Pregnancy dating ultrasound procedure
It does not use or other types of radiation that may harm your fetus.It can be done as early as the 5th week of pregnancy. It can find things such as the size and position of the fetus.
The measurements are from one end of the fetus to the other, known as the crown-rump length, or CRL. This scan is usually done if you are unsure about the dates of your last menstrual period (LMP) or have irregular periods.The first-trimester screening test uses ultrasound to measure the thickness of the skin at the back of the baby's neck.This screening also includes blood tests that measure the levels of two substances that may be related to birth defects. If so, you will be asked to drink water or other liquids just before the test.Very high frequency sound waves of between 3.5 to 7.0 megahertz (i.e.3.5 to 7 million cycles per second) are generally used for this purpose.
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Sometimes the sex of your fetus can be seen by about the 18th week of pregnancy.