Last period, ovulation and EDD

[mara16jade]

OK, so I've been browsing BNB and I got a little confused when people started talking about their EDD.

https://www.pregnology.com/due-date.php

If you put your information in there, you'll get two different dates if you go by the day of your last period or ovulation day.

I'm not TTC so I put in false information based on a 26 day cycle (since my cycles are 25-26 days long).

Does anyone know why there'd be a difference in EDD if you put your last known period date or the day you O'd?

The data I put in, in case someone wants to replicate what I saw was:

Last period date: August 1, 2013
Cycle length: 26 days

Ovulation date: August 16, 2013

 

[mara16jade]

Bump?

 

[Amygdala]

The difference will result from the programme assuming you have a 14 day luteal phase (time between ovulation and period). You put in a 26 day cycle, so the programme would assume you ovulated on cycle day 12, which would have been the 12th. For the ovulation you put in ovulation on the 16th, so the due date you get would be 4 days later. Make sense?

 

[Guppy051708]

^WSS.

It is based on an average 14 day LP but not all woman have a 14 day LP, reguardless of the length of their cycle. Some women have extremly short LP (<9 days) while other women have LP that run 16+ days, even if all of those woman have 26 day cycles.

It is alway more accurate to go by your specific ovulation date than any other calcultion. Most women dont have any clue when they ov. so basing EDD off calculators, # of days in cycle, and LMP is the next best thing (outside of an early dating u/s).

I have a 32 day cycle, and w DS1 they made my EDD August 23rd, the problem is that they assumed a 14 day LP w ov. on CD 18. the issue w this is that i only have 10 day LP, which means my ov. date wasnt until CD22. The reason why that is a problem is bc when you get to the end you are a suddenly "overdue" you dont have that extra time that you should. So really my EDD should have been 4 days later. I went overdue according to their dates, but i was charting and really i would not have been pressured so early had they gone by my Ov. date and not by their calulators. And in most parts of the USA induction talk starts like the very day you are overdue, so it got stressful for me bc i knew i wanted a natural birth and instead of spending those days enjoying being pregnant, i was in a high pressure situation all bc of EDD being based on a stupid calculator and not actually on my own body's ov. date.

so going by ovulation not only "buys you time" at the end, but it also means your baby is getting to cook longer or the proper amount of time baby needs to (if induction looms). It also means if you get induced and the dates are off, you could be inducing too early.

 

[mara16jade]

So then you're supposed to count 40 weeks from your ovulation date?

Does that still mean that at conception, you're still considered ~2 weeks pregnant because that's when you got your last period, or are you starting the clock at ovulation?

Thanks ladies!!

 

[Guppy051708]

Im not exactly sure of the science of that, i just go to a calculator that bases EDD off of ovulation. They have all been accurate for me. Even my MWs adjuster based on my ov. date reflected the same as did an early u/s.

Try this and use the "calculate from ovulation" option.
https://www.tubal-reversal.net/pregnancy-due-date.php

So, hypothetically lets say your ovulation date was August 16th, 2013 You would be due May 9th, 2014 if it were based on ovulation. If you did it based on your given hypothetical LMP you would be due May 8th, 2014.

Do you have any idea what your LP length is? or what CD you typically Ov. on? That would be more helpful.

 

[mara16jade]

My average LP is 12 days. It ranges from 12-14 actually...but more often than not its 12.

So then going by CD, it would be about CD13 - but ranges CD13-15.

I've never been exact when it comes to cycles, but it usually only differs about 2 days.

 

[Amygdala]

So then you're supposed to count 40 weeks from your ovulation date?

Does that still mean that at conception, you're still considered ~2 weeks pregnant because that's when you got your last period, or are you starting the clock at ovulation?

Thanks ladies!!

You count 38 weeks from ovulation, because on the day of ovulation, you are considered 2 weeks pregnant.