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  1. #1
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    Default Calculating due date question?

    I am a little confused about calculating due dates for pregnancy. As far as I know, doctors always count 40 weeks from the first day of your last period, but the actual pregnancy lasts 38 weeks from conception/ovulation. I have longer cycles and usually ovulate around day 24, not the average day 14. Does this mean my due date will be out by about 10 days? How does this work? I know doctors do it from first day of last period for consistency but unsure how it works when you know you definately ovulated around day 24. Anyone else had a similar situation?

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    I would add 10 days to the date of your LMP when telling the dr.

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    With DD I got pregnant straight off the pill but did not ovulate for about 5 weeks after my last 'period', so my dating was all done by ultrasound. Yet when booking at the hospital they still wanted my LMP date, despite my protests of it having absolutely no relevance to bub's gestational age.

    This time, as I know I ovulated on CD16, I have just told my doctor from the start that my LMP was the 5th (it was actually the 3rd). As you have 10 days I would do this also, just tell them the 'wrong' (LMP+10) date - then you'll never have panic over bubs growth being behind based on LMP. Since they also like to get babies out before 42 weeks, 10 days could make a big difference eg. some stickler, who's looking at your lmp, might be panicking because they think you are 41+3 when you are only 40wks arguing that you don't 'know' when you ovulated.

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    Bubbles10  (03-03-2013),ExcuseMyFrench  (03-03-2013)

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    I agree with both pps. Tell your GP a white lie as they will assume they know better than you do.

    10 days would make such a big difference in the end.

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    GPs often ask how long your usual cycle is though too. Sounds like if you got a dating scan, then you would have a better idea regardless.

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    If you know exactly when you O, isn't better to go with that date then with a dating scan though?
    I assume dating scan can be a little off?

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    I'd get a dating scan.

    As a pp said there are websites which factor in your cycle length.

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    Thanks everyone for the replies, I might say a later date in between & look into a dating scan! These long cycles make it so confusing!

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    The Bubhub calculator factors in your cycle length


 

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