While many doctors’ offices confirm a suspected pregnancy using a urine or blood test, practitioners generally follow up chemical confirmation with an ultrasound to confirm viability of the pregnancy. Ultrasounds help physicians assess the viability of a pregnancy with regard to placement of the embryo, gestational age, and visible signs of appropriate development. While abdominal ultrasounds are common in later pregnancy, transvaginal ultrasounds allow for earlier imaging of an embryo, and many practitioners prefer them for early visualization.
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The purpose of ultrasonagraphy during pregnancy is to ensure normal progression of the pregnancy. AmericanPregnancy.org explains that early ultrasounds help physicians confirm that a pregnancy is viable. For embryos of greater than six weeks gestational age, ultrasounds should show an embryo with a heartbeat and a gestational sac, located in the uterus. If the gestational sac appears to be outside the uterus, the pregnancy is ectopic, and is not viable. Embryos of greater than six weeks gestational age without a heartbeat are typically not viable.
While practitioners may choose to use ultrasound at any time during pregnancy, many will do an early ultrasound simply to confirm viability of the pregnancy before it progresses. ProChoice.org notes that transvaginal ultrasounds have the advantage of allowing visualization of an embryo much sooner than abdominal ultrasounds—typically embryos of only four to five weeks of gestational age will show up on a transvaginal ultrasound, while it takes nearly six weeks for abdominal ultrasound visualization.
A transvaginal ultrasound, unlike a traditional abdominal ultrasound, requires the insertion of a probe into the vagina. RadiologyInfo.org notes that one benefit of the procedure is that a woman need not fill her bladder with water—an uncomfortable prerequisite for an abdominal ultrasound in early pregnancy—prior to a transvaginal procedure. The ultrasound probe, once inserted, allows the ultrasonagrapher to visualize the uterus and ovaries through the cervix, which forms the barrier between vagina and uterus.
Ultrasounds provide very accurate assessments of the viability of pregnancy—a skilled ultrasonagrapher uses information from the ultrasound to determine placement of the embryo and presence of the heartbeat, both of which are unmistakable to the trained eye. Another common use of ultrasound, however, is to determine gestational age. Here, notes AmericanPregnancy.org, transvaginal ultrasound may provide a rough estimate, but can’t necessarily pinpoint the age of the embryo. The reason for this is that differences in women’s reproductive cycles and differences in embryonic growth rate affect embryo size.
While ultrasounds have not been found to cause damage to either mother or baby, they're nevertheless not done unless medically indicated. For this reason, practitioners differ with regard to their approach to ultrasounds, and some don't rely upon them heavily. Instead of ultrasounds, physicians may choose to monitor pregnancy viability and progression using blood tests for hormones and measurement of uterine size. AmericanPregnancy.org notes that it's not unusual for a woman to go through the entirety of a normal, uncomplicated pregnancy without a single ultrasound, if that's the preference of her physician.