First week of dating
Therefore, your doctor can usually approximate you due date by taking certain measurements during the ultrasound.
If you have your sonogram between weeks seven and 13, measuring from the crown of the head to the rump will allow the doctor to determine the baby's age (and your due date) within about three days.
The pictures are usually printed out (or sometimes recorded on video) for you and the doctor.
The ultrasound takes approximately 30 minutes and isn't uncomfortable or painful at all.
If the heartbeat isn't identified at this point, your doctor will schedule another ultrasound in a week or so.
All fetuses are approximately the same size in the early weeks of pregnancy.
At 4 weeks and 3 days, a tiny gestational sac becomes visible within the decidua.
First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as the absence of fetal nasal bone or an increased fetal nuchal translucency (back of the neck) to enable detection of Down syndrome fetuses.If you have any abnormal bleeding, aren't sure of the date of your last period or had fertility treatments, your doctor will also order a ultrasound around the second month of pregnancy.At this point, the doctor will try to determine where the embryo is.Many practitioners recommend an ultrasound at six to nine weeks.
However, others will only do an ultrasound during the first trimester if miscarriage or ectopic pregnancy are suspected.
Transvaginal ultrasound, by contrast, can detect pregnancies earlier, at approximately 4 to 5 weeks gestation.