Biological Factors of Birth

1. Heredity: It is said that heredity affects fecundity and fertility (the daughter many give birth to twins if her mother had given birth to twins) but there is no significant basis of empirical study on it. However, infirmity in reproductive system and STIs adversely affect the fertility.
2. Age: Human being attain fecundity only after specific age. Women cannot conceive and give birth before maturity and after reproductive span. Generally, women attain fecundity after menarche in 14-15 years and they are fecundable till about 49 years. The women in 20-24 and 25-29 years are highly fecundable. The reproductive period is 34 years from 15 to 49 years. The later the marriage takes place, the shorter will be the reproductive span and vice versa. As a result of early marriage, the span remains longer for child-bearing. Thus, the fertility remains high. Male's fecundity remains longer than female.
3. Health: Health is wealth of person. The healthy people have higher fecundity as their proper physical development including reproductive system. Morbid people have less fecundity comparatively healthy ones.
4. Ovulation: There are two ovaries either side of uterus in women. After onset of menstruation, an ovum is released alternatively from both ovaries every month. At the mid-point (14th day) of menstruation cycle (MC), ovulation (releasing a matured ovum from ovary) takes place. The ovum comes to fallopian tube and stays there. If the sexual intercourse takes place during that time, the conception takes place with the penetration of the ovum of female by a sperm of male. Otherwise, the conception does not take place in other time.
5. Lactation: The breast feeding (lactating) mother conceives later because her ovulation is delayed and menstruation takes place later. Lactation also causes the contraction of uterus. It reduces the possibility of conception. The period from child birth to at least 6 months is called lactational amenorrhea period. Therefore, lactation has direct relationship with human fertility.
6. Miscarriage: we cannot say that every fecund woman can give live birth. For this, they should give the birth alive. Due to various causes, some of the pregnancies are terminated prior to the expected date of delivery without viability of life. This is called miscarriage or spontaneous abortion.