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How accurate are dating scans? Panic at possible consequences if overdue!

(14 Posts)
ingunnsch Wed 01-May-13 19:26:49

Hi ladies,

I had my first scan at 13 weeks according to my LMP, but was swiftly informed by the sonographer that I was actually nearly 15!

I was a bit shocked but didn't think much of it until a few weeks later when reading about how the NHS can bully women into having inductions when they think they are "overdue".

So now I'm really worried and would like to know how accurate these scans really are, and also if there is a way to change my EDD back to the original, LMP-based one.

Thanks for reading!

snickersnacker Wed 01-May-13 20:10:22

How sure are you of your LMP dates? Many midwives are very woman-centred and happy to work from your dates if you're absolutely sure of them.

ingunnsch Wed 01-May-13 20:14:15

I am absolutely sure of my dates, and absolutely sure I had a 'proper' period and not just spotting.

Do you think I can raise this with my midwife and possibly have my EDD changed back?

quertas Wed 01-May-13 20:43:27

They won't change your EDD on your notes but if you are sure of your dates then stand your ground. Both my babies have measured a week ahead at 12 week scan and only a few days ahead at 20 week so I just figure they grow fast and then even out the pace. My midwife this time questioned my dates and I said "well look my partner and I have full time jobs each, we have a toddler, two dogs and a horse. If there's an occasion for getting pregnant it does tend to stick in the mind". At which point she laughed and hasn't mentioned it since smile

rootypig Wed 01-May-13 21:00:44

Up to 12 weeks, dating scans are said to be more accurate than LMP EDD. After 12 weeks, genetic factors play a role in the size of the foetus. That's how it's been explained to me.

Which based on my experience is utter bollocks grin

I had DC1 6 months ago, and my EDD was revised forward a week based on my dating scan (ie I thought I was 12 weeks but was told I was 13). I was VERY dubious, as I was almost certain of the day I ovulated, and this put my conception before that hmm. And I had the same concern that you did, and discussed it with my midwife, but she was very clear that they wouldn't let me go more than 10 days over the (dating scan) EDD, ever - because the risk of being more than two weeks over EDD is much greater than induction. In my borough (Hackney in London) they induce at 41+3 to ensure delivery by 42. They were absolutely implacable.

In fact I went into labour a few days before that, at 41 weeks (or 40 based on my LMP, just saying grin) The day they booked my induction I thought, right, not having this, and spent the day slogging round department stores. Did the trick!

rootypig Wed 01-May-13 21:04:20

how far along are you at the moment OP? is it your first baby?

KippersAndMackerel Wed 01-May-13 21:12:45

You might have ovulated around the time of your period rather than 14 days after as is more common? In which case you would have conceived 2 weeks before you calculated using your LMP date, making the scan correct. I think there is a 3 day standard deviation either side of predicted conception date, but its very unlikely to be any further out early in pregnancy.

MyNameIsAnAnagram Wed 01-May-13 22:06:51

You cannot be forced into induction, it is perfectly ok to decline and have expectant management instead.

Rockchick1984 Thu 02-May-13 09:31:13

Was just about to say the same as Anagram even if you agree on your dates they can't force you to be induced, it's your body!!

If you refuse induction they will invite you in daily for monitoring to check the placenta is still functioning correctly, you can then request induction if and when you feel it's the right time for it.

BraveLilBear Thu 02-May-13 11:23:31

Hi ingunnsch I know exactly how you're feeling. I was dated 7 days ahead on my 12 week scan and had the exact same concerns. I had an early miscarriage immediately before my BFP, which was taken as my LMP. But I usually have a 32 day cycle and I get ovulation pains (which always tally to 14 days before AF), so know I ovulated 5 days later than normal.

But the scan put me a week ahead of that. I raised my concerns with my midwife and, after explaining why I was so sure the date was wrong, she said two things. One, no-one can force you into having an induction and if they do, get them to speak to me, and two, you might actually want to have it by then anyway.

Since then, my 20 week scan measured bang on the same dates and at 28 weeks, my bump is measuring exactly 28cm.

I am still convinced that 'my' dates are accurate, and am also petrified by the prospect of being induced, but I'm seeing it from a point of view that if it is that big, then would I really want to carry it a lot longer and end up with a difficult birth?

If the dates don't match by 20 weeks, they can always change the EDD at that point as far as I know, too.

ingunnsch Thu 02-May-13 23:01:01

Thank you all for your replies!!

I have my 20 week scan next week, so will check then to see if the dates coincide with the first scan. And even if they do, I will have a word with my midwife so that AT LEAST my dissatisfaction at the change of EDD can be written on my notes.

Good to know that, ultimately, I am the one who decides if I want an induction or not (most certainly not!) or a C-section (again, most certainly not unless strictly necessary - already had a horrendous experience of those with my first birth!)

Fuckwittery Thu 02-May-13 23:04:10

I was told by a sonographer that 12 week dating scans if done at 12 weeks have a +\- 7 day margin of error. Your 20 week scan even less reliable +\- 3 weeks after 20 weeks.
This is why I declined induction and had daily monitoring and went by hosp dates 18 days overdue!

NaturalBaby Thu 02-May-13 23:07:45

My scan dates put me ahead by up to a week with all my pregnancies and I had a flap about induction with my first - my lovely mw explained that I could refuse induction and would be offered scans to check placenta function as I neared 42 weeks. In the end 2 of them arrived within a few hours of their due dates, and ds3 was a couple of days overdue (early by my dates).

Blending Thu 02-May-13 23:39:25

I was certain of my dates as I had IVF! Still didn't stop them changing them, both times, both brought forward.

I went into labour the day after I thought I was due with dd, but due to circumstances she wasn't born until a few days later by crash section.

This time I'm having twins, and having a elcs but they have compromised slightly on dates, as I really don't want them out too early if possible, so we've decided on 37 +3.

Good luck.

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