What Is a Limited Obstetrical Ultrasound?

Limited obstetrical ultrasound is an important tool in the care of pregnant women and their babies.

An obstetric ultrasound or sonography is a procedure that uses high-frequency sound waves to produce pictures of a baby inside the mother’s womb. It also shows pictures of the mother's uterus and ovaries. It is an excellent tool to monitor the well-being of the mother and baby because it is a safe and painless procedure.

An obstetric ultrasound is an important part of ante-natal (before the delivery of the baby) care. It can provide a lot of information about the pregnancy such as

• Presence of a living embryo or fetus
• Age of pregnancy
• Expected date of delivery
• Presence of any abnormalities of the fetus
• Presence of an ectopic pregnancy (the embryo or fetus is present outside the womb)
• Position of the fetus inside the womb
• Position of the placenta and diagnosis of any placental abnormalities
• Number of embryos or fetuses (diagnosis of multiple pregnancies)
• Amount of the amniotic fluid around the developing fetus
• Presence of any opening or shortening of the cervix
• Adequacy of fetal growth
• Fetal well-being

A limited ultrasound, as the name suggests, is performed to know about a specific aspect of the pregnancy such as the location of the embryo/fetus (inside the uterus or ectopic), whether the pregnancy is viable and the gestational age. A limited ultrasound does not provide detailed information about the fetal well-being or gender. It just answers the most basic and crucial questions. In early pregnancy, a limited ultrasound is important to rule out or diagnose an ectopic pregnancy (a pregnancy where the embryo is present outside the uterus), which is a dangerous condition. It may be done during labor to know about the position of the baby inside the uterus. A limited obstetrical ultrasound quickly helps determine the management of conditions such as vaginal bleeding during pregnancy. In such a situation, the ultrasound can tell whether the baby is alive or there are certain placenta abnormalities such as a low-lying placenta (when the placenta covers the cervix).

For example, if a woman is in labor, a limited ultrasound exam may be done to check the fetus’s position in the uterus. If a woman has vaginal bleeding, an ultrasound may be used to see if the fetal heart is still beating or if the placenta is too low.

The number of ultrasound examinations required during pregnancy may vary depending on the presence of any complications or need for frequent evaluations. The obstetrician is the best person to tell how many ultrasonography exams a woman needs. It is recommended that at least one standard ultrasound examination must be done during the pregnancy. This is generally done at 18 to 22 weeks of pregnancy, although some women may have the examination done in the first 12 weeks (first trimester) of pregnancy. The ultrasound examination in the first trimester does not provide details about the limbs and organs of the fetus. It can, however, help provide information about several important aspects such as the estimated gestational age, whether the pregnancy is ectopic and the number of fetuses as well as screen for certain genetic conditions.