Nuchal/dating scans - what to believe?

[NQWWW]

As the appointment I was given by my hospital for my dating/nuchal scan was quite late (at 13 weeks and 1 day), I booked a private one for 12 weeks. As it happens, the private one was delayed, so in the end there were only 5 days between the scans.

The private one confirmed my dates exactly, and gave me a risk factor of 1:1243. The NHS one says my due date is 5 days earlier, and my risk factor is 1:733. Both good risk factors for my age (I'm 37) but I'm surprised at the differences, and I've even started to wonder how much you can erly on these things at all, if they can give such different results.

Anyone else got any experience of this?

[Tinker]

SoupDragon is better at explianing this but I think one (the nuchal fold one) is the risk of the BABY having Downs the other (the NHS one) is the risk of YOU having a Downs baby.

[bundle]

NQWWW ultrasound machines vary quite a lot - that's why they write on your notes who the operator was and which machine you were measured on. I agree both numbers are encouraging for your age (same as me!) but IKWYM about the variance seeming quite large!

[NQWWW]

Tinker - they were both nuchal scans.

Bundle - in some ways what worries me more is that they've adjusted my due date. I'm sure of my LMP date and my cycle is very regular, so a five day adjustment is quite a lot. NB it would have been 6 days, but that put me at 14 weeks, and so too late to have the nuchal scan - when I started to cry at this news (pure frustration with a system that gives you an appointment for a test so late that it can cause this to happen) they adjusted it slightly to make me 13 weeks 6 days instead.

I keep thinking that if I go past my EDD, they will be wanting to induce me 5 days before they would have otherwise.

[Cha]

NQWWW - don't worry about the inducing so much. They can't 'make' you have an inducement - they just suggest it. If you really don't want to be induced when the time comes, be firm about it. They can scan the baby every day to see that it is all right if you / they have concerns and you all wait til nature takes its course. This happened to a friend of mine and she was adament she didn't want to be induced. She went to almost 43 weeks before her fine bouncing baby girl arrived. I personally was 12 days overdue and would have welcomed inducing, I was that impatient to see my baby! However, with this one, now I know what to expect, I will just hang on till s/he wants to meet us all.

[bundle]

My dd was 40 weeks +13 days and I'd booked myself in for an induction the day she was born (labour started spontaneously but I ended up having an emergency c-section) because I wanted to take control and knew the risks of continuing too far over dates (placenta can start to pack up). but I can quite understand your fear of induction.
the embryo may have just had a bit of a spurt. you could try calling the clinics you had the scans at and see if someone there (probably a consultant, not the everyday sonographer) could explain how they might account for the discrepancy, given the differnt machines and dates of your scans.

[Tinker]

Ooops sorry, read it too quickly!

[leese]

NQWWW - do the hospital want to change your 'due date' to comply with your dating scan? In our hospital we go by the womans LMP unless a dating scan alters it significantly - ie plus or minus 2 weeks. Check with the hospital, but if their protocol is the same they will not alter your EDD (expected date of delivery) if your dating scan only has a five day discrepancy.
Have'nt actually come across this before - ie two scans so close together, giving slightly different dates, as most of the women in our area are lucky to get one scan! (The nuchal is available privately, but not thru NHS, and the only other scan offered is the routine anomaly scan at 20 wks. Of course a woman may have a dating scan if unsure of her dates.) Must say tho' that often find discrepancies in scans - ie from those performed at 12 wks, and then later at 20 weeks - you should as a rule always go with the earlier scan (tho' no really applicable in your case).
Induction is an agreed process - not one that can be forced upon you, so noone will make you do anything.

[Khara]

I had a edd argument throughout my pregnancy with ds2. I knew my LMP date was correct, as we'd been ttc for about 9 months and I was using an OPK. The 12 week scan (not a nuchal one) put my edd 11 days earlier!

Throughout my pregnancy, I tried to convince them to put my due date at the LMP one, but no - the policy was that if there was more than 7 days difference, they went by the scan. (Which, incidently, means that you should be ok at only 5 days difference, NQWWW.)

As I was having a homebirth, I was absolutely adamant that there was no way they were going to induce me until I was at least 2 weeks over my dates. I made them write my objection to their edd in my notes. As it turned out, ds2 arrived 9 days late (by their reckoning), and 2 days early by mine. Ds1 was one day early - funny that!

[zebra]

NQWWW: I suspect (see other recent threads on nuchal fold) that the private test gave you a general risk, or one that only considered age in a general way. Perhaps the NHS test took into account your age? I think I understand this...One way to reckon it is that the nuchal fold only detects 80% of chromosone defect babies. So, your reduced risk is 1/5 (20%) of what it would otherwise be. If your risk based on age alone is something like 1:140, then a "good" nuchal fold would reduce the odds to 1/5 1/140... or 1:700. But if the general risk of chromosone defect babies (for all mothers over 30) were about 1:250, the risk would go to 1:1250 (=1/250 1/5). HTH.

[NQWWW]

Thanks for your comments - I have my booking appointment at the hosp on Monday so will see then if they want to change my EDD.

