Page 41 - 2023 Elctronic Book (3) Normal Labor_Neat

- 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).

- In These cases, the fetal suprarenal are not stimulated by ACTH and onset of

labor may therefore, be delayed.

6 – Uterine distension:

Near term, fetal growth continues and uterine growth becomes slower; the result is

increased distension of uterine muscles initiating uterine contractions. Preterm
labour may occur with early distension, e.g.: twins and polyhydramnios.

7 – Placental ischaemia:

- Resulting in lower production of oxytocin’s- an enzyme thought to be

responsible for oxytocin degradation-with subsequent rise in oxytocin level.
8 – Stretch of the lower-uterine segment:

By the presenting part near term may contribute to the onset of labor.

 Premonitory Symptoms and Signs of Labor:

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