After the occurrence of menarche, woman is still underdeveloped in the body and genitals, but she is able to get pregnant. The organ for pregnancy and delivery is the uterus. The mechanism of pregnancy lies in the combination of the essence from a man and a woman. If a woman is well developed in kidney essence with free flow of the conception vessel and fullness of the thoroughfare vessel,she will be easy to get pregnant when she has sexual intercourse with a man. The development and growth of fetus in the uterus were vividly described in some of the ancient medical canons. 

After pregnancy, qi and blood accumulate in the thoroughfare vessel and conception vessel for providing nourishment for the fetus. That is why menstruation stops.But at the early stage of pregnancy, the uterus only stores essence and never excretes. Since the fetus is growing in the uterus and blood and qi are accumulating in the uterus, bi in the thoroughfare vessel is easy to flow upwards. If the liver blood in gravida is insufficient, it will lead to relative deficiency of liver yin, relative hyperactivity of liver yang because blood accumulates in the uterus to nourish the fetus. The liver governs thoroughfare vessel, simultaneous upward flow of liver qi and thoroughfare vessel qi frequently leads to attack on the stomach. That is why at the early stage of pregnancy there are morning dizziness, lassitude, somnolence, preference for sour taste, nausea and vomiting which are physiological changes and usually disappear in three months. 

Since blood accumulates in the uterus to nourish the fetus, it is already deficient during pregnancy. Hemorrhage during delivery further worsens blood deficiency. Asthenia of yin fails to keep yang inside and leads to leakage of yang,bringing about such symptoms like slight fever, aversion to cold and spontaneous sweating which will disappear automatically after yin and yang are balanced. Besides,blood asthenia and profuse sweating may cause constipation because the consumption of body fluid will deprive the intestines of proper moistening. 

   

After delivery, there will be secretion of nfilk. Usually during the pregnancy, the breasts are gradually enlarged, the areola of mamma is deepened and foremilk is secreted. The milk is transformed from blood and produced by gastric qi. Since blood, propelled by lung-qi, is transformed into milk and stops flowing into the uterus,there is no menstruation during breast feeding period.