Ovulation Timing After Coming Off Birth Control: What to Expect

Question
Hi I have a confusing question but I'll try to make it sensible! I'm 33 weeks pregnant and curious about the time I concieved! My periods were pretty normal around the time I got pregnant however in mid july I came off the pill which caused me to have some bleeding the next day and my period came a week later than normal it was heavy and 4-5 days! My question is when you come off the pill like I did and it irregulates your period does that change your ovulation day for the next month? I'm told that I conceievd early sept around the 3rd and that I was around 7 weeks pregnant for my first ultrasound done on oct 9. However my concern is that my period for august was thrown off too and was the last week of aug. Seeming that I with my lmp dates I concieved early but when I think back to before I got thrown off I would have been ovulating the around the time the ultrasound says?! Can you help me?

Answer
Dear Lisa,

As a general rule, women will ovulate approximately 14 days before the onset of the next period. But because your menstrual history is slightly unreliable, (and actually even if it wasn't) your most accurate and reliable piece of information is the 7 week ultrasound. Early ultrasounds are quite accurate in dating pregnancies. As time has passed and we have been able to visualize more and more pregnancies through the years, we have come to know that pregnancies develop at pretty constant rates for the first 12 weeks. We know that at a certain week, the measurement of the gestational sac and/or embryo should be at a certain point to within a few cms. We also know that at a certain point we should be able to visualize certain things. For instance, at 5 weeks we should be able to see a yolk sac and a 6-7 weeks we can typically see heart activity. Now, after the 1st trimester, babies can begin to grow at different rates due to varying factors - maternal health or lifestyle, uterine conditions, etc,...

So, if you were determined to be 7 weeks on 10/9, that calculates back to an approximate LMP date of 8/21 and an estimated conception date of 9/4. This would make you 33 weeks, 6 days today and your estimated due date would be 5/27.

I hope this has helped you and answered your question. I wish you well.

Brenda