In societies where many girls marry at an early age, couples should delay the first pregnancy until at least the age of 18. For health reasons alone, no girl should become pregnant before the age of 18. A woman is not physically ready to begin bearing children until she is about 18 years of age. Babies born to women younger than 18 are more likely to be born too early and to weigh too little at birth. The birth itself is likely to be more difficult.
Babies born to mothers who are too young are also much more likely to die in the first year of life.
The risks to the mother's own health are also greater. After the age of 35, the health risks of pregnancy and childbirth begin to increase again. If a woman is over the age of 35, and has had four or more previous pregnancies, then another pregnancy is a serious risk to her own health and that of her unborn child. For the health of both mothers and children, parents should wait until their youngest child is at least two years old before having another baby. Children born too close together do not usually develop as well, physically or mentally, as children born at least two years apart.