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.

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.Transvaginal scans usually provide clearer pictures during early pregnancy and in obese women.Also used is Doppler sonography which detects the heartbeat of the fetus.Doppler sonography can be used to evaluate the pulsations in the fetal heart and bloods vessels for signs of abnormalities.

3D ultrasound
Modern 3D ultrasound images provide greater detail for prenatal diagnosis than the older 2D ultrasound technology.While 3D is popular with parents desiring a prenatal photograph as a keepsake,both 2D and 3D are discouraged by the FDA for non-medical use,but there are no definitive studies linking ultrasound to any adverse medical effects.

Safety issues
Current evidence indicates that diagnostic ultrasound is safe for the unborn child,unlike radiographs,which employ ionizing radiation.Randomized controlled trials have followed children up to ages 8–9,with no significant differences in vision,hearing,school performance,dyslexia,or speech and neurologic development by exposure to ultrasound.In one randomized trial,the children with greater exposure to ultrasound had a reduction in perinatal mortality,and was attributed to the increased detection of anomalies in the ultrasound group.