Understanding Ultrasound, LMP and Ovulation

Jane Foley's picture


Good afternoon!

I'm trying to understand the discrepancy between gestational age as determined by ultrasound, LMP and the timing of ovulation.

On March 4th, I had an ultrasound done that showed I was 16 weeks.
On March 29th, I had an advanced ultrasound done (since I will be 35 at time of birth) that showed 19 weeks, 4 days.

As you can see, the ultrasounds agree although I did notice a range of dates when the second ultrasound was conducted (one measurement even showed as far along as 21 weeks, 1 day). According to the ultrasound dates, conception should have occurred on/around November 26th.

I am confused because I know with absolute certainty that my period was November 21st through 23rd. I was diagnosed with PCOS four years ago and have been told that I most likely have endometriosis as well.

I stayed on a birth control pill non-stop (no breaks) to control symptoms until April. My first cycle occured the first week of August. I have always run long cycles and this round didn't appear to be any different as they ranged from 35-40 days in length.

I know for certain which days my husband and I had sex (11/7, 11/25-28, and 12/1-2) so he was home on 11/26. However, with long cycles, I would expect to ovulate past the 14 day mark and not immediately following a period.

I'm wondering if I am further along than the ultrasound estimates and the light and inconsistent bleeding I experienced three days in November was implantation bleeding. I believe this may be the case because I have been experiencing movement since 13 weeks and have had definite kicks for the since 16 weeks. I was also nauseous and my breasts were tender during the week I bled (which I wrote off to hormones at the time).

Both of my previous children were small so I'm wondering if that throws off the ultrasound dates as well. My first measured 18 inches and 5 pounds, 6 ounces when born at 38 weeks. My second measured 18.5 inches and 6 pounds, 11 ounces when born at 39 weeks.




I am not sure what discrepancy you are referring to as far as dating your pregnancy. I must tell you that two ultrasounds in the second trimester, coming up with the same dates for your pregnancy are quite reliable, especially since one of the ultrasounds was a Level II type.

Perhaps you have let two days of bleeding throw a wrench into the pregnancy equation. I would disregard the bleeding you had on November 21st and 22nd. The November 7th would have been the likely time for conception previous to the bleeding. That is a full two weeks before your bleeding which could have been implantation as you suggested.

My suggestion is that you forget about all the bleeding, counting, worrying over things that don't really matter in the long run. Rely on both the ultrasound results and the fact that the intercourse dates match.

Pregnancy is a time for bonding and forming an amazing relationship with the child you and your husband have created. I believe too much science creeps its way into a woman's pregnancy. I would rather have Mommy, putting her thoughts and efforts into the mother-child connection and just enjoy!

With Regards,
Jane Foley RDMS