# Calculating due date: LMP or Ovulation??



## mara16jade

It appears there are multiple ways of estimating due dates.

1) your last monthly period
2) when you ovulated
3) date you conceived
4) ultrasound scan

Which was most accurate for you, or which one have you heard is more accurate?

If I were to go by my last LMP (October 15th) I'd be due on July 22nd. 

If I go by my ovulation date (October 25th), I'd be due on July 18th. 

If I go by my conception date (assuming October 25/26 we only dtd on the day of O and the day after), I'd be due on July 18/19th.

Oh, I should add I have 25 day cycles. :)

What do doctors normally view as the best way to guess the EDD?


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## mara16jade

Anyone? :flower:


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## Kitteh_Kat

None of them were accurate for me! LMP put me at May 14th. Scans put me at May 22nd. She was born on May 29th, and only because I was induced. I probably would have went past 42 weeks, because she did not want to come out. :haha:

In the end, the EDD is just that - an estimate. Baby decides when they're ready, unless you have a medical intervention.

Congrats on your pregnancy! Hope it go smoothly for you. :hugs:

My OB went by the scan date.


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## littlesteph

doctors will go by your last period until you've had a scan.
with this pregnancy I knew exactly when I ovulated and told the doctor that, told the doctor what I thought was my due date. he told me he couldn't go on that as ovulation test aren't accurate enough to determine when you actually ovulated. turned out I was spot on with my due date. 
so even if you know dates, they won't go by them, they'll go by last period until you've had a scan, then they'll go by the scan date.


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## mara16jade

Yeah, I'm sure they don't trust our ability to know when we O'd. 

We only did it twice during my fertile time: day of O and the day after. I'm pretty sure I got it right. LOL :winkwink:

Thanks for the responses ladies. :)


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## littlesteph

see that's what bugs me surely we know our bodies enough to know when we ovulated :haha:


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## Rachie004

See the due date they've given me has me as 40w5d going from my ovulation date and if I used my LMP then my EDD is at 41w4d. I personally can't get excited about due dates because I just think baby will come when he or she is good and ready. They had me as measuring 2 days ahead at my scan but I joked to OH that neither of us were present for conception if that is true :haha:


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## Srrme

My Doctors have always gone by my LMP. I never remember when I ovulate. :lol:


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## laceyrainbow

LMP is only accurate if you have normal 28 day cycles because it will assume you conceived two weeks after that date however somebody like me who has 70 day+ cycles, it doesn't work for.

When they went off my LMP my EDD was 28th March!! LOL! 

After my scan, it's 10th June. 

However, most doctors still just go off LMP until you have a scan because unlike someone above said, some of us barely have periods and have no signs of ovulation so it's impossible to know when it's happened! 

x


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## Sorsha

I was having long, irregular cycles when I got my BFP. My LMP would have put me at about a week and a half further along than what I was pretty sure was my O/conception date. When I explained that to my midwife, she put down my estimated due date based on the O date--and then the first ultrasound confirmed it to the day. :)


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## x__amour

Ultrasound.


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## Celesse

*1) your last monthly period*
Very inaccurate. Lots of women have irregular cycles and even more have cycles that are not 28 days. I don't have a LMP for this pregnancy (in conceived about 6 weeks after a miscarriage) and I didn't have an LMP when I was pregnant with my son (Was still nursing DD and hadn't got periods back)

*2) when you ovulated*
Ovulation is the most accurate..... however that depends on how you are measuring ovulation. Most accurate way of measuring ovulation is to have an ultrasound scan of the ovaries before and after and most of us don't have that. Other ways of tracking ovulation vary in accuracy. So how accurate "ovulation" is at dating a pregnancy depends on the method used to work out this date. 

*3) date you conceived*
You mean the day you have the sex that led to the pregnancy? Pretty inaccurate. Although there is a greater chance of getting pregnant if you have sex 1 or 2 days before ovulation you can still get pregnant from sex 5 or 6 days before ovulation. 

*4) ultrasound scan*
An ultrasound scan around 12 weeks is generally accepted as the most accurate way of dating a pregnancy. It can be out by a few days though. Both my children measured 3 days more at the 12 week scan than estimated ovulation date put them at (the scan said I had conceived 3 days before I had a positive OPK with DS and 3 days before I had ewcm with DD)


Your due date only really matters when you have to give consent for an induction. If you aren't sure and think you are less pregnant then ask for monitoring for a few days until you are sure. For things like viability in preterm birth they will try and save the baby around the time of viability regardless of the exact date. From a legal point of view they will use the scan date.


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## luz

your doctor will determine your due date based on your LMP. If you have an ultrasound and they find your baby's measurements larger or smaller than what they should be, they will adjust your due date accordingly.

My pregnancy was a total surprise, and based on my LMP i was supposed to be due November 15. However, an ultrasound at '10 weeks' showed i was actually only 5 weeks so they pushed my due date forward.


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## Celesse

luz said:


> *your doctor will determine your due date based on your LMP. If you have an ultrasound and they find your baby's measurements larger or smaller than what they should be, they will adjust your due date accordingly.*
> 
> My pregnancy was a total surprise, and based on my LMP i was supposed to be due November 15. However, an ultrasound at '10 weeks' showed i was actually only 5 weeks so they pushed my due date forward.

That makes it sound as if the doctors are in charge of your due date. They are not, the baby and your body are responsible for when labour starts and you are responsible for consenting to treatment for post dates such as an induction. 

Fair enough go with the medically interpretation of your _Estimated_ due date if you have no other date to go on, but it doesn't make it the "right" date or even the most accurate if you know your ovulation date.


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## laceyrainbow

That doesn't mean they're in charge, it just means an ultrasound is the most accurate. If you 100% know when you ovulated, then your EDD by ultrasound and YOUR EDD by ovulation will be the same. 

However, we don't all know when we ovulated. I have irregular cycles that go anywhere from 30-90+ days. I THOUGHT I knew when I ovulated which would make me 16+1 today. I just had my ultrasound and I'm 11+3. It's okay knowing but if an ultrasound CRL measurement shows something completely off, your estimations are either wrong or the baby isn't growing correctly.


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## mara16jade

I went in for an early scan due to spotting. They originally said I was 5w1d yesterday, but after the scan and measure I'm now listed at 6w today. lol So yup, they adjusted it. :)

Oh, and I was right! :winkwink:


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## Urchinia

I agree with Celesse's posts. If you know for sure when you ovulated, that is the best way to go about determining your EDD with the closest accuracy. I chart and temp, so I know when I ovulate. I loved that when I got pregnant, I could say for sure when I ovulated.

The next best means would in fact be early ultrasound. They tend to be pretty accurate!

It's kind of frustrating that so many doctors still use LMP as a way to calculate due dates, and some get so stuck on that. Like mentioned earlier, even when you know exactly when you ovulated, your due date is still an approximation! Every baby and mommy are different when it comes to how long they need to grow!


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## jenniferannex

I also say LMP then an ultrasound, when I had my dating scan at 12 weeks I was spot on to my LMP, but my Period is like clockwork, every 28 days without fail so that's probably why mine is spot on xx xx


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