The heart of the fetus develops after one month of pregnancy and the beats can be heard using stethoscope. By the end of second month, limbs and digits develop. By the end of third month or the first trimester, all the major organs are formed. By fifth month, fetus starts to move around. hair appears on head. By the end of second trimester, body is covered by fine hair, eye lids separate and eye lashes are formed. By the end of 9 months, the foetus is fully developed and ready to be delivered. This period of 9 months or 38 weeks of development of the zygote to the fully developed baby is called gestation period.