Are reverse due date calculators correct?

[EmmR70]

So I've recently posted a question before of who the father could be. Thing is when using  reverse conception calculators some indicate Guy#2 as being the father because it lines up perfect with when I had my period. Guy #3 would suggest I came on my period when I was off. Could this make a difference into who the father could be?

[AnnieBrooke]

It depends on what info you are putting into the calculator.

Say a woman gets an ultrasound in her sixth week, and the measurements of the baby indicate she is due on or around August 15. She would have gotten pregnant around 266 days earlier than that.

But say a woman goes to see the doctor and he measures her stomach with a tape measure and tells her that she is about x weeks along, and she asks when a due date would be had he asks when her last period was and looks at a little cardboard wheel and says August 15. She can count back 266 days all she wants, but there is no certainty that it will reveal when she conceived.

This is even true when a woman's first ultrasound was much past about the 8th week. At the sixth or seventh week GA, measurements of the baby by ultrasound might be helpful to calculate the estimated conception date to a pretty close amount of exactness. But babies can grow at different rates than the average, and that would mean that by week 12 GA, the margin for error is +/- 7 days, and by week 40, it's +/- 3 weeks.

[AnnieBrooke]

And counting forward from a woman's last period is notoriously unreliable, since many women to not have periods that come every 28 days like clockwork. Only counting *backward* from the *next* period tells with any exactness when the woman ovulated, and of course that doesn't help a darn when she got pregnant that cycle because there is no "next" period until after the baby comes.

[EmmR70]

So as far as knowing the first day of your period is it when you see a little blood or rather spotting or the day that it actually comes heavy?

[AnnieBrooke]

My doctor always told me it was the day it actually flows. But that won't help you here too much, since your next period didn't come when you were pregnant. Unless, of course, you are looking at a chart you made of months and months of when your period came, and are trying to decide which were the 'official' first days. Are your menstrual months super regular?

[EmmR70]

Well I'm not sure about them being regular because I was on the implant, but they seemed to always come towards the end of the month and end on the 1st week if not the last week of that previous month. So idk how regular of a period being on that would be. I was on deposit before that with no bleeding at all

[EmmR70]

I meant depo*

[AnnieBrooke]

Then menstrual anything is not going to be reliable for you for purposes of trying to puzzle this out. Go with ultrasound evidence only.

[EmmR70]

Okay thanks again!!

[EmmR70]

Question; so I've gotten a 32 week ultrasound on 8/6/18 measuring  
GA (LMP) 32 WEEK
AUA  32WEEKS 2 DAYS
Weighing at 4lbs
can that mean that my earlier scans were wrong from the previous post? It now factors in guy #2 so should I consider testing him as well? Could the Dr saying Oct 1 was more right then the Dr. Saying 0ct.6?

[AnnieBrooke]

As I said before, the sixth or seventh week GA, measurements of the baby by ultrasound might be helpful to calculate the estimated conception date to a pretty close amount of exactness. But babies can grow at different rates than the average, and that would mean that by week 12 GA, the margin for error is +/- 7 days, and by week 40, it's +/- 3 weeks. You're getting closer and closer to 40 weeks, where attempting to use ultrasound measurements to determine when conception was, is practically useless because of the different rates at which babies can grow. It doesn't "factor in" anyone.