which impacts on the growth and birth weight of your baby. Low PAPP-A may also mean increased likelihood of pre-term birth and pre-eclampsia in the third trimester. There is nothing you can take to increase your PAPP-A levels, but you are recommended to take aspirin to reduce certain risks (like that of preeclampsia) and with extra care and support if needed (like additional growth scans in the third trimester) most pregnancies with low PAPP-A levels will result in the birth of healthy babies.
From what I could establish anything under 0.4 MOM is considered low.
β-hCG (human Chorionic Gonadotropin)
This is a hormone normally found in blood and urine only during pregnancy. Elevated levels of hCG have been found to be an indicator of DS.
From what I could establish anything less than 0.5 MoM is considered low, anything over 0.5 MOM but under 2.0 MOM is considered normal, and anything over 2.0 MOM is considered high. Having low or high levels are associated with increased risk of adverse pregnancy outcomes.
Combinations of results
Increased maternal age increases the risk for all pregnancies.
In pregnancies with Down’s Syndrome: PAPP-A tends to be low, NT and hCG tend to be raised.
In pregnancies with Edwards and Patau: PAPP-A and hCG tend to be low; NT tends to be raised.
I'm currently holding on to any little bit of hope I can muster that the amnio will give us a positive outcome. My age (43) drives the risk factor up, my NT measurement was elevated although below 3.5mm (the sonographer struggled to take measurements as the baby was moving so much so unsure how accurate this reading was), my PAPP-A was low, my hCG was slightly above 1.0 MOM. All of these things coming together clearly has made me high risk although I was not when I had my son at 42. Wishing anyone in a similar position lots of good luck for a positive outcome, and for a happy and healthy pregnancy.
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Antenatal tests
Info for those with a high risk screening result
15 replies
Hopeisneeded · 09/11/2023 17:56
OP posts:
MrsScotland ·
10/11/2023 12:02
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linz1987 ·
27/02/2024 22:50
HannahPom5 · 27/02/2024 21:34
Hi everyone,
It's been really helpful reading all these posts.
I had the call today that I am high risk for downs syndrome (1 in 29).
My HCG is 3.8 (considered high)
PAP A is 0.3 (considered low)
NT is 1.6mm (I think this is considered normal)
I'm 36 and this is my first pregnancy. I'm planning on calling ARC tomorrow and then most likely booking the NIPT blood test.
Has anyone else had similar results? It was a whirlwind of information on the phone call.
Does the NIPT give results as 'high' or 'low' or is it more specific? From what I read it sounds more specific but the midwife just said high/low.
I hope everyone is doing OK.
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