Birth Control Pills & Pregnancy: Understanding Post-Pill Bleeding & Conception

Question
Dear Norman,
I took the microgynon pills for One complete month(October 2010) without having intercourse and received my regular menstrual cycle in October and then for a llittle over two weeks in November 2010 and stopped taking the pill because my husband was stil away. When I stopped taking the pill in November, I had a withdrawal bleeding on the 28 of November.(I had two bleeding cylcle in Novemeber).My husband returned in mid December 2010 and we had intercourse. I found i was pregnant by the first week of January 2011.
I am confused. Is my due date September 4 when calculating from my date of withdrawal bleeding or should it be calculated from the date of muy last regular menses in mid November?

Answer
Hi Rhoda,
When a woman goes off the pill, her next ovulation is often delayed, so it's hard to calculate a due date.  It sounds like you probably got pregnant mid December, so I would calculate your probable due date from that.  For example, if you had sex with your husband Dec. 15 and got pregnant that day, your due date would be Sept. 8 (which assumes a last period 14 days before conception, which is what we often do).  The other way to know is if you had an ultrasound done the in the first 3 months.  That will be accurate to within 7 days for knowing your due date.