Page 40 - 2023 Elctronic Book (3) Normal Labor_Neat

• Characteristics of uterine contractions:

• Frequency or interval: The period between the start of one contraction and
the start of the next one.

• Duration: The period between the start of one contraction and its end.
• Intensity: The power or strength of the contraction.

• Phases of contraction: Each contraction has three phases:
A-Increment: A period during which the contraction begins slowly.
B-Acme: A period during which the contraction reaches a peak.

C-Decrement: A period during which the contraction diminishes.
- Secondary power: Refers to the power of the-abdominal muscles and
diaphragm, in the form of bearing down effort, which is partly voluntary and

partly involuntary, or reflex.
 Position: Maternal position affects her anatomic and physiologic

adaptations to labor. A woman in labor should be encouraged to find

positions that are most comfortable to her.

 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:

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