Physiology of prelabour period & labour

Indications for induction of labour

How to assess if induction of labour is going to end with successful vaginal delivery?

How to induce labour?

Complications of induction of labour

Induction of labour it is the process whereby labor is initiated by artificial means.Augmentation of labor is an artificial stimulation of labor that had already begun spontaneously.

Before taking the decision of termination of pregnancy by induction of labor we have to consider the following factors:

The risk if pregnancy is interrupted ,i.e fetal maturity & complications of the induction process.

The risk if pregnancy is continued whether fetal

or maternal

To carry on the process of labor we have to understand the physiology of spontaneous labor that the human labor is not a sudden event but rather a culmination of a gradual process which evolve over a period of several weeks (pre labor period).

the critical events during pre labor period (that is 4-5 weeks prior to labor) are:

1.Increase in myometrial contractility gradually.

during pregnancy there is Brakston Hichs contractions then at 35 weeks those contractions become regular, stronger & more frequent & built up during the last 4-5 weeks of gestation & ended by labor contractions.

2.Cervical ripening :changes in cervix during pre labor & labor period.

those changes regarding shape & consistency of cervix& these include:

Decrease in collagen content from80% to 50% Increase intervening space between microfibril Increase in ground substance which is filled

with polysaccharides Decrease in hydroxyprolin content.All those changes are responsible for softening &

increase compliance of cervix which make it ready for stretching & dilatation with effacement that occur in response to uterine contractions.

Spontaneous laborTheories behind the start of labor are:1.Change in progesteron/estrogen that

prog. decreased & est. increased which decrease the ratio & this will increase PG syntheses.

2.During late pregnancy there is increase in syntheses of PG (E2 & F2 α )which are synthesized in the desidua & the amnion . There may be a signal from trophoblast or the fetus that decrease the inhibitors for PG syntheses that present in the amniotic fluid .

The main function of PG : Cervical ripening. Increase myometrial contractility. Increase sensitivity of myometrium to the

exogenous oxytocin.3.Prior to the onset of labor there is a very

slight increase in oxytocin con. which could be a facilitating mechanism during labor.

4.The fetal hypothalamic – pituitary –adrenal axis could be responsible for triggering the onset of labor by corticosteroid & oxytocin from fetal pituitary.

Indications of induction of labor

The objectives of induction of labor is to produce a labor that is closely similar to spontaneous labor without subjecting the mother or fetus to any risks & to achieve vaginal delivery of a neonate that is intact physically & mentally by a mother who were left without any damage physically & mentally.

Maternal indications Pre eclapsia or hypertension DM sometimes. Sometimes in patient with heart diseases.

Feto placental Prolong pregnancy IUGR & IUD. Impairment of fetal wellbeing proved by

various tests. Rh incompatibility. Fetal congenital malformation. Chorio amnionitis PROM,APH .

Contra indications for induction of labor & augmentation

Contracted pelvis . Previous C.S. Complete transectio of uterine wall during

myomectomy or metroplasty. Overdistention of uterus. Pretem fetus without lung maturity Acut fetal distress. Malpresentations (breech, brow,

transverse lie, oblique lie)

The indications for augmentation of labor Abnormality of any phase or stage of labor due

to Inefficient uterine c contraction.

The main factor affecting successfulness of induction of labour is

State of cervix a ripped cervix make induction of labor

easier & successful& the best method to assess the prognosis of labor is by Bishope score

>=5 3-4 1-2 0 Dilatation of cervix (cm)

Soft Medium Firm Consistency of cervix

<0.5 1-0.5 2-1 <2 Length of cervical canal (cm)

Anterior Central Posterior Position of cervix

below 1or 0 2 3 Station (cm above ischial spines)

0 1 2 3

Cervical favourability

High score indicate cervical rippening score of 8 & more indicate that interval

to labor only 3 days score of less than 2 indicate that

interval to labor could be more than 3 weeks.

low score can be improved by PG that increase cervical rippening

Methods for induction of labor1.Amniotomy & oxytocin infusion this can give the best results rather if one

of the 2 methods is used alone oxytocin is given by i.v infusion pump&

the starting dose is 1mu/min. , then the dose is doubled every 15 -20 min. according to uterine contraction.

the sensitivity of individual patient vary widely.

oxytocin infusion is less effective prior to amniotomy so if amniotomy don after oxytocin infusion there may be increase in uterine contraction & the dose of oxytocin should be adjusted.

2.PG;: oral tab 0.5 mg of PG E2 following

amniotomy the dose repeated per hour Vaginal PG as( prostin vaginal tab )of 3mg

PG E2 every 6 hours till labor is established or application of jelly to the cervix

Extra amniotic infusion of PG by Folleys catheter

i.v. rout for PG is not used because it is

associated with a lot of side effects as hypotension , nausea & vomiting.

Complications of induction of labor1. Excessive uterine contraction & rupture

of uterus.2. Fetal distress.3. Oxytocin has anti diuretic effect & large

doses may lead to water intoxication.4. Prolonged period of oxytocin use &

uterine contraction may lead to exhaustion of myometrium & PPH.

5. Neonatal jaundice .