normal labour

 DEFINITION: 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.

-It may occur prior to 37 completed weeks, when it is called the preterm labor.

-Labor is characterized by the presence of regular uterine contractions with effacement and dilatation of the cervix and fetal descent.

-Delivery is the expulsion or extraction of a viable fetus out of the womb.

It is not synonymous with labor; delivery can take place without labor as in elective cesarean section.

Delivery may be vaginal, either spontaneous or aided, or it may be abdominal.

NORMAL LABOR (EUTOCIA): Labor is called normal if it fulfills the following criteria.

 (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.

ABNORMAL LABOR (DYSTOCIA): Any deviation from the definition of normal labor is called

Abnormal labor. Thus, labor in a case with presentation other than vertex or having some complications

even with vertex presentation affecting the course of labor or modifying the nature of termination or

adversely affecting the maternal and/or fetal prognosis is called abnormal labor.

DATE OF ONSET OF LABOR

Based on the formula, labor starts approximately 

on the expected date in 4%,

 1 week on either side in 50%,

 2 weeks earlier

  1 week later in 80%, 

at 42 weeks in 10%, 

 at 43 weeks plus in 4%.

CAUSES OF ONSET OF LABOR

 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 polyhydramnios. Uterine stretch increases gap junction

proteins, receptors for oxytocin and specific contraction associated proteins (CAPs).

 Fetoplacental contribution: Cascade of events activate fetal hypothalamic-pituitary-adrenal axis

prior to onset of labor → increased CRH → increased release of ACTH → fetal adrenals → increased cortisol secretion → accelerated production of estrogen and prostaglandins from the placenta

 Estrogen: The probable mechanisms are:

— Increases the release of oxytocin from maternal pituitary.

— Promotes the synthesis of myometrial receptors for oxytocin (by 100–200 folds), 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 through cAMP.

— Increases the excitability of the myometrial cell membranes.

 Progesterone: Increased fetal production of dehydroepiandrosterone sulfate (DHEA-S) and cortisol

inhibits the conversion of fetal pregnenolone to progesterone. Progesterone levels therefore fall

before labor. It is the alteration in the estrogen : progesterone ratio rather than the fall in the

absolute concentration of progesterone, which is linked with prostaglandin synthesis.

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

major sites of synthesis of prostaglandins are—amnion, chorion, decidual cells and myometrium.

Synthesis is triggered by—rise in estrogen level, glucocorticoids, mechanical stretching in late

pregnancy, increase in cytokines (IL–1, 6, TNF), infection, vaginal examination, and separation or

rupture of the membranes. Prostaglandins enhance gap junction (intermembranous gap between

two cells through which stimulus flows) formation.

FALSE PAIN: (Synonym: false labor, spurious labor):

 It is found more in primigravidae than in parous women. 

It usually appears prior to the onset of true labor pain by 1 or 2 weeks in primigravidae and

by a few days in multiparae. Such pains are probably due to stretching of the cervix and lower uterine

segment with consequent irritation of the neighboring ganglia.

PRELABOR: (Synonym: 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”: 

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. It signifies incorporation of the lower uterine segment into the wall of the uterus.

This diminishes the fundal height and hence minimizes the pressure on the diaphragm (Fig. 13.2).

The mother experiences a sense of relief from the mechanical cardiorespiratory embarrassment.

There may be frequency of micturition or constipation due to mechanical factor—pressure by

the engaged presenting part. It is a welcome sign as it rules out cephalopelvic disproportion and

other conditions preventing the head from entering the pelvic inlet.

 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.

True labor pain is characterized by: 

(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” 

 (viii) not relieved by enema or sedatives.

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 as discussed above and

(v) usually relieved by enema or sedative.

Labor pain: Throughout pregnancy, painless Braxton Hicks contractions with simultaneous

hardening of the uterus occur. These contractions change their character, become more powerful,

intermittent and are associated with pain. Pain more often felt in front of the abdomen or

radiating toward the thighs.

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”.

Dilatation of internal os: With the onset of labor pain, the cervical canal begins to dilate more in the upper part than in the lower, the former being accompanied by corresponding stretching

of the lower uterine segment.

Formation of “bag of waters”: Due to stretching of the lower uterine segment, the membranes are detached easily because of its loose attachment to the poorly formed decidua. 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”. During uterine contraction with consequent rise of intra-amniotic

pressure, this bag becomes tense and convex. After the contractions pass off, the bulging may

disappear completely. This is almost a certain sign of onset of labor. However, in some cases

the membranes are so well applied to the head that the finding may not be detected.

STAGES OF LABOR: Conventionally, events of labor are divided into three stages:

 First stage: It starts from the onset of true labor pain and ends with full dilatation of the cervix. It

is, in other words, the “cervical stage” of labor. Its average duration is 12 hours in primigravidae

and 6 hours in multiparae.

 Second stage: It starts from the full dilatation of the cervix (not from the rupture of the membranes)

and ends with expulsion of the fetus from the birth canal. It has got two phases—(1) The propulsive

phase—starts from full dilatation up to the descent of the presenting part to the pelvic floor.

(2) The expulsive phase is distinguished by maternal bearing down efforts and ends with delivery

of the baby. Its average duration is 2 hours in primigravidae and 30 minutes in multiparae.

 Third stage: It begins after expulsion of the fetus and ends with expulsion of the placenta and

membranes (afterbirths). Its average duration is about 15 minutes in both primigravidae and

multiparae. The duration is, however, reduced to 5 minutes in active management.

 Fourth stage: It is the stage of observation for at least 1 hour after expulsion of the afterbirths.

During this period maternal vitals, uterine retraction and any vaginal bleeding are monitored.

Baby is examined. These are done to ensure that both the mother and baby are well.