At 5 weeks of pregnancy, your baby is still called an embryo, but development is moving at an astonishing speed. The embryo is about the size of a sesame seed and has a curved, tadpole-like shape. One of the most significant milestones this week is the early formation of the heart, which begins to develop as a simple tube and may start beating by the end of the week, although it’s usually too early to hear it on ultrasound. The neural tube continues to close and expand, forming the foundations o