ONSET OF LABOR IN ENGLISH

                                             

                                  ONSET OF LABOR IN ENGLISH

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ONSET OF LABOR-

 

Labor-

Series of events that take place in the genital organs in an effort to expel the viable products of  conception (fetus, placenta and the membranes) out of the womb through the vagina into the outer world is called Labor.

Labor (EUTOCIA) is called normal following criteria are fulfilled-

(1) Spontaneous in onset and at term.

(2) With vertex presentation.

(3) Without undue prolongation.

(4) Natural termination with minimal aids.

(5) Without having any complications affecting the       health of the mother and/or the baby.

 

Cause of onset of labor

There is no clarity about what causes onset of labor still some theories are-

Uterine distension: Stretching effect on the myometrium by the growing fetus and liquor amnii can explain the onset of labor at least in twins or poly-hydramnios.

Uterine stretch increases gap junction proteins, receptors for oxytocin and specific contraction associated proteins (CAPs).

Feto-placental contribution: fetal hypothalamic-pituitary- adrenal axis-  Just before onset of labor there is increased CRH  in fetal hypothalamus→ increased release of ACTH from fetal pituitary and→ increased cortisol secretion from fetal adrenals → accelerated. This event leads to production of estrogen and prostaglandins from the placenta

This estrogen — Increases the release of oxytocin from maternal pituitary. — Promotes the synthesis of myometrial receptors for oxytocin, prostaglandins and increase in gap junctions in myometrial cells.

— Accelerates lysosomal disintegration in the decidual and amnion cells resulting in increased prostaglandin (PGF2α) synthesis. — Stimulates the synthesis of myometrial contractile protein—actomyosin 

  and  Increases the excitability of the myometrial cell membranes.

Progesterone:   Progesterone levels  fall before labor (due to fetal cortisol and de-hydro-epi-androsterone sulfate (DHEA-S) . Change in the estrogen : progesterone ratio rather is linked with prostaglandin synthesis.

Prostaglandins: Prostaglandins are the important factors, which initiate and maintain labor.

 

Pre Labor Stage-

PRELABOR: (premonitory stage): The premonitory stage may begin 2–3 weeks before the onset of true labor in primigravidae and a few days before in multiparae. The features are inconsistent

and may consist of the following:

•        Lightening

•        Cervical changes

•        Appearance of false labor pain

 

Lightening-

A few weeks prior to the onset of labor especially in primigravidae, the presenting part sinks into the true pelvis. It is due to active pulling up of the lower pole of the uterus around the presenting part. 

This diminishes the fundal height and hence minimizes the pressure on the diaphragm. It is a  welcome sign as it rules out cephalopelvic disproportion and other conditions preventing the head from entering the pelvic inlet.

Cervical changes-

Cervical changes: A few days prior to the onset of labor, cervix becomes ripe. A ripe cervix is

(a)    soft,

(b)    80% effaced (<1.5 cm in length),

(c) Admits one finger easily, and

(d) Cervical canal is dilatable.

Appearance of False labor pain-

False labor pain is –

      (i)          Dull in nature,

(ii) confined to lower abdomen and groin,

(iii) not associated with hardening of the uterus,

(iv) they have no other features of true labor  pain 

(v) usually relieved by enema or sedative.

 

Identifying the onset of labor-

The onset of labor is a process and is very difficult to identify exactly when the painless (sometimes painful) contractions of pre-labour develop into the progressive rhythmic contractions of actual labour. Onset of labor is assumed to start when rhythmic pattern of contraction starts and results in effacement and dilatation

True labor pain is : (i) Painful uterine contractions at regular intervals, (ii) frequency of contractions increase gradually, (iii) intensity and duration of contractions increase progressively, (iv) associated with “show”, (v) progressive effacement and  dilatation of the cervix, (vi) descent of the presenting part, (vii) formation of the “bag of forewaters” and (viii) not relieved by enema or sedatives.

Show: With the onset of labor, there is profuse cervical secretion. Simultaneously, there is slight oozing of blood from rupture of capillary vessels of the cervix and from the raw decidual surface caused by separation of the membranes due to stretching of the lower uterine segment. Expulsion of cervical mucus plug mixed with blood is called “show”.

Formation of bag of waters- Due to stretching of the lower uterine segment and With the dilatation of the cervical canal, the lower pole of the fetal membranes becomes unsupported and tends to bulge into the cervical canal. As it contains liquor, which has passed below the presenting part, it is called “bag of waters”.