Ultrasounds are a routine and generally safe aspect of prenatal care, particularly in the early stages of pregnancy. They monitor the developing pregnancy and provide valuable information. An early ultrasound can confirm a pregnancy, check for potential complications, and help determine the gestational age of the embryo. They offer a glimpse into the initial stages of development.
The 7-Week Ultrasound Method
At seven weeks of gestation, a transvaginal ultrasound is the preferred method for viewing the developing embryo. This internal procedure involves inserting a small, wand-shaped transducer into the vaginal canal. The transvaginal approach is chosen because the embryo is still very small, measuring approximately 9-10 millimeters (about the size of a blueberry or a grain of rice), and is situated deep within the pelvis. Placing the transducer closer to the reproductive organs allows for clearer and more detailed images than an external, transabdominal ultrasound.
While a transabdominal ultrasound, where a probe is moved across the abdomen, is common later in pregnancy, it is less effective at this early stage. Sound waves from an abdominal scan must travel through more layers of tissue and muscle, potentially resulting in less clear images of the tiny embryo. The transvaginal scan may cause some pressure, similar to a pelvic exam, but is generally not painful.
What the Ultrasound Reveals
A 7-week ultrasound provides insights into the early development of the embryo. The sonographer looks for the gestational sac, a fluid-filled sac surrounding the embryo, visible as a dark circle. Within this sac, the yolk sac, which provides nourishment to the embryo before the placenta fully forms, can also be observed. The fetal pole, the earliest visible sign of the embryo itself, appears as a thickened area attached to the yolk sac.
The presence of a fetal heartbeat is a key finding at this stage. While it may appear as a flickering light or a pulsating spot, the heart is beating at a rate between 90 and 110 beats per minute at 7 weeks. This heart activity indicates viability. Measurements, such as the crown-rump length (CRL), are also taken from the top of the embryo’s head to its bottom to help confirm gestational age and predict the due date. At 7 weeks, the embryo’s crown-rump length ranges from 5 to 12 millimeters.
Preparing for Your Appointment
Wear comfortable, loose-fitting clothing. A transvaginal scan typically requires undressing from the waist down. Arriving on time ensures a smooth check-in process and allows the medical team to stay on schedule.
For a transvaginal ultrasound, an empty bladder is preferred for comfort. Some clinics may request a partially full bladder for initial transabdominal viewing before proceeding with the internal scan. You should feel comfortable asking any questions you may have about the procedure or what to expect, as open communication with the medical staff is always encouraged.