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”.
