Page 43 - 33Elctronic Book (3) Normal Labor

➢ Psychological state of the woman and her personality: knowledgeable

and relaxed woman, who is actively participating in the birth process,
usually experiences shorter, less intense labor. The process of labor also
depends on woman's pain threshold.

Theories of Onset of Labor

1 – Prostaglandins :

* Can induce uterine contractions.

* They are formed in the decidua and membranes.

* Their level increases near term.

2 – Progesterone withdrawal:

* Progesterone supports pregnancy, it decreases the frequency of uterine
contractions . .

* A drop in progesterone level-with subsequent onset of labor could be proved only
in some animals, not in humans.

3 – Estrogen/ Progesterone:

- Estrogen helps the initiation of uterine contractions.

- Estrogen level increases near term.

4 – Estrogen-Oxytocin:

* Estrogen increases the myometrial receptors to Oxytocin “indirect effect’’.

* Oxytocin causes uterine contractions.

5 – Fetal suprarenal:

- The increase production of estrogen by the placenta near term is due to an
increase in the level its precursor: DHEAS. (dehydro- epiandrosterone sulfate)

which is produced in increased amounts by the fetal suprarenal near term with
fetal maturity.

- Anencephaly is a congenital anomaly in which the fetal vault of the skull is
absent, the brain and pituitary are atrophied. (Incompatible with life).

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