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Discussion Starter · #1 ·
Sorry if this is a silly question, but I'm finding conflicting info on the web!

To calculate my LMP gestation, do I add 2 weeks from the date of conception? Or do I add a week? I've seen both.
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The calculation of due date from LMP is based on the myth that ovulation always occurs at day 14 of your cycle. Calculation of pregnancy being 40 weeks long is based on 40 weeks from the LMP. So, actually, baby is only 38 weeks in utero at that point, since prior to ovulation, but after LMP, baby doesn't exist, but it's still counted in pregnancy. Does that clear it up for you, or did I make it worse?

Basically, if you're trying to figure out how many weeks along you are, add two weeks from the date of ovulation and then you'll be talking the same language with your care providers.

HTH.
 

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Discussion Starter · #3 ·
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Originally Posted by Mindi22 View Post
The calculation of due date from LMP is based on the myth that ovulation always occurs at day 14 of your cycle. Calculation of pregnancy being 40 weeks long is based on 40 weeks from the LMP. So, actually, baby is only 38 weeks in utero at that point, since prior to ovulation, but after LMP, baby doesn't exist, but it's still counted in pregnancy. Does that clear it up for you, or did I make it worse?
Hehe...yeah, that's the part I understand but it doesn't make logical sense to me since you're counting time the baby wasn't even there!


Quote:

Originally Posted by Mindi22 View Post
Basically, if you're trying to figure out how many weeks along you are, add two weeks from the date of ovulation and then you'll be talking the same language with your care providers.
Okay, thanks! That's the part I wasn't sure about...whether you add two weeks or one week. Thanks again!
 

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But personally, I'd consider only adding one week and telling them that you're not as far along as you know you are
Midwives and hospitals often have some very funny opinions on going close to or past 42 weeks, and it can sometimes be a help if you say "well, by LMP I'm not even due until next Thursday..." Just a thought.
 

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Umm, instead of calculating your LMP, can't you actually just use the date that you last saw AF? I think that some of the reasoning behind using LMP is that most women know or can figure out when their last period was, whereas unless you were actually TTC/ obsessive/ extra-knowledgable about your own system, you wouldn't know when you ovulated or conceived. It gives a concrete start-date, so to speak.

Are your cycles very irregular, or is there some other reason why you don't or can't use the actual LMP?
 

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Discussion Starter · #6 ·
I calculated my due date based on date of conception. The cycle we conceived was coming off an annovulatory cycle, so it was actually irregular because I ovulated much earlier than normal. I just needed to know how to scale the more precise date to the less precise date that most of the practitioners use, which assumes that all women ovulate on the same day!
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becasue this cycle for me was really long from the injectables, my doctor counted mine as 2 weeks before my IUI.
 

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Quote:

Originally Posted by snozzberry View Post
I calculated my due date based on date of conception. The cycle we conceived was coming off an annovulatory cycle, so it was actually irregular because I ovulated much earlier than normal. I just needed to know how to scale the more precise date to the less precise date that most of the practitioners use, which assumes that all women ovulate on the same day!
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I see! In that case, I would just add two weeks to your O day. I also ovulate early in my cycle, but just by a few days, usually day 11. I didn't figure that it made much of a difference, since due dates are so approximate anyways. "Plus or minus a few weeks", is what they should say!
 

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Quote:

Originally Posted by WeasleyMum View Post
Umm, instead of calculating your LMP, can't you actually just use the date that you last saw AF? I think that some of the reasoning behind using LMP is that most women know or can figure out when their last period was, whereas unless you were actually TTC/ obsessive/ extra-knowledgable about your own system, you wouldn't know when you ovulated or conceived. It gives a concrete start-date, so to speak.
For the overwhelming majority of women, it won't work right.
Take me, for example-- while typically my cycles are very regular (though I rarely if ever ovulate on day 14) last month my cycle was obscenely long. My LMP began on 25 April. I didn't conceive until 26 May.
: Before I had kids, I typically had 21-22 day cycles and ovulated on or around CD11. Again, my LMP would never indicate this.

As to calculating your own due date-- there are ways to do it that are more accurate for yourself. With my son, for example, I should have expected to go a bit early because my cycles were generally shorter. He was born at 37w3d, and weight 7 lbs 8 oz. That's big for a kid three weeks early, but it's *perfectly average* for a baby born at term. He was a little bit undercooked, but not much; I think he was meant to be in probably another day or two but no longer.
 

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Does that really happen often? I mean my local hospital, they won't even consider induction or anything before 42 weeks. My sister carried my niece to damn near 43.
The last week she went in for regular non-stress tests, but she was huge and desperate to have it over with (42+ weeks + mid-July + hot year = miserable person).
 

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I'm having trouble with this, too. Based on conception, I'm due Feb 26. Based on cycle length and LMP, it's the 27th. I should probably go with the latter since it's a day later, but I so prefer even dates. Plus, only something like 5% of women birth on their actual due dates, so if it's a 'fake' number anyway, I may as well pick one I like. (Although my Mom did go into labor on her due date BOTH times she had kids!!). I hope to find a midwife who doesn't have "postdates" in her vocabulary so I don't have to worry about fudging my EDD. But I'm not above doing it. I'll just pick an even day in early March
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