Calgary Baby Guide 2023-2024

TYPES OF
ULTRASOUNDS IN
PREGNANCY
A GUIDE FROM A MATERNAL-
FETAL MEDICINE SPECIALIST
Prenatal ultrasounds are considered an essential part of obstetrical care these days. Although they
provide a special window into the womb, allowing to see the baby before birth, they are also medical
exams either leading to reassurance, and for a minority, to uncertainty and changes of plans.
Here is a brief chronological overview of the several types of ultrasounds in pregnancy.
Dating is traditionally based on a full term 40-week (wk.) pregnancy.
Early viability and dating
The first ultrasound can be done from 5 wk. but is ideally done between 7-10 wk. for best dating
accuracy. The earlier this ultrasound is done, the higher the chance that an internal vaginal probe is used to
be able to image the pregnancy, in addition to an abdominal approach (over the lower abdomen with a
full bladder). This ultrasound can locate the pregnancy (inside the uterus versus ectopic), can assess
viability, and number of embryos. Measuring the length of the embryo provides a solid dating of the
pregnancy with an error range of 3-8 days, making it more accurate than using the last menstrual period
date in some cases.
The 11-13 wk. scan
The 11-13 wk. scan can provide an accurate dating if there was no dating scan performed prior. It has
also been called the “NT scan” in the past, as it was mostly used to look at the fetal Nuchal Translucency
(NT); a thin fluid layer at the back of the neck of the fetus at this stage. The NT is used to screen for certain
genetic conditions and cardiac malformations. Increasingly, with the advances in technology, the early
look into the fetal development has allowed the review of early anatomy and the health of the pregnancy,
beyond just the NT. This scan can detect some malformations, allowing families to decide earlier if they
want to have additional testing and surveillance. This ultrasound can also be used to screen for the risk of
developing pre-eclampsia* in the third trimester, but unfortunately this is not yet available everywhere.
*Pre-eclampsia is a hypertensive illness developing in pregnancy that can have sudden onset and cause
issues both for mom and baby.
22 • www.modernmama.com | CALGARY | A RESOURCE GUIDE | 2023/2024 Edition