Fetal development and birth

Fetal development

Fertilisation happens when an egg cell meets with a sperm cell and joins with it. The fertilised egg divides to form a ball of cells called an embryo. The embryo attaches to the lining of the uterus. It begins to develop into a fetus and finally into a baby.

Development of the fetus

Shows the placenta, uterus, fetus, umbilical cord, amniotic fluid, cervix and vaginaA fetus develops in the uterus into a baby ready to be born

The fetus relies upon its mother as it develops. These are some of the things it needs:

  • protection against knock and bumps, and temperature changes
  • oxygen for respiration
  • nutrients (food and water)

The developing fetus also needs its waste substances removing.

The fetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion.

The placenta

The placenta is an organ responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the fetus by the umbilical cord.

The mother's blood does not mix with the blood of the fetus, but the placenta lets substances pass between the two blood supplies:

  • oxygen and nutrients diffuse across the placenta from the mother to the fetus
  • carbon dioxide and other waste substances diffuse across the placenta from the fetus to the mother
Two intertwined foetus' blood vessels connect to villi. Villi surrounded by placental membrane which in turn is cushioned in intervillous space. Mother's blood vessels are also connected to the villi.The blood of the mother and fetus do not mix, but substances diffuse across the placenta

The mother’s lifestyle can affect the developing fetus. For example, smoking reduces the amount of oxygen in the bloodstream. This can lead to low birth weight and premature birth (when a baby is born too soon). Drinking alcohol during pregnancy can harm the developing baby’s nervous system, especially its brain.


It takes about 40 weeks for a baby to develop in the uterus. This time is called gestation. After this, the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract. Waves of muscle contraction push the baby out of the mother's body through the vagina.

Premature baby in incubator
Some babies are born too early and need to put into a warm incubator, where they may also be helped to breathe