https://www.chison.com/news/a-case-report-intelligent-womens-healthcare-solution.html

Ultrasound findings of normal placenta

Ultrasound can show the placenta as early as 6 weeks of pregnancy (transvaginal ultrasound) or 10 weeks of pregnancy (transabdominal ultrasound), showing a thin ring, and hypoechoic around the embryo. At the 12th and 13th weeks of pregnancy, a Doppler ultrasound can show the chorionic blood flow. At 14-15weeks of gestation, the placenta is fully developed, which is usually hyperechoic in nature. In the second trimester, the placenta gradually matures and becomes larger, showing a more homogeneous hyperechoic, in which there may be a low echo area with unclear boundaries,  which is the placental lake. In late pregnancy, a Doppler ultrasound can show abundant blood flow in the placenta.