Conflicting Due Dates & Fetal Size: What to Expect at 32 Weeks

Question
Hi I am having a problem believing the due dates given to me by two different sources. My family doctor gave the first one as June 8 then after an ultrasound the x ray tech said it was June 29.  I am currently 32 weeks and the baby is 3 inches below my ribcage and I have some discomfort from the baby being as long as it is. This is my 4th child all my kids were over 9lbs 6oz and over 21 inches long.  I just quit smoking and quit taking sertraline for depression about 3 months ago.  I was already getting sick in Sept and had a very short period only 3 days in Sept. Am I further along than the tech says?

Answer
Dear Rebecca,

It would help to know when the ultrasound was performed. Ultrasounds done within the first trimester are considered to be very accurate in dating pregnancies. Since having the ability to visualize pregnancies via ultrasound, we have noted certain "norms" at specific gestational ages in the early weeks of pregnancies. So, by measuring the gestational sac and CRL (crown-rump length) and also noting the appearance of certain things, such as the yolk sac or heart activity, we can date pregnancies quite accurately to within a few days.

In general, ultrasonography dating of a pregnancy is more accurate than dating using the date of the mother's last menstrual period. The biometric crown-rump measurement (CRL) of the six to 12-week fetus provides the most accurate measurement - within three days of true gestational age. From 12 to 18 weeks gestation, other anatomic structures are typically measured and biometric measurements are usually accurate to within a week of gestational age. After 26 weeks gestation, fetal variability has greatly increased and the dating provided by biometric measurement is less accurate, but the method is still used. By late in the third trimester, measurements are accurate only within a two-to three-week window. This is because babies can begin to grow at different rates due to varying factors - maternal health or lifestyle, uterine conditions, genetic factors, etc,...

So - if your ultrasound was performed during the first 12 weeks of the pregnancy, I would say you can count on the dating being pretty accurate. It sounds like your babies are genetically predisposed to being big at delivery. Also, you can have your OB doctor measure your fundus (your belly), if they aren't doing that already. If the measurement is on track with your week of pregnancy, I would say your dating is accurate.

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

Brenda