Parturition (Birth) in Human

Introduction of Parturition 

• Humans are viviparous, as they give birth to their young ones. Parturition is the process of giving birth to a baby.
• The physical activities involved in parturition, like uterine and abdominal contractions, dilation of the cervix, and passage of the baby, are collectively called labor.
• Labor is accompanied by localized sensations of discomfort or agony, called labor pains.
• Parturition is controlled by a complex neuroendocrine mechanism. Signals arise from the fully formed fetus and placenta, causing mild uterine contractions. It is accompanied by a rise in the estrogen-progesterone ratio and an increase in oxytocin receptors in the uterine muscles.
• These factors cause vigorous contractions of the myometrium of the uterus at the end of pregnancy.
• The fully developed fetus gives signals for the uterine contractions by secreting
• Adrenocorticotropic Hormone (ACTH) from the pituitary and corticosteroids from the adrenal gland.
• This triggers the release of oxytocin from the mother's pituitary gland, which acts on the uterine muscles of the mother and causes vigorous uterine contractions.
• This leads to the expulsion of the baby from the uterus. Parturition involves the following three steps: 

This leads to expulsion of the baby from the uterus. It involves the following three steps: 

1. Dilation stage: 

• Uterine contractions begin from top, forcing the baby towards the cervix. Oxytocin induced uterine contractions become stronger due to stimulatory reflex.  

•  As the baby is pushed down in the uterus, its head comes to lie against cervix. Cervix gets dilated. The vagina also shows similar dilation.  

• This stage of labour can normally last upto few hours. It ends in rupturing of amniotic membrane of foetus.  

2. Expulsion stage: 

• The uterine and abdominal contractions become stronger. In normal delivery, the foetus passes out through cervix and vagina with head in forward direction.  

• It takes 20 to 60 min. The umbilical cord is tied and cut off close to the baby’s navel.  

Parturition 

After birth: 

After the delivery of the baby the placenta separates from the uterus and is expelled out as “after birth”, due to severe contractions of the uterus. This process happens within 10 to 45 minutes of delivery. 

1) Twins - Two embryos develop simultaneously in the same uterus and thus two offsprings are delivered simultaneously. Such offsprings are called as twins. Many couples have twins. There are types of twins

i.  Fraternal (Dizygotic) Twins:  

• When two oocytes are released from the ovary of woman and both oocytes are fertilized by two separate sperms and thus two zygotes are formed.  

• Two embryos are formed from those two zygotes and both of those embryos are separately implanted in the uterus and thus dizygotic twins are delivered after complete development. Such twins are genetically different and may be same of different by gender. 

ii.  Identical (Monozygotic):  

• Monozygotic twins are formed from single embryo. During early period of embryonic development (within 8 days of zygote formation), cells of that embryo divide into two groups.  

• Those two groups develop as two separate embryos and thus monozygotic twins are formed. Such twins are genetically similar to each other.  

• Due to this, such twins are exactly similar in their appearance and their gender is also same i.e. both will be either boys or girls.  

 iii.  Conjoined twins (Siamese twins): 

• In case of monozygotic twins, if the embryonic cells are divided into two groups 8 days after the zygote formation; there is high possibility of formation of conjoined twins (Siamese twins).  

• Such twins are born with some parts of body joined to each other. Some organs are common in such twins.

2. More than two - The triplets, Quadruplets:

• Triplets, quadruplets, and higher-order multiples are births that result from a single pregnancy.
• These multiples might consist of both fraternal and identical siblings.  

3. Test tube babies (IVF)

• In this technique, fertilization is brought about in the test-tube and the embryo formed is implanted in uterus of woman at appropriate time.
• IVF technique is used for having the child in case of those childless couples who have problems like less sperm count, obstacles in oviduct, etc.