|
The fertilized single-cell egg multiplies into two, then four cells, and it carries on multiplying so that by about day seven, when it reaches the uterus, it has grown into a ball of over 100 cells with a fluid-filled cavity. This ball, called a blastocyst, has two layers: the outer one becomes the placenta, while the inner one forms the embryo, which develops into your baby.
The embryo is made up of three layers of tissue, each of which forms separately. The outer layer develops into the nerves and skin; the middle layer forms the bones, cartilage, muscles, circulatory system, kidneys, and sex organs; and the inner layer becomes the respiratory and digestive systems.
The placenta is the unborn baby's life-support system. It is attached to the lining of the uterus and separates the developing baby's circulation from its mother's. It allows oxygen and food, as well as protective antibodies, to pass from the mother along the umbilical cord to the baby. The placenta isn't fully formed until the end of the 12th week of pregnancy when it is able to take over the production of the pregnancy hormones, oestrogen and progesterone, from the ovaries.
Within the uterus, the embryo is contained in the amniotic sac. This is filled with fluid in which the developing child will float until birth. The amniotic fluid offers protection from any external pressures.
The baby's sex after fertilization
A child's sex is determined by the father's sperm at the time of conception. Sperm carry either an X or Y chromosome while the egg has only an X chromosome. If a Y-chromosome sperm fertilizes the egg, the baby will be a boy. If the sperm carries an X chromosome, the baby will be a girl.
|
