Ultrasound accuracy for dating
but the dates you gave and sizes are just really off.Most dating scans are done with a trans-abdominal transducer and a fullish bladder.However, if you did not get a first trimester ultrasound for dating and an ultrasound done to look at the baby's anatomy (usually at 18-20 weeks of pregnancy) differs from your LMP date by 10 to 14 days, we would change your date to the ultrasound estimate. It looks like the dating scans were a month apart but the size actually went down a day?Also the fetus cannot bend and twist too much yet, so the length of the body is fairly constant.However, the accuracy of the ultrasound examination is always dependent on the skill of the sonographer and the quality of the equipment.
In addition to diagnostic uses, such as evaluating abnormalities in the abdomen, pelvis, and breast, ultrasounds are commonly used to guide needle and catheter placement in a variety of surgical At 5-6 weeks a gestational sac and pregnancy reaction can be seen.
If the ultrasound date is within seven days of your LMP date, we would stick with your LMP date.
Ultrasounds done later in the pregnancy are less accurate for dating, so if your due date is set in the first trimester, it shouldn't be changed.
The most accurate time is between 8 and 11 weeks gestation.
This is because the fetus is growing so quickly that there is a big difference in size from week to week.