Due date doesn't match possible conception dates

[thebuzz]

Hi

I just wondered if anyone has ever had a due date that doesn't match with possible conception dates?

I have irregular cycles so had a scan early to ascertain where I was at - and they put me at 6 weeks 6 days. Then I had my nuchal/12 week scan on tues which is when I thought I was 12 weeks 2 days but they said I'm actually 13 weeks 2 days - when I look at my cycle chart and possible conception dates it is an impossibility (ie no intercourse for 19 days before that date or 8 days after that). Which to me means the baby is longer than it should be.

Both my partner and I would not be considered tall - 5ft 5 and 5ft 11. My nuchal reading also was 3.1mm putting us at moderate risk of downs but the blood test results yesterday were good so our risk is now 1 in 1500.

I just wondered if anyone had a similar story - or if maybe I should speak to someone about the baby being bigger than 'normal'. I have a 3 year old who weighed 6lb 14oz at birth and matched her original due date all along.

I knew exactly when my ds was conceived. At the 12 week scan he was already 1 week bigger than dates. At 20 weeks he was 2 weeks bigger. I had a 36 week scan and he was so big, the sonographer had to work out the measurements by hand because the computer couldn't cope with the figures. He was born at 37 weeks and weighed in at 8lb 10 oz, which put him around the 99th centile for his gestation.

The birth was absolutely fine by the way. In fact, much, much easier than the birth of no.1 child, who weighed exactly the same as your 3 year old at birth.

I wouldn't worry about it at all. Even at 12 weeks, the baby is so small and wriggling about that I can imagine the measurements taken couldn't possibly be absolutely exact. Even a mm out could make a difference in dating. I would mention to the mw that you're measuring a week earlier than your dates suggest and leave it at that. Likely they won't be fazed in the least - it's later on that they might be concerned about an overly big baby as it could be a symptom of gestational diabetes.

Congrats on your great scan and good luck!

Generally, the earlier the scan, the more accurate it is, so I would argue that they should stick with the first scan's dates. Otherwise they will be saying you're overdue when you're not and potentially going down the road of unnecessary induction.

Thanks very much - you've put my mind at ease. I'm slightly nervous about the whole pregnancy now as we had 2 days of waiting to hear results on the downs blood test, having been told we were high risk. And I guess if they were concerned at this stage about the change in due date they would have mentioned it then.

Just got to get through the 20 week scan next.

Thanks again
x

Thanks Daisymoosteiner - I'll bear that in mind. I have my charts of cycle/intercourse dates so at least I can show them that if it came to being pushed towards induction further down the line. I'll keep the original 4th Oct due date in my head for now.

Slightly strangely I had very irregular periods too, and three dating scans to try and judge the baby's due date - particularly as she was large but not as developed as she should be at certain stages so it was causing confusion. It meant that my due date was put back about 18 days from my original estimated dates based on cycle and potential conception dates, and lo and behold she actually still managed to arrive a day after the final due date (so 19 days later than I thought). So I think I may be inclined to trust the sonographer and presume that not all babies develop the same.