Zebra - no, both tests took my age into account. Both places explained this very clearly, and it is clear from the reports they have given me. The woman at the private clinic stressed that the risk for my age had been reduced by a factor of 10, which was the best possible result.

[zebra]

I don't believe your private clinic, then (sorry!). Everywhere I try to research it the nuchal fold isn't credited with detecting more than 80% of cases; I think the private clinic was exagerating their detection rate. Maybe I'm wrong, but I can't find any credible source that claims the nuchal fold is better than 80%, and some say the nuchal fold is no better than 60%.

[NQWWW]

Zebra - I think you may have answered the question. Of course! The private clinic did blood tests which they then combined with the results of the nuchal scan. So they're able to do it with a higher degree of accuracy.

I do trust them, as they are run by Prof Nicolaides who invented the whole nuchal scan thing. They also looked for the absence of a nasal bone, which is a new indicator of problems.

[bundle]

NQWWW that would make sense, especially if it was a quadruple test which is the most accurate

[SofiaAmes]

nqwww, what you got privately is the best going other than an amnio. For my second pregnancy I had the nuchal scan alone which is all my nhs hospital offered. After having the test and getting the results back which were very good (similar to yours, but I was 39), I researched it and decided I wasn't happy with the predictive ability of the test (because it relies on operator accuracy) and had an amnio as well so I could have peace of mind. I think if I had had the triple or quadruple test (what you had privately) which combines the blood test (no operator skill involved) with the scan I would have been more confident about the results and not had an amnio. Then again, the amnio does test for a variety of genetic problems that none of the other tests can predict. In my experience with both my pregnancies the midwives and consultants knew less than i did about the tests available and how good they were. Your hospital should have a genetic counselor who is specifically trained in this area and can give you real, accurate information to help you make these kinds of choices. good luck

[miriamw]

NQWWW, I can't help you on the nuchal aspect (though I agree that both risk factors are pretty good!), but I have been certain of dates with both my pregnancies (due to IVF), and by 20 weeks in both have been about 12 days out, though in my case it simply seems to mean that I have large babies (ds1 was 9lbs 3oz, I'm just 5 foot tall and pre-pg1 had size 10 hips). 5 days shouldn't make a big difference, though in both cases with me sonographer/mw/registrar all wanted to change my dates - consultant changed it back! Certainly no word of inducing me (I would have been 42w 5d by scan dates), though I had weekly scans to check growth etc at the end (but then my consultant routinely doesn't induce much before 43 weeks anyway...)

Hope the rest of the pg goes well!

[Tamz77]

I too was sure of my LMP and my cycle was always regular. At my 12 wk scan my due date was adjusted (put back) by 4 days. The midwife/sonographer were totally uconcerned - even when I protested that I had been tracking ovulation exactly - and said that they'd only be worried if my dates were out by a week or more, as any date they give you is '+ or - 7 days' anyway: thus your estimate (and mine!) is probably right. I was asked to pick a due date - 24 July 03 or 28 July 03 - and I went for the latter, specifically to lower my risk of induction! However when the time comes they take a lot of things into account: how big your baby is, how much amniotic fluid there is, the condition of the placenta, etc. On another message board I use a lady went overdue by two weeks with a first baby, home birth: if exams and scans indicate there's nothing wrong, there's no reason why you shouldn't hold on for things to start naturally.

As for your two nuchal scans: I'm no expert but I guess that the apparent difference in estimates is no real difference when you look at the numbers involved - in the high hundreds/early thousands. I know that's hardly reassuring, but it seems you're very low risk whichever you look at; it'd be different if one scan gave you a risk of 1:10 and one gave you a risk of 1:100. There may have been a teeny difference in measurement due to the difference in equipment used between the hospitals, perhaps?

[zebra]

NQWWW: I didn't think the early blood tests (it's 2 blood factors, I forget which ones) combined with nuchal fold detected more than 85% (at best) of chrom. defects... i say that partly because combining the nuchal fold, 12 week bloods and quadruple test (which you can't have until 16 weeks or so)is called the "integrated test", and even the integrated test is only supposed to be able to detect 85-92% of cases. But perhaps the tests you had narrowed the odds because of looking for the nasal bone? There is good info at Mothers 35+ , and more info at this site .

I admit that quibbling over the difference between 85% and 92% is silly, though. NQWWW's risk is very low, anyway you look at it.

[zebra]

NQWWW: I didn't think the early blood tests (it's 2 blood factors, I forget which ones) combined with nuchal fold detected more than 85% (at best) of chrom. defects... i say that partly because combining the nuchal fold, 12 week bloods and quadruple test (which you can't have until 16 weeks or so)is called the "integrated test", and even the integrated test is only supposed to be able to detect 85-92% of cases. But perhaps the tests you had narrowed the odds because of looking for the nasal bone? There is good info at Mothers 35+ , and more info at this site .

I admit that quibbling over the difference between 85% and 92% is silly, though. NQWWW's risk is very low, anyway you look at it.

[zebra]

Oh, pooh, I just did that stupid refresh trick.

[NQWWW]

Thanks for all your comments. I'm not worried about the nuchal result, I was just curious as to how there could be such a difference. I had my booking appointment yesterday and the midwife confirmed that she won't change my EDD. So I'll relax.