The first ultrasound in an early pregnancy is often a source of anticipation and anxiety. For those at seven weeks of gestation, the question of whether the scan will be internal or external is common. An ultrasound uses high-frequency sound waves to create a real-time picture of internal structures. At this stage, the seven-week ultrasound is nearly always performed internally, a method known as a transvaginal ultrasound, to ensure the clearest possible view of the tiny embryo.
The Procedure at Seven Weeks: Internal (Transvaginal) Ultrasound
This internal method is formally called a transvaginal ultrasound (TVUS) and is a routine procedure in early pregnancy. The patient is typically asked to lie on an examination table, often with the knees bent, similar to a standard gynecological exam. You will be asked to empty your bladder before the scan, as an empty bladder can improve the clarity of the images.
The sonographer uses a thin, wand-shaped instrument called a transducer, which is slightly larger than a tampon. This transducer is covered with a protective sterile sheath and lubricating gel before being gently inserted into the vagina. The entire procedure is generally quick, lasting around 15 to 20 minutes. While not painful, you may feel some pressure or mild discomfort. The transducer is carefully moved to capture images from different positions, providing a comprehensive view of the uterus and its contents.
Why Transvaginal Imaging is Necessary in Early Pregnancy
The transvaginal approach is necessary because of the small size of the embryo and its deep location within the pelvis. At seven weeks, the uterus is still situated low inside the pelvic cavity, and the developing embryo measures only about five to ten millimeters in length. The external, or transabdominal, method would require the sound waves to travel through layers of skin, fat, and muscle, which significantly degrades the image quality.
By placing the transducer inside the vaginal canal, the probe is positioned much closer to the target organs, including the uterus and the gestational sac. This proximity allows the sonographer to use higher frequency sound waves. Higher frequency waves provide superior image resolution and detail, which is necessary to visualize structures that are only millimeters in size. This clarity is not possible with the lower frequency sound waves used in an external abdominal scan.
What the Seven-Week Ultrasound Confirms
The primary focus of the seven-week scan is to confirm a healthy and progressing pregnancy by gathering specific clinical data. The scan provides several key confirmations:
- Fetal viability: The presence of a fetal heartbeat is confirmed, often visible as a rapid flicker. This activity is measured, typically ranging between 90 and 180 beats per minute.
- Location of the pregnancy: The scan ensures the gestational sac is correctly implanted inside the uterus, ruling out an ectopic pregnancy.
- Dating the pregnancy: The sonographer measures the embryo’s length, known as the Crown-Rump Length (CRL). This measurement establishes the estimated due date.
- Multiple gestation: The scan confirms whether there is a single embryo or signs of multiples by identifying the number of gestational sacs and heartbeats.
As the pregnancy progresses and the uterus rises out of the pelvis, subsequent scans will transition to the more familiar external, transabdominal method.