Pregnancy Symptoms: Ultrasound Techniques

No ionizing radiation is involved.

Transabdominal ultrasound: A jelly is put on the abdomen, and a hand–held sound–wave wand is moved around to look at the internal structures. The woman’s bladder must be full to help transmit the sound waves, so she may be asked to drink two to three glasses of water starting an hour before the test. This method works best later in pregnancy when the fetus is well developed. The doctor may have a scan performed during the first trimester to make sure the pregnancy is in the uterus and not outside it (ectopic pregnancy) and to assess the woman’s risk for having a miscarriage. The scan can also tell if more than one fetus is developing. During the remainder of the pregnancy, scans may be used to look for problems, assess the age and development of the fetus, check out its position, and, by 17 weeks, determine the sex. There is no risk to the woman or her developing fetus with ultrasound, and it is not uncomfortable. Ultrasounds help doctors establish the due date. Due dates can now be predicted within two to four days if the ultrasound is performed early enough.

Endovaginal or transvaginal ultrasound: A long, thin, sound–wave wand is covered with a condom and put inside the vagina. This type of ultrasound is usually performed early in pregnancy to make sure that the embryo or fetus is inside the uterus where it belongs. This type of ultrasound also gives more detail, for instance, about the structure of the woman’s cervix and the early embryonic anatomy.

Targeted Ultrasound Tests: A targeted or level II ultrasound exam provides a detailed assessment of fetal anatomy. It is recommended if there are concerns for fetal problems based on other tests or history.

Nuchal Fold Translucency Tests: A non–invasive screening for genetic defects. A certified ultrasound technologist measures the fold at the back of the neck. Measurements are then formulated to calculate the risk factor for certain birth defects. It is usually done at 10–14 weeks gestation and offered with a blood test that also screens for birth defects.