A 7-week ultrasound is a common early pregnancy scan performed to confirm pregnancy, check viability, and establish an accurate due date. It provides a first glimpse into the developing pregnancy and helps healthcare providers gather important information.
The Developing Embryo
At 7 weeks gestation, the embryo typically measures about 9 to 10 millimeters (mm) from crown to rump, roughly the size of a blueberry or a coffee bean. It is C-shaped or tadpole-like, with a disproportionately large head due to rapid brain development.
Early facial features begin to form, including depressions for the eyes, ears, and nostrils. Tiny limb buds, appearing somewhat like paddles, are also visible. While detailed features like fingers and toes are not yet distinct, fundamental structures are emerging. A key visual sign at this stage is a flickering motion within the embryo, indicating a beating heart.
Key Visual Markers
Beyond the embryo, a 7-week ultrasound reveals other structures that indicate pregnancy development.
The gestational sac appears as a dark, fluid-filled circle surrounding the embryo, an early sign of pregnancy. This sac protects and cushions the developing embryo, providing an environment for its early growth. Its presence confirms an intrauterine pregnancy, meaning the embryo has implanted within the uterus.
Adjacent to the embryo, within the gestational sac, a small, circular structure known as the yolk sac is also visible. The yolk sac provides nourishment to the embryo in these early weeks, before the placenta fully takes over this role. It typically measures about 3 mm at 7 weeks. Visualization of both the gestational sac and an appropriately sized yolk sac indicates healthy early pregnancy development.
Information Gained From the Scan
A 7-week ultrasound provides diagnostic information beyond visual confirmation.
A primary focus is confirming a heartbeat, which appears as a rapid flicker on the screen. This cardiac activity indicates the pregnancy’s viability, with the heart rate typically ranging between 90-110 beats per minute at 6-7 weeks, and increasing to 120-160 beats per minute by 7 weeks.
The scan also measures the embryo’s crown-rump length (CRL), the length from the top of its head to its bottom. This measurement is accurate for determining gestational age and establishing an estimated due date, especially at this early stage.
The ultrasound confirms the pregnancy’s location within the uterus, ruling out ectopic pregnancies where the embryo implants outside the uterus. In cases of multiple pregnancies, the scan can identify more than one embryo, often by detecting multiple gestational sacs or yolk sacs, providing early confirmation of twins or other multiples.