An early pregnancy ultrasound uses sound waves to create images of the uterus and its contents. This scan confirms pregnancy, estimates the due date, and checks for healthy development. At five weeks, it is a very early stage, so what is visible is small and still developing. Understanding the limitations of what can be seen at this stage is important.
What’s Visible on a 5-Week Ultrasound
At five weeks, a transvaginal ultrasound is often used for the clearest images. This method involves inserting a lubricated wand into the vagina, allowing closer proximity to the uterus and better resolution of early structures.
The first structure identified is the gestational sac, appearing as a small, fluid-filled black circle within the uterus. This sac measures approximately 2 to 3 millimeters in diameter and grows by about 1.13 mm per day. Its presence confirms an intrauterine pregnancy, distinguishing it from a potential ectopic pregnancy.
Shortly after the gestational sac becomes visible, the yolk sac appears as a small, bright ring inside it. The yolk sac plays a role in providing nutrients to the developing embryo before the placenta forms and contributes to early blood cell production. Visualizing both the gestational sac and yolk sac is a positive sign of progression.
The fetal pole, the earliest visual evidence of the embryo, can be seen as a small, thickening area adjacent to the yolk sac at the end of five weeks. It may resemble a grain of rice, measuring only 1 or 2 millimeters. A heartbeat might occasionally be detected as a flicker around 5.5 to 6 weeks, but it is more common around six to seven weeks of pregnancy.
Understanding Variations and Next Steps
An ultrasound at five weeks may show variations from typical expectations, which can be a source of concern. One common reason for fewer visible structures is that the gestational age might be slightly miscalculated, meaning the pregnancy is actually earlier than initially thought. This can occur if the date of the last menstrual period was inaccurate or if ovulation happened later than anticipated, leading to lower human chorionic gonadotropin (hCG) levels, which influence what is visible on the scan.
If only a gestational sac is seen, or nothing is visible, it can indicate a very early pregnancy that has not yet developed enough to show more structures. It might also point to a chemical pregnancy or an early miscarriage. Less commonly, the absence of expected structures could raise the possibility of an ectopic pregnancy, where the embryo implants outside the uterus.
When findings are inconclusive or do not align with expectations at five weeks, a follow-up ultrasound is frequently recommended. This subsequent scan, usually performed in 7 to 10 days, allows medical professionals to observe for continued growth and development of the gestational sac, yolk sac, and fetal pole. Development progresses rapidly, and a second look can provide much clearer information regarding the pregnancy’s viability.