Prenatal ultrasounds are routine for monitoring fetal development. These scans use sound waves to create images of the baby, providing insights into their growth and well-being. Expectant parents often look forward to these appointments, as they offer a first glimpse of their developing child and can answer many questions about the pregnancy.
The 13-Week Ultrasound Explained
The 13-week ultrasound, also known as the “nuchal translucency (NT) scan” or “first-trimester screening,” is performed between 10 and 13 weeks of gestation. Its primary purpose is to assess early fetal development and screen for certain chromosomal conditions.
This timing allows the nuchal translucency measurement, a fluid-filled space at the back of the fetal neck, to be assessed. The scan also confirms gestational age, which is more accurate in the first trimester, and establishes a precise due date. The procedure is non-invasive, with a sonographer guiding a transducer over the abdomen to display real-time images.
Is it Internal or External?
A 13-week ultrasound is typically performed transabdominally. During this procedure, gel is applied to the abdomen, and a handheld transducer is moved across the skin to capture images of the fetus. This external approach is sufficient at this stage because the uterus has grown larger, and a full bladder improves visibility by pushing the uterus higher into the abdomen.
However, a transvaginal (internal) ultrasound may be necessary at 13 weeks. This method involves inserting a thin transducer into the vagina, providing more detailed images because the transducer is closer to the pelvic organs and the fetus. Reasons for an internal scan include a retroverted uterus, maternal body habitus making external imaging difficult, poor image clarity from a transabdominal view, or suspected early pregnancy complications requiring precise anatomical detail.
What the 13-Week Ultrasound Reveals
The 13-week ultrasound provides diagnostic information. It confirms the fetal heartbeat, indicating pregnancy viability. The scan also determines the baby’s size by measuring the crown-rump length (CRL), which refines the estimated due date.
The scan includes the nuchal translucency measurement. This measurement, combined with blood tests, screens for the risk of chromosomal abnormalities like Down syndrome. Beyond screening, the sonographer evaluates the structural development of major organs, including the heart, brain, and limbs. The presence of multiple fetuses is also confirmed, and the health and position of the placenta, umbilical cord, and amniotic fluid levels are assessed.