The foetal membranes are specialized structures that surround and protect the developing foetus during pregnancy. They provide a protective environment, facilitate the exchange of substances, contribute to nutrition and immunity, and play an important role during labour and delivery. In maternal health nursing, knowledge of the foetal membranes is essential for understanding normal pregnancy, amniotic fluid, rupture of membranes, complications such as premature rupture of membranes, and the mechanism of labour. The principal foetal membranes are the amnion and chorion. Other structures closely associated with the foetal membranes include the yolk sac, allantois, and decidua, although the amnion and chorion constitute the major membranes surrounding the foetus in later pregnancy. The amnion is the innermost and most delicate foetal membrane. It directly surrounds the amniotic cavity and the foetus. It is a thin, transparent, avascular membrane composed mainly of epithelial cells and connective tissue. The amnion produces and helps regulate amniotic fluid and provides a smooth surface around the foetus. As pregnancy advances, the amnion expands considerably and comes into close contact with the chorion. The amniotic cavity contains amniotic fluid, which is essential for normal foetal development. Amniotic fluid provides a cushioning effect and protects the foetus from mechanical injury. It permits free movement of the foetus, which is important for the normal development of muscles and bones. It also helps maintain a relatively stable temperature around the foetus and prevents adhesion of the foetus to the surrounding membranes. Amniotic fluid also contributes to the development of the respiratory and gastrointestinal systems because the foetus swallows and aspirates small quantities of the fluid during pregnancy. The chorion is the outer foetal membrane. It develops from trophoblastic tissue and extraembryonic mesoderm. The chorion surrounds the amnion and is closely associated with the placenta. Its outer surface initially develops numerous finger-like projections called chorionic villi. These villi are important in the formation of the placenta and facilitate the exchange of oxygen, nutrients, carbon dioxide and waste products between the maternal and foetal circulations. The chorion also has an important endocrine function because trophoblastic tissue produces hormones, particularly human chorionic gonadotropin during early pregnancy. During early pregnancy, the chorion is differentiated into the chorion frondosum and chorion laeve. The chorion frondosum is the villous portion that contributes to the foetal part of the placenta. The chorion laeve is the smooth portion where the chorionic villi largely disappear. As pregnancy progresses, the amnion and chorion become closely adherent and form the amniochorionic membrane. The amniochorionic membrane forms the major membrane surrounding the amniotic cavity in the later stages of pregnancy. Although the amnion and chorion are closely attached, they are not fused at the cellular level in the same way as a single membrane. Their separation may occur under certain pathological conditions or during the process of membrane rupture. The yolk sac is an early extraembryonic structure that has important functions during the initial stages of embryonic development. It contributes to early nutrition before the placenta becomes fully functional. It is also an important site