12 week dating scan accuracy
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Ultrasound scans offer an alternative method of estimating gestational age.The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation.
Performing an ultrasound at this early stage of pregnancy can more accurately confirm the timing of the pregnancy and can also assess for multiple fetuses and major congenital abnormalities at an earlier stage.Obstetric ultrasonography is the use of medical ultrasonography in pregnancy, in which sound waves are used to create real-time visual images of the developing embryo or fetus in its mother's uterus (womb).The procedure is a standard part of prenatal care in many countries, as it can provide a variety of information about the health of the mother, the timing and progress of the pregnancy, and the health and development of the embryo or fetus.Some abnormalities detected by ultrasound can be addressed by medical treatment in utero or by perinatal care, though indications of other abnormalities can lead to a decision regarding abortion.Perhaps the most common such test uses a measurement of the nuchal translucency thickness ("NT-test", or "Nuchal Scan").Gestational age is usually determined by the date of the woman's last menstrual period, and assuming ovulation occurred on day fourteen of the menstrual cycle.
Sometimes a woman may be uncertain of the date of her last menstrual period, or there may be reason to suspect ovulation occurred significantly earlier or later than the fourteenth day of her cycle.
Traditional obstetric sonograms are done by placing a transducer on the abdomen of the pregnant woman.
One variant, a transvaginal sonography, is done with a probe placed in the woman's vagina.
In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity.
Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.
Transvaginal scans usually provide clearer pictures during early pregnancy and in obese women.