Factors responsible for parturition

You might wonder what exactly happens inside your womb that baby suddenly wants to come out. Just think about it the baby was happy in your womb for 9 months then what provokes him to come outside and see the worlds with their own eyes. In this article, you will learn the various factors responsible for the parturition. Parturition is the term used to define the birth of the baby. Towards the end of the pregnancy, the womb ( uterus) becomes so excited that it develop systematic rhythmical contraction, that finally expelled the baby outside the womb. There are two major reasons for such a change in uterine behaviour:

  1.   Hormonal changes in pregnant women.
  2.   Mechanical changes in the body of pregnant women. 

Hormonal changes in pregnant women

i) Increase in the ratio of estrogen and progestogen hormone – 

As we know pregnancy begins which the change in hormonal concentration and their ratio in the body of the pregnant women. With the pregnancy, there is an increase in the secretion of estrogen and progestogen.  The role of progestogen is to reduce or better word will be inhibiting the contraction in uterine which helps to prevent the expulsion of the fetus, while estrogen, on the other hand, increases the contraction. During the time of pregnancy, they both secrete in high quantity but from the seventh month onwards the secretion of estrogen increases further while progestogen remains constant. This ratio of estrogen and progestogen further enhance at 9th month which results in contraction of uterine. 

ii) The rise in the level of Oxytocin Hormone – there are strong reasons to believe that Oxytocin is responsible for the contraction of uterine. It has been observed that during the time of labor the level of Oxytocin is increased even the receptor of Oxytocin in uterine wall increases. The experiments on an animal show that the stretching of the uterine cervix, as occurs in pregnancy can cause neurogenic reflex which increases the secretion of Oxytocin. 

iii) Effect of fetal hormones on uterine- the fetus’s pituitary gland also secretes the number of hormones which results in contraction of uterine. These hormones are Oxytocin; Cortisol along with this fetal membrane also secretes the prostaglandins in high concentration which further excite the uterine wall. 

Mechanical changes in the body of pregnant women. 

 There is a number of mechanical changes along with the hormonal changes that found to play an important role in uterine contraction. 

i) Stretch of the uterine musculature – the fetal movement in the uterine causes the intermittent stretch in the smooth muscles of uterine musculature which results in contraction of uterine. It has been observed that the twins are born 19 days earlier than a single child; however, this fact explains the importance of stretch of uterine muscles because of fetal movements. 

ii) Stretch of the cervix – the exact mechanism of the stretch of the cervix is not known yet but it has been suggested that stretching of irritation cause of stretching of cervix or movement of baby’s head stimulate the reflexes to the uterine wall which results in contraction. 

iii) Labor contraction – throughout the pregnancy duration, the body goes with systematic rhythmic contraction. This periodic contraction is known as Braxton Hicks contraction. However, this contraction becomes stronger towards the end of pregnancy. Then this contraction suddenly becomes too strong that the baby is forced towards the birth canal. This sudden contraction in muscles is known as labor.

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