Pregnancy After Mirena IUD Removal: Conception Timeline & Possible Timing

Question
I am pregnant and very frustrated with trying to figure out my due date. The first day of my last period was 06/20/08, and I had my IUD removed on 07/07/08. I had some spotting after it was removed. The dates I could have conceived would have been from 6/24-7/15 and my first positive pregnancy test was on 07/21/08??? Is it possible to conceive prior to the IUD being removed?  I'm so confused! My husband and I are excited we conceived so quickly, but haven't a clue when we are expecting! Will we have to wait for an ultrasound to find out?

Answer
Hi Cassie,

First of all, congratulations on your pregnancy!

Women with IUDs still ovulate, the IUD mainly works by preventing sperm from joining with an egg. Some women may not ovulate when using the Mirena IUD because it contains some hormones, but that is not true for all women. While it is possible to conceive with the IUD, as long as it is in place correctly that chance is less than 1%.

It is much more possible to become pregnant so soon after removal if your IUD is removed around the same time you would ovulate.
I think this is what happened in your case. Since sperm can live inside your body for up to 5 days, having sex right before removal or soon after can result in pregnancy if you ovulated. Women who don't want to become pregnant should actually avoid having their IUD removed for this reason.

If last period was 6/20/08, the day you most likely would have ovulated was 7/4/08 if you had a 28 cycle. My thoughts are that your cycles are a bit longer (or at least this one was) and you ovulate sometime during those first few days after the IUD was removed.

Lets say the 8th, which would have given you a cycle of 33 days.

Adding 6/20/08 and 33 days into this calculator gives a due date of March 31, 2009:

http://www.babycenter.com/pregnancy-due-date-calculator

If you didn't ovulate until the 15th, you would have had a 40 day cycle and your due date would be April 8. However since you had a positive test on the 21st it is more likely that you ovulated earlier than this. If you have a fairly regular cycle, you can enter that number into the calculator.

The ultrasound will be able to give a more accurate date than I did, but I think this is probably very close and your due date is around  April 1.

I hope this has helped, if you have further questions let me know.

-Mia