QuestionHello Brenda. I am pregnant with my 7th child. My last monthly period was 10/16/07, which would give me an approximate due date of 07/22/08. However, over the course of the last few months, my doctors have given me due dates ranging from 07/08/08 to 07/25/08... This is a very large discrepancy to me, and I am absolutely certain of my LMP. I've had 4 ultrasounds. The first was on Nov. 25th and the embryonic measurement/gestational age was 6w 2d, the second ultrasound was on Dec. 6, GA was 7w 1d, the third ultrasound was on Jan. 8th, GA was 13w 1d, and the latest ultrasound was on Feb. 27th, GA was 20w 1d... The first ultrasound was within one day of my estimate of GA based on LMP, the second put me a few days behind, and the subsequent 2 have put me at over one week ahead of my original due date... I am wondering why there is such a large difference in GA based on these ultrasounds... According to some of the due dates I've been given, I would have conceived one week after the first day of my LMP. Is it possible that my original date is correct, and the fetus is simply growing large for his age? The father was 24 inches long and 10 pounds at birth (this is our first child together) - When would conception most likely have taken place? (cycles lasted approx. 27 days, with bleeding lasting from 5-7 days - in this case my period was only 5 days) Also, I would like your opinion on what would cause a healthy fetus to be bigger than LMP weeks would indicate. Thank You!
AnswerDear Laurie,
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, genetics, etc,...
As a general rule, the early ultrasounds are considered to be the MOST accurate in dating a pregnancy and there really is no reason to change a due date based on subsequent ultrasound measurements due to the varying growth patterns that can occur. If I were you, I would feel very confident in the LMP calculation and the initial two ultrasound dating results.
I hope this has helped you and answered your question. I wish you well - especially with the 7th! Whew!!
Brenda
