An ultrasound, also known as sonography, is a non-invasive medical imaging technique that uses high-frequency sound waves to create pictures of internal body structures. During pregnancy, obstetric ultrasounds are widely used to monitor the developing pregnancy. This technology allows healthcare providers to visualize the pregnancy without using radiation, making it a preferred method for prenatal monitoring.
Timing of Early Pregnancy Ultrasounds
The earliest point an ultrasound might be performed in pregnancy is typically around 5 weeks from the last menstrual period (LMP). At this stage, a transvaginal ultrasound, which involves inserting a small probe into the vagina, is generally used because it provides clearer images compared to an abdominal ultrasound. While a gestational sac, the fluid-filled structure where the embryo will grow, can often be seen by 4.5 to 5 weeks with a transvaginal scan, the embryo itself may not be immediately visible.
Some providers schedule an early ultrasound between 6 and 8 weeks, especially if medically indicated. If a scan is performed too early, around 5 weeks, and the expected structures are not yet visible, a follow-up ultrasound is often recommended a week or two later to confirm progression. The timing of the first ultrasound can vary based on individual circumstances and the healthcare provider’s protocol.
Purposes of Early Pregnancy Ultrasounds
Early pregnancy ultrasounds serve several important objectives. One primary purpose is to confirm the pregnancy and ensure it is located within the uterus, helping to rule out an ectopic pregnancy, a potentially life-threatening condition where the fertilized egg implants outside the uterus. These scans also help in accurately determining the gestational age by measuring the embryo, to provide a more precise estimated due date.
They also assess viability by detecting a heartbeat, a reassuring sign of development. Early scans can identify if there is more than one fetus, such as twins or triplets. For individuals experiencing symptoms like pain or bleeding, an early ultrasound can help investigate potential complications like miscarriage.
What Early Ultrasounds Show
At 5 weeks gestation, a transvaginal ultrasound can typically show the gestational sac, a small, dark, fluid-filled area. Shortly after, around 5.5 to 6 weeks, the yolk sac, a small white circle within the gestational sac, often becomes visible. The embryo itself may also be seen as a tiny object around 5.5 to 6.5 weeks.
By 6 to 7 weeks, the fetal pole becomes more distinct, and a flickering heartbeat can often be detected. At 7 weeks, the embryo measures approximately 10mm from crown to rump, and the heartbeat is usually clearly present. As pregnancy progresses to 8 weeks, the ultrasound images begin to show increased detail, with the heart rate clearly accessible and the beginnings of limb buds becoming apparent.
Safety of Early Pregnancy Ultrasounds
Diagnostic ultrasounds are generally considered safe for both the pregnant individual and the developing fetus when performed by trained professionals. Unlike X-rays, ultrasounds use high-frequency sound waves rather than ionizing radiation. Used for decades, current evidence suggests no known harmful effects.
However, ultrasounds should only be performed when medically indicated. While diagnostic ultrasound does not pose a significant thermal risk, particularly in early pregnancy, some studies note uncertainties regarding non-thermal effects. Healthcare providers ensure that acoustic output levels are kept low and within safe limits during the scan. Patients should discuss any concerns with their healthcare provider.