Your pregnancy is dated from the first day of your last menstrual cycle.
For many women, this means you’re 4 weeks at about the time of your missed period, and 6 weeks pregnant about two weeks after your missed period.
This type of dating is based on averages, as many women ovulate about 14 days after the start of their last period, and expect a new period 14 days after ovulation.
However, the exact day of ovulation can vary from woman to woman and cycle to cycle.
Repetitive arrays of ultrasound beams scan the fetus in thin slices and are reflected back onto the same transducer.
Standard Ultrasound – Traditional ultrasound exam which uses a transducer over the abdomen to generate 2-D images of the developing fetus .
3.5 to 7 million cycles per second) are generally used for this purpose.
They are emitted from a transducer which is placed in contact with the maternal abdomen, and is moved to "look at" (likened to a light shined from a torch) any particular content of the uterus.
The purpose of the dating scan is to: Some abnormalities may also be detected at this scan, such as neural tube defects (spina bifida is a type of neural tube defect).
This depends on whether you have agreed to have the screening and when the scan takes place.