The Third Trimester Ultrasound: What Is It And Why Has My Doctor Ordered It?

The home stretch! You are almost there!

Why am I having this ultrasound?

It is quite common to have an ultrasound in the third trimester of pregnancy, and this can be for a variety of reasons. The third trimester is defined as taking place from the 27th week of pregnancy and onward, and this is a stage when the fetus is growing rapidly and changing positions. Many obstetrical care providers like to include an ultrasound in the third trimester as a type of “check-in.” This is generally a very welcome appointment from the point of view of the woman and family, as it has likely been quite some time since the detailed ultrasound that took place at approximately 19 weeks gestation. There are many reasons to have an ultrasound at this later stage of pregnancy. The goal of such an exam is, generally, to ascertain the position and presentation of the fetus, determine the relative size and growth, document the amount of amniotic fluid present, and to assess the movements and tone of the fetus to offer insight into the state of well-being. Having an ultrasound in the third trimester can elucidate valuable information for the medical care provider and offer reassurance to the patient. It is also a great opportunity to get a sneak peek of those sweet chubby cheeks!

What to expect during your ultrasound?

You have reached yet another milestone in your pregnancy! You no longer need to fill your bladder for the ultrasound appointment if you are at, or over, 28 weeks gestation, hooray! Instead, we request that you please have a snack or meal within 30 minutes of your appointment. We will be assessing the activity of your baby throughout the exam, and if you have not eaten recently this can affect the amount of movement that the baby will display.

During this exam you will be given an extra pillow to increase your comfort level while lying down. You will not be lying flat, but rather at a comfortable incline. There is also a patient viewing monitor available to allow you to watch along with what the technologist is seeing and imaging. This exam typically takes between 15 and 30 minutes.

As with previous ultrasounds there will be an interrogation of the placenta, a documentation of the fetal position in the uterus, measurements done of the fetal biometry (head, belly, and leg bone), a quantification of the amniotic fluid volume, and an observation of the fetal heart motion and rate. Some additional anatomy will be imaged when possible, including the face . You will be offered a complimentary photo after the exam as a keepsake. Whether or not the image is one of the face or profile is completely up to your baby! They must cooperate and be in the right position in order to obtain the image.

At the end of the exam the technologist will be able to communicate the estimated fetal weight with you. This is an estimate based on the measurements taken during the ultrasound.

Finally, the sonographer will leave briefly to review the images with the on-site Beam Physician. This is normal and to be expected. When they return, you will be all set to go. Your doctor will receive the report following your appointment, and if follow up is needed or desired that can be booked as well.