A baby develops in the uterus, or womb – a hollow, muscular organ in the mother’s abdomen. The period of development in the uterus lasts about nine months in most cases. During this period, development is more rapid than at any time after birth.
For a baby to develop, sperm from the father must unite with an egg from the mother. This union of a sperm and an egg is called fertilisation. It produces a single cell called a fertilised egg. By a series of remarkable changes, the fertilized egg gradually develops into a baby.
By the fifth month of pregnancy, fine hair called lanugo covers the body of the foetus. Lanugo disappears late in pregnancy or shortly after birth. Hair also disappears on their head.
From the ninth week of pregnancy until birth, the developing baby is called a foetus. In the first three months of this period, the foetus increases rapidly in length. It grows about 5 cm in each of these months.
In later months of pregnancy, the most striking change in the foetuses is in their weight. Most foetuses gain about 700 grams in both the eighth and ninth months of pregnancy. The mother can feel movements of the foetus by the fifth month of pregnancy. The eyelids open by the 26th week of pregnancy.
By the 28th week, the fingernails and toenails are well developed. Until the 30th week, the foetus appears reddish and transparent because of the thinness of its skin and lack of fat beneath the skin. In the last six to eight weeks before birth, fat develops rapidly and the foetus becomes smooth and plump.