What types of ultrasound are used during pregnancy?

There are two approaches used during pregnancy, namely transabdominal (through the abdomen) and transvaginal (via the vagina).

The transabdominal ultrasound is the more commonly used approach, especially after 12 weeks of pregnancy (when the uterus has protruded out of the woman's bony pelvis). An ultrasound probe placed on the woman's belly provides a clear view of the fetus and the placenta.

The transvaginal ultrasound is where a sterilized ultrasound probe is inserted into the vagina. This approach is often used in the first trimester of pregnancy to visualize the cervix, the uterus, gestational sac, embryo and other deep pelvic structures.

Transabdominal ultrasound:

The procedure

For women undergoing the transabdominal ultrasound, they're asked to come with a full bladder. The doctor will usually advise them to drink lots of water (approximately one to two quarts) one hour prior to the procedure. This will help make the various fetal parts easier to distinguish by moving the intestines out of the way.

A lubricating gel (which helps conduct the sound waves) is applied to the abdomen, then a probe is placed over the gel and moved around on the abdomen. The ultrasonographer can video a moving image or freeze a picture for permanent records.

This procedure takes approximately 10 to 30 minutes.