QuestionMy last menstruation was on 9 September 2007.
After missing my menstruation in October, I took a home pregnancy test around the middle of the month and it was
positive. After calling my OB to schedule my first prenatal appointment, they opted to wait until I missed
two mentruations before they would schedule me for an appointment. My period due on 4 November never came, so I called the following Monday morning to get my first OB visit. They got me in 2 days later on 6 Nov, but I did not see the Dr., instead, I was given pregnancy advice by a nurse, and given a due date of 16 June 2008 based on the first day of my last menstruation of 9 Sept. 2008. I was then sent to the lab for all my bloodwork. She set me up for my second OB appointment to actually see the Dr. the following Tuesday on 13 November. He performed the pap, went over my risk being that I am 42 in a few weeks and he then during the first Ultrasound scan, I was happy to see the heartbeat, but then he said I was not 9 weeks, like I thought, but the baby was only measuring at 7 weeks and 4 days. That's when he changed my due date right there during the ultrasound from 16 June to 27 June. I was caught up guard and didn't think much about until I was on my way home. During our visit, the Dr. was rushed because his beeper went off and he had to go to a delivery.
I trust my Dr., because I had a good experience with him during my last delivery, but my question is why he would change the due date given my calculations. On the Ultrasound itself, it has my LMP as 9 Sept 2007 but on the bottom it clearly has the gestational age 7 weeks and 4 days. Is my Dr's Due date seem accurate? I would like to question him on the calculations, but I don't want to offend him by questioning his decision. I have 3 children and I've never experienced this confusion before.
Based on my LMP of 9 September 2007 and my baby's gestational age of 7 weeks and 4 days on 13 November,
when would my Due date be and how far along would I be as of today 16 November, 2007? I would really appreciate your help in this matter.
Hana
AnswerBased on your LMP, my calculator would show your due date to be 15 June 2008. However, calculations based on LMP alone use the average menstrual cycle of 28 days and assume an ovulation on day 14. Since most women do not adhere to this average schedule, this method of dating is highly inaccurate. More and more doctors are relying on early ultrasounds to date pregnancy. An early first-trimester ultrasound, such as you had, can accurately date a pregnancy to within a few days. Since your ultrasound shows you likely ovulated later in your cycle than the average woman, you are better off with the later due date. This will prevent doctors from rushing you into giving birth too soon, when you are not really "overdue."
Your ultrasound shows that you likely conceived on 5 October 2007. This would give you a new due date of 27 June 2008 by my calculator, which matches your doctor's calculation.
The reason the ultrasound machine still showed your LMP as 9 September is because that figure is manually entered in from your chart at the beginning of the exam. The ultrasound itself calculates the gestational age, which may not match your LMP depending on when you ovulated.
