Ultrasound and Pregnancy: The First Trimester

When most people hear the term “ultrasound” one particular thought comes to mind: pregnancy. Every expectant parent loves a glimpse of who’s-to-come – and finding out which color to paint the nursery is a bonus for many!

However, ultrasound is far more powerful than simply providing in utero baby snapshots. Ultrasound has revolutionized the approach to pregnancy, giving information which can save lives – the baby’s or the mother’s or sometimes both. Ultrasound uses sound waves – not radiation – to produce images, so in trained hands it is safe to use at any time during pregnancy.

During the first trimester, ultrasound is used most frequently to confirm pregnancy (along with a blood test), to confirm the location of the pregnancy and to evaluate bleeding. In the first trimester, the ultrasound will likely involve images obtained through a distended bladder and a transvaginal exam.

Here’s what to expect:

First, you will be asked to come to the exam with a full bladder – we actually use the full bladder as a “window” through which we can view the pregnancy.

The first part of the exam with the bladder full will be done using a transducer across your belly to get a view of the uterus and your pelvis. This is most helpful in demonstrating the pregnancy location. Once these images are obtained, you will be able to empty your bladder and return for what is called a transvaginal ultrasound. This involves a small probe being placed into the vagina to image the pregnancy and pelvic structures. This transducer allows better depiction of the pelvic structures and will allow more detailed evaluation – this is used in the first trimester and occasionally later in pregnancy. In the first trimester when the pregnancy is so small, the transvaginal part of the study is often key. There is usually little or no discomfort with the transvaginal study.

The whole process will take about half an hour.

What can we see in the first trimester?

It depends on the age of the pregnancy. When first visualized, the pregnancy will be a small fluid filled sac. At around 6.5  weeks, the embryo is often seen as a small peanut shaped structure – heart beating away. By the end of the first trimester, you can distinguish the head, trunk and the limbs. Everything is small, so in general gender will not be determined. We will evaluate the age of the pregnancy and compare to what you should be; confirm that the pregnancy is in the uterus; count babies – twins anyone? – look for the heartbeat, which we can only see once the embryo is big enough (7 mm is the key embryo size to expect to see a heartbeat!); and look at the pelvic structures. Fetal anatomic detail is limited by the small size, but it is amazing what you can see!

We know having babies is stressful – and not always easy! We wish you all the best, and hope this helps explain the process of the first trimester obstetric ultrasound.

Originally published 3/20/14 on diagnosticimagingcenterskc.com.