Parturition and Lactation :
Parturition is the acts of expelling the full-term baby from the mother's uterus at the end of pregnany completed in about 280 days from the mother's last menstruation. However, in some cases it may very be several days or weeks. Most of the major organs are formed by the twelth week of pregnancy and in the rest of the gestation period the foetus grows. It is important that the baby be born when it is mature. The foetus signals that it is mature by secreting ACTH hormone from its pituitary. ACTH causes the release of corticosteroid hormones from its adrenal glands. These foetal hormones diffuse across the placenta and accumulate in the mother 's blood till they cause a decrease in progesterone production and an increase in the secretion of progesterone production and an increase in the secretion of prostaglandins. Reduced progesterone level allows the secretion of the hormone oxytocin by the mother's pituitary gland and ends the inhibitory effect on uterine muscles to contract and prostaglandins increase the force of the contractions. This provides force to expel the baby from the uterus, causing birth. The baby ready for birth is about 53 cm long and weight about 2.7 to 4.5 kg. His / her skin is blush-pink in all human races as pigment is made after exposure to sunlight.
Parturition involves forceful muscular contractions, called labour, of the uterine wall. The term is appropriate as it is a period of work at the expense of considerable energy. About two weeks before birth, the foetus normally settles head downward into the pelvic cavity. On the completion of gestation, labour starts. It causes labour pains. Parturition may be divided into 3 stages.
1. First stage (Dilation) : It lasts for about 12 hours. Regular peristaltic contractions of the uterine wall begin, passing from its top downward. These contractions move the foetus down towards the cervix which expands fully. Amnion and chorion rupture. The amniotic fluid passes out, lubricating the vagina. The foetal placenta is pulled out form the uterine wall, making the body free.
2. Second Stage ( Expulsion) : It lasts for about 20 minutes to one hour. The uterine contractions become more powerful and are accompanied by contractions of the abdominal wall. With these contractions the baby is gradually pushed outward thought the dilated cervix and vagina, with the head foremost, and is finally "delivered" (born) into the outside world, where it draws its first breath.
3. Third (Placental) Stage : It lasts for just 10-45 minutes after the infant's birth. Now the placenta, umbilical cord and foetal membrane are expelled by series of uterine contractions. These structures are referred to as the "after birth".
Further contractions of the uterus close the cervix and prevent excessive bleeding. Bleeding, throughout the process, is kept low by contraction of smooth muscle fibres of uterine blood vessels supplying the placenta.
Sometimes the foetus fails to come out and a surgical procedure, called Cesarean section, is needed. The baby is removed through a cut given in the mother's placenta.
Lactation :
Mammary glands start producing milk at the end of pregnancy by the process called Lactation. The milk produced during the initial few days of lactation is called colostrum which contains several antibodies. It helps in developing resistance for new born baby.