Normal labour-Causes and Physiology

Although prostaglandins were originally isolated from prostate glands, seminal vesicles, and semen,

their synthesis in other organs has been amply documented; indeed, few organs have failed to demonstrate prostaglandin release. Prostaglandins cause platelet aggregation, smooth-muscle contraction, vasodilation, and uterine contraction. Prostaglandins are synthesized from arachidonic acid, a 20-carbon fatty acid with interspersed carbon double bonds. Signals such as angiotensin II, bradykinin, epinephrine, and thrombin can activate phospholipase A2 and release arachidonic acid from membrane lipids. The arachidonic acid is cyclized by cyclooxygenase to form prostaglandins. Arachidonic acid can also be oxidized to leukotrienes by the action of lipoxygenases.

Occur during most of the months of pregnancy

Ans. is b i.e. Short vagina.

Differences between true and false labour pains.

Mtures

Cervical changes (dilatation & effacement) Frequency & duration of contractions Pain

Bag of water

Show

Relief with enema / sedation

True labour pains Present

Regular & gradually T

Lower abdomen & back, radiating to thighs

Formed Present No

False labour pains Absent

Irregular

Lower abdomen only

Not formed Absent

Yes

30 mm Hg

Beginning of labour

Decreases

Absence of ‘bag of water’

Ans. is a i.e. Montevideo units

Montevideo unit is to define uterine activity.

According to it, uterine performance is the product of the intensity – (increased uterine pressure above baseline tone of a contraction) in mm of Hg multiplied by contraction frequency per 10 minutes. For example 3 contrac­tions in 10 minutes, each of 50 mm of Hg intensity would be equal to 150 Montevideo units.

As per this:

Clinical labour usually commences when uterine activity reaches values between 80-120 Montevideo units. (This translates into approximate 3 contractions of 40 mm of Hg every 10 minutes)

During labour – Normal uterine contractions are between 190 – 300 Montevideo units (At the time of delivery it is 300 Montevideo units)

Extra Edge

• Uerine contractions are clinically palpable only after their intensity exceeds > 10 mm of Hg

Uterine contractions are not associated with pain unless their intensity is > 15 mm of Hg.

Formation of bag of waters is almost a certain sign of onset of labour. During dilatation of the cervical membrane the unsupported lower pole of the fetal membranes tends to bulge into the cervical canal. It is called bag of waters when this bulging membrane contains amniotic fluid. When uterine contractions occur this bag becomes tense and convex, and it disappears when the contraction passes off.

Features of true labour pains:

• Occurrence of painful uterine contractions at regular intervals
• Contraction with increasing intensity and duration
• Show
• Progressive effacement and dilatation of cervix
• Formation of bag of waters

Ref: Textbook of Obstetrics By D.C Dutta, 6th edn, page 117.

PGE₂

Ans. C i.e. 10 cm

Ans. B: Show

Features of true pain:

• Painful uterine contractions at regular intervals
• Contraction with increasing intensity and duration
• Expulsion of cervical mucus plug, mixed with blood (show)
• Progressive effacement and dilatation of cervix
• Formation of bag of waters

The organ shown in the picture above represents uterus.

Pressure inside the uterus in early stage of labor is about 50  mm Hg.