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How is due date calculated?

shannonaliseshannonalise
in 1st Trimester

Hi ladies,

I called my OB/GYN today to tell her I was pregnant. She asked me when my last menstrual cycle started and I told her July 22. She said, "You're about 4 weeks pregnant." 

How can that be? I am only 10 DPO today... 

I was thinking that at most I would be about a week along... right? Can someone shed some light on this? 

Thank you! 

PS - I posted earlier about being afraid to trust my 10 DPO pee stick BFPs and I took a digital and still got a BFP so I'm feeling much better about the whole thing! Thanks for your advice. :)

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Re: How is due date calculated?

  • cbm3228cbm3228
    Unless you have a dating sonogram it is calculated from the first day of your last period.  That's not super scientific unless you actually O'ed at 14day, but generally it's in the ballpark (or if you know the day you O'ed or concieved)   Therefore, they day you get preg you are actually ~14days or so along already.
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  • shannonaliseshannonalise

    imagecbm3228:
    Unless you have a dating sonogram it is calculated from the first day of your last period.  That's not super scientific unless you actually O'ed at 14day, but generally it's in the ballpark (or if you know the day you O'ed or concieved)   Therefore, they day you get preg you are actually ~14days or so along already.

    Interesting! I actually O'd pretty late this cycle. Thanks for the info!  

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  • CakerQueenCakerQueen

    Yep, that's what my doctor told me too.

    I'm only 20 DPO, and I'm 4 weeks 6 days pregnant?? I didn't O until July 29.

    What my doctor said is that they just cannot trust my O date, therefore they go by the first day of my last period.

    It still doesn't make much sense to me!

    My sweet girl born April 17, 2011. http://i52.tinypic.com/dzw4md.jpg
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  • shannonaliseshannonalise
    imageCakerQueen:

    Yep, that's what my doctor told me too.

    I'm only 20 DPO, and I'm 4 weeks 6 days pregnant?? I didn't O until July 29.

    What my doctor said is that they just cannot trust my O date, therefore they go by the first day of my last period.

    It still doesn't make much sense to me!

    You would think it would make more sense to trust your calculations of when O occurred than to assume you O'd on CD14 by calculating it from the first day of your last menstrual cycle. They can't trust your calculations (probably involving BBT, CM, etc.), but they choose to cling to the old belief that "the average woman ovulates on CD14?" 

    Hm.... Indifferent

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  • m0132m0132
    I read they just take the day of you LMP and then add 9 months plus 7 days. Thats what they did with DD and calculated everything from my LMP, same thing this time around..LMP was July 15th and they said I was 4 weeks along. I read that basically they count all that other stuff before ovulation as "being pregnant" even though you aren't technically pregnant, so you pretty much have a head start. I don't know how that all makes sense but I guess its just easier for healthcare providers since a lot of people get pregnant without charting so how can they know when you ovulated, you know?
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  • CakerQueenCakerQueen

    imagem0132:
    I read they just take the day of you LMP and then add 9 months plus 7 days. Thats what they did with DD and calculated everything from my LMP, same thing this time around..LMP was July 15th and they said I was 4 weeks along. I read that basically they count all that other stuff before ovulation as "being pregnant" even though you aren't technically pregnant, so you pretty much have a head start. I don't know how that all makes sense but I guess its just easier for healthcare providers since a lot of people get pregnant without charting so how can they know when you ovulated, you know?

    Yeah, you're right I'm sure it is much easier to do it this way.

    Hey, we have the same dates. My LMP was July 15 as well!

    My sweet girl born April 17, 2011. http://i52.tinypic.com/dzw4md.jpg
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  • JennieMatt10JennieMatt10 member

    going by your last period is the only way that 40 weeks can fit into 9 months.....

    Its also confusing when your like 6 weeks 2 days but they call it 7 weeks (or week 7). Whenever i'm reading about how far I am and whats happening I'm never sure if I have the right week

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