QuestionMy LMP was 7/21/07, I did not go to the dr. until 10/11/07 at which time the dr used the doppler and we heard it's heartbeat. I felt quickening at 17 weeks, but when I went in for my ultrasound they are dating me due 5/26/07 instead of 4/29/07. If the ultrasound is correct, how did we hear a heartbeat at 7 weeks, and how did I feel quickening at 13 weeks? I go to the dr. in 2 weeks, I'm kind of worried about what is going on.
AnswerThe first possibility that occurs to me is that you may have misread the ultrasound. Using an LMP of 7/21/07 in my calculator gives a due date of 4/26/08, only one digit off of 5/26/08.
The second possibility is that you are growing a smaller-than-average baby. This is why second-trimester ultrasounds are so inaccurate at dating a pregnancy. Once you pass about 10 weeks gestation, fetuses start to vary in size and shape, just like the babies and adults they will become. A second-trimester ultrasound can be weeks off in dating a pregnancy. If you ovulated a little later than day 14 of your cycle (normal; very few women actually ovulated on day 14), and if your baby is a little smaller than average (also normal; average is just a number), then this would account for the discrepancy in the due dates.
Don't worry. The only reason to be concerned if a baby is measuring a little small for dates is if the proportions between the head and abdomen are wrong, something known as asymmetrical IUGR. If this had been seen, your doctor would have said something to you. Ultrasound dating in the second trimester should never be relied upon.
