Every pregnant woman wants to know her due date , and a due date that is calculated from her last menstrual period with a due date calculator often doesn't match the due date that is estimated by her first ultrasound also known as a sonogram. During an ultrasound, a technician will spread a warm gel over the lower part of your abdomen and then press a tool called a transducer against your belly to examine your fetus using sound waves. An image of your fetus will appear on an accompanying computer screen and while looking at this image, the technician will take some standard measurements from different angles and listen for a heartbeat. Don't worry: This type of exam is painless and risk-free, and seeing your baby for the first time will likely be an enjoyable experience. Naturally, one of the most common questions asked about ultrasound accuracy is: Just how accurate are the due dates that are predicted by an ultrasound? Evidence suggests that, in the first 20 weeks of pregnancy , the first ultrasound may be the most accurate tool for predicting when your baby will be born.
Ultrasound Examination | Establishing the Gestational Age of the Pregnancy | Ultrasound Care
Early pregnancy roughly spans the first ten weeks of the first trimester. Occasionally, early pregnancy is unintentionally imaged by CT or sometimes MRI is done for some concurrent pathology, and its important to know the imaging findings 3. The earlier in pregnancy a scan is performed, the more accurate the age assignment from crown rump length. The initial age assignment should not be revised on subsequent scans 5.
Researchers have mapped out the expected measurements for specific points in early pregnancy , so an early ultrasound scan can give a doctor some important information. For this purpose, an ultrasound is considered a highly accurate means of dating a pregnancy. In a normal pregnancy, the ultrasound results can provide an estimate of the gestational age to within five to seven days of accuracy. In the first trimester, doctors usually use a transvaginal rather than abdominal ultrasound to gather information about the pregnancy.
With transvaginal ultrasound, checking for embryonic development known to occur within a certain time frame more accurately dates a pregnancy. Transvaginal ultrasound can see embryonic development about a week before transabdominal ultrasound, the American Pregnancy Association APA states. A transducer, a wand-shaped probe, is inserted into the vagina and pressed against the vaginal walls directly next to the uterus. It records high-frequency sound waves that create an image see Reference 4.