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Midwives/Period or implantation



I am wanting to get a different opinion about ultra sounds and dating.

I am currently 27 weeks. I am just annoyed at how my OBGYN always pulls out her "wheel" to calculate dates. As we know not everyone is on the same cycle.


Sept 09 2012 period
Oct 12 2012 period ( 4 days late )

I was thinking my period was to come on Oct 09, or 10. Took pregnancy test both days. Both came up negative. Than "period" came on the 12th

My issue is... I have been hearing about implantation bleeding. So now I have it in my head that Oct 12 was not a period because it was late. It was implantation bleeding.

Found out I was pregnant on Dec 14, 2012
I thought I was 9 weeks
They said 8 weeks 4 days which means in my head I ovulated a little late.

January 07, 2013 ultra sound
They said I was 12 weeks 3 days

So with my calculations I conceived somewhere near the end if October.

What are the chances that Oct 12 was implantation bleeding? Would I have measured differently at my ultrasound? And if we go by LMP would this mean we would be going on Sept 09 period?

I hope I am clear with my questions.  I was never on the pill. My periods really never come on the exact day every month. And Oct 12 even know it was late it seemed like my usual period. I had cramps and lasted 4 days.

I assume accuracy of first trimester ultrasounds to be fairly accurate.  I read so many different days they can be off by.

ANSWER: Hi, Cheryl,
If you suspect that you conceived in late October, then the October 12th bleeding could not have been implantation. Implantation occurs between one and two weeks after conception.
9 weeks is only 3 days difference from 8 weeks, 4 days.
If you're going by your LMP then you were 9 weeks, but going only by the LMP is only accurate if your periods are exactly 28 days apart, every time.
Since your periods are more than 28 days apart -  from Sept 9 to Oct 12 is 34 days - you probably ovulate closer to day 20 of your cycle (day one is your LMP, October 12th), which means you probably conceived on or around November 1st, give or take 1-3 days. Which means you are probably more likely 8wk4days.
If your baby measured 8 weeks 4 days on December 14th, the bleeding on October 12th was not implantation bleeding. If it was implantation bleeding, you would have measured 12w4d. Early ultrasounds are quite accurate, give or take a day, but not 4 weeks off. Third trimester ultrasounds can be off by as much as two weeks, but still, not off by four whole weeks.
Feel free to ask further questions for more clarification.
Best of luck,

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QUESTION: Hello again,

I was just looking at your calculations on the 12 week 4 day that would have been the measurements on Dec 14, 2012 if implantation on Oct 12, 2012 too place.

If they were to go by my Sept 09 period, would I not measure over 13 weeks.

Just unsure how you got the 12w 4d measurement.

If implantation happened on October 12, then conception happened between 1-2 weeks before, which means on December 14th you would have been somewhere between 12w1d and 13w6d, depending on when you actually ovulated and conceived in your September cycle.
The ultrasound would have been able to pick up the exact gestational age, which doesn't actually go by LMP unless a woman has regular 28 day cycles.
First trimester ultrasounds are quite accurate, and would not have a discrepancy of more than 1-3 days. So, while it is possible that the 8w4d estimate of gestational age is off by a day or two, it's not possible that it's off by enough to make the October bleeding implantation bleeding.


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