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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. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends that pregnant women have routine obstetric ultrasounds between 18 weeks and 22 weeks gestational age in order to confirm pregnancy timing, to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, and to assess for congenital malformations and multiple gestations (i.e. twins). Additionally, the ISUOG recommends that pregnant women have obstetric ultrasounds between 11 weeks and 13 weeks 6 days gestational age In countries with resources to perform them. 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. Research shows that routine obstetric ultrasound before 24 weeks gestational age can significantly reduce the risk of failing to recognize multiple gestations and can improve pregnancy dating to reduce the risk of labor induction for post-dates pregnancy. There is no difference, however, in perinatal death or poor outcomes for babies. ==Terminology== Below are useful terms on ultrasound: * Echogenic - giving rise to reflections (echoes) of ultrasound waves * Hyperechoic – more echogenic (brighter) than normal * Hypoechoic – less echogenic (darker) than normal * Isoechoic – the same echogenicity as another tissue * Transvaginal ultrasonography - Ultrasound is performed through the vagina * Transabdominal ultrasonography - Ultrasound is performed across the abdominal wall or through the abdominal cavity 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Obstetric ultrasonography」の詳細全文を読む スポンサード リンク
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