Section 3.1 Prenatal development

The embryonic stage begins after the fertilized egg attaches to the mother’s uterine wall and lasts from about the 2nd to the 8th week after conception. This is a critical period of development, as the foundations of all major body systems are established.

By week 4, the placenta is fully formed. It serves a vital role by delivering oxygen and nutrients from the mother to the developing baby while also removing waste products. During this time, organ development, or organogenesis, begins, with the formation of the skin, muscles, nerves, heart, and other organs.

A heartbeat can typically be detected around week 4. The baby also starts to form lungs and small limb buds, which will later develop into arms and legs. As the stage progresses, early shapes of fingers, toes, eyes, nose, mouth, and ears become visible, and the nervous system starts to develop.

By the end of the embryonic stage, around week 8, the baby’s major organs have formed, and bones begin to grow, signaling the transition into the next phase of prenatal development which is the fetal stage.