Labor induction: indications, contra indications, methods predicting success of labor induction, complications of labor induction.

Indications of labor induction :

The indications for labor induction can be subdivided into maternal , fetal or social or a combination of these.

A. Maternal indications:

1. Obstetrical indications:

 Post dated or post term pregnancy        

 Ante partum hemorrhage

 Red-cell alloimmunisation

 Previous unexplained still birth at term

 Intrauterine fetal death

 Oligohydromnios

Congenital fetal malformations

 Premature rupture of membranes

2. Medical indications:

 Chronic nephritis superimposed acute nephritis and failure

 Hypertension

 Diabetes

B. Fetal indications:

 Placental insuffiency

 IUGR

 Postdatism

Rh isoimmunisation

Previous unexplained still births

Deteriorating antenatal tests for fetal wellbeing.

Specific definitions and the relative importance of the various indications for labor induction vary between obstetrician, obstetric unit and country.

Post dated pregnancy is probably the commonest indication in many units but definitions may include any gestation beyond 40, 41 or 42 completed weeks of gestation.

Some obstetricians consider that cervical state should determine the timing of delivery,  particularly when post–dates pregnancy is the indication for induction. It must be remembered however , that there is often a poor relationship between cervical favorability and gestational age.

Hypertensive states constitute the second most common primary indication for labor induction in many obstetric units, again generally because of anticipated fetal or maternal problems rather than because of evidence of deteriorating maternal or fetal health.

The other indications are varied, some universally accepted, such as recent or current ante partum hemorrhage, diabetes mellitus, red cell alloimmunisation, demonstrable placental failure and previous unexplained still birth at term and others with little logic, such as fetal breech presentation and suspected cephalo- pelvic disproportion. In many countries there is now a reluctance to encourage labor when there is a fetal breech presentation.

Labor induction performed at maternal request or convenience at term is generally frowned upon. However the reluctance to accommodate such requests, believing it is not in the best interests of mother or fetus, is at variance with the willingness to allow patients to opt  for delivery by elective cesarean section, usually performed before full term, particularly in cases such as breech presentation or previous delivery by caesarean section.

                                                                                                                             

Contraindications to labor induction:

A. Absolute:

1. Disproportion that is more than borderline.

2. Where the lie is other than longitudinal, for obvious reasons.    

3. In cases of previous caesarean section for contracted pelvis or who have failed in a previous trail of labor for disproportion.

4. Where a tumor occupies the pelvis.

5. When vaginal delivery is contraindicated in conditions like major degree placentaprevia, vasaprevia, cord presentation and prolapse, invasive carcinoma of cervix and infections like active herpes genitalis.

6. Previous classical caesarean section.

7. Regular contractions.

8. Unification surgery for uterine didelphis.

B. Relative contraindications:

1. Maternal heart disease

2. Breech presentation

3. Multiple pregnancy

4. Poor biophysical profile and Doppler studies

5. Grand multipara

6. Previous myomectomy

7. A history of prior difficult or traumatic delivery   

8. Maternal fever

Predicting the success of labor induction:

Cervical condition exerts a significant influence upon induced labor outcome and its consequences. The decision about how to induce labor must take account of the favorability of cervix.

To assist an obstetrician in deciding which way to induce labor a cervical scoring system is often used. More than 12 different pelvic or cervical scoring schemes have been described during the past 70 yrs, but only four to five are in vogue.

The semi-quantitative clinical scoring system described by Bishop in 1964 is the one most widely employed.  He originally described it with basic requirements of multiparity, gestational age >36 weeks, vertex presentation, normal previous and present obstetric history, advance knowledge and permission of the patient.  The score uses the cervical dilatation, effacement, consistency, position, and the station of the presenting part.

Because it is simple and has the most predictive value , it was used in many studies and doctoral dissertations   to assess the predictability of induction and to determine the agent to be used.       

                                                                                                                                                                   Bishop score :

parameter	0	1	2	3
position	posterior	intermediate	anterior	-
consistency	firm	intermediate	soft	-
effacement	0 to 30%	40 to 50%	60 to 70%	≥80%
dilatation	<1cm	1 to 2 cms	2 to 4cms	> 4 cms
Foetalstation	- 3	- 2	- 1, 0	+ 1 to + 2

Bishop score is somewhat subjective, but a score of less than 5 suggests further ripening is needed, while a score of 9 or greater suggests that ripening is completed.

The modified Bishop score by Calder:

Calder modified the original Bishop score in 1974, which is known as the modified Bishop score and is currently used by most obstetric units.^. He replaced the ‘effacement of cervix’ denoted as percentage in the original score with length of cervix in centimeters, which is having more reproducibility and reliability than original Bishop score.

Modified bishop score:

parameter	0	1	2	3
position	posterior	intermediate	anterior	-
consistency	firm	intermediate	soft	-
Length of cx	>3cms	>2cms	>1cm	> 0cm
dilatation	<1cm	1 to 2 cms	2 to 4cms	> 4 cms
Foetalstation	- 3	- 2	- 1, 0	+ 1 to + 2

Maximum possible score would be 12, at which point , of course delivery would be just about imminent.

As the evaluation of score rises, the latent phase becomes shorter. This is an important matter because the latent phase contributes significantly to a   prolonged induction to delivery interval. Of all the parameters of the score , the degree of cervical dilatation seems to be the most important .However once the active phase of labor supervenes it does not necessarily differ significantly in length or other characteristics from spontaneous labor.

Other cervical scoring systems that were described in literature were as follows :

 Calkins  in 1930 :  

First published description of a method to quantify cervical factors that could predict the course of labour.

Multiparity was taken as predictive of successful labor.

Dichotomous scoring system

effacement :  present / absent

engagement:  above/ below spines

consistency:  soft -like lips=2/ firm like nose=3

Labor intensity:   good =  one contraction/3min, 

                                fair=one contraction/5min,

                                 poor=one contraction/>5min

If completely favourable, in 95-100% of women had 1^st stag of less than 6 hrs. Assessment was made via rectal examination.

 Cocks in 1955 :

 having 5 categories of cervix                                                                           

1.      Soft, effaced ,1cm dilated

2.      Soft,uneffaced,1cm dilated

3.      Firm,somewhat effaced,closed os

4.      Firm, uneffaced,closed os

5.      Anomalous cervix

Modified Bishop score by Friedman  in 1967:

Multiply Bishop factor

Factor	Simple weighting	complete weighting
Dilatation	2	4
Effacement	1	2
Station	1	2
Consistency	1	2
Position	0	1
Range of scores	0-14	0-30

Ultrasound assessment of the cervix has been investigated as a way of predicting the likely outcome of induced labour as an alternative to clinical digital examination.

Before proceeding to trans vaginal ultrasound the woman was asked to empty the bladder.

The endo vaginal probe is first covered with a sterile condom into which has been placed sterile gel. The condom prevents vaginal secretions from contacting the probe. Sterile gel is also applied to the outside of the condom.

As described by Anderson  with the patient in lithotomic position, 5 Mhz vaginal probe was introduced into the vagina and the length and width of the cervix was measured with the probe placed in the anterior fornix of the vagina. The appropriate sagital view of the cervix was obtained by simultaneous imaging of external and internal os.

External os was identified by its triangular echo density and internal os by its v shape appearance. The cervical canal was seen as a triangular line connecting these two points. The distance between the external and internal os taken as cervical length. The width was measured at the level of internal os. All these measurements were repeated thrice and the average of the readings was taken for statistical analysis.

To reduce inter observer variability and improve reproducibility of cervical measurements using trans vaginal ultrasonography , the following criteria were adopted.

The internal os is visualized as a flat dimple or an isosceles triangle

The whole length of cervix is visualized

The external os appears symmetric

The distance from the surface of the posterior lip to the cervical canal is equal to the distance from the surface of the anterior lip to the cervical canal.

Transducer pressure on the cervix is kept to minimum.

The widest viewing angle of the available ultrasound field should be used.

Ultrasonographic cervical measurement has been known as a reproducible , objective and quantitative method and can be performed easily.

Cervical length of > 2.8 cm was shown to have a better sensitivity in deciding the need for cervical ripening.

If there is no much change in cervical length 6 hrs after induction it can predict the prolongation of induction.

 Parity is another factor which may predict the success of labor induction. parity  is an independent predictor of the total duration of labor as well as the duration of induction.

For the same cervical length, the induction to delivery interval in multigravidae was 37 % lower than nulligravidae. The incidence of successful vaginal delivery within 24 hrs of induction was about 30% higher than in nulligravidae.

Other factors in predicting the success of labor:

Fetal fibronectin (FFN) concentration in cervical transudate represent a laboratory approach and have been shown to correlate with induced labor outcome with concentrations greater than 50 microgs/ml associated with a favorable cervix and reduced intrapartum morbidity.

Electrical impedance measurements across the surface of the cervix using a 8 mm tetrapolar pencil probe have been used to investigate correlations with clinical examination to assess cervical favorability.

Serum nitrite/ nitrate levels have also been assayed in nulliparae  undergoing prostaglandin induction of labor and using multiple regression analyses significantly lower levels of each were found in women who delivering over a longer period.

Labour induction is not without its risks for the mother and particularly for the fetus

Complications :

 1. Inadvertent delivery of a preterm baby has largely been eliminated by the widespread use of ultrasound assessment of gestation.

2. Unforeseen cephalo pelvic disproportion

3. Sepsis, risk is negligible, if amniotic sac is intact. Risk increases if  membranes have been ruptured.

4. Partial placental detachment in cases of surgical induction if placenta sited low in uterus. And bloody tap in cases of vasa preavia.

5. Accidental hemorrhage, abruptioplacenta in cases of polyhydromnios following ARM due to sudden release of enormous quantities of liquor.

6.  Fetal pneumonia due to prolonged retention of the fetus in utero with ruptured membranes, particularly in association with prolonged labor.

7. Cord prolapse, when amniotomy done and fails to engage or in malpresentation

8. Amniotic fluid embolism

9. Prolonged oxytocin infusion can lead to fluid and electrolyte imbalance to mother and in baby neonatal jaundice can occur due to osmotic fragility of erythrocytes.

10. Uterine hyper stimulation                                                                                                                   

11. Failed attempts at induction leading to caesarean section probably because of mistaken belief that any attempt at inducing labor should not persist beyond a few hours.

12. Any possible long term consequences for the babies

The issue of cost benefit equations is now an important factor to be taken into account, when discussing alternate options. Thus not only must the method of labor induction be safe and acceptable for the mother and fetus, it must also be cost effective.

The search for an ideal method of induction that modulates the unfavorable cervix to favorable cervix without stimulating uterine contractions and improves the ultimate outcome of labor, almost eliminates the risk to fetus still has to be found.