Induction of labour

What it is

Induction of labour brings on labour instead of letting it begin on its own. The indications are prolonged pregnancy at 41-42 weeks, maternal or pregnancy disease such as DM, HTN, preeclampsia, renal disease or antiphospholipid syndrome, term PROM and PPROM at 34-36 weeks, chorioamnionitis, fetal compromise or fetal demise, significant but stable antepartum hemorrhage, and IUGR. After term PROM the rule is to wait 24 hours for spontaneous vaginal delivery, then induce. In a woman at 41 weeks the next step is induction, with an appointment given at 42 weeks gestation. In GDM the timing is set by the treatment: on diet, 40 weeks; on metformin and well controlled, 39 weeks; on insulin and well controlled, 38 weeks; on metformin or insulin and uncontrolled, 37-38 weeks. Reduced fetal movement at term means induced at any time, anomalies with good control means induced at term, and with macrosomia it depends on the time of presentation.

How it is diagnosed

The cervix is assessed before anything is started. The Bishop score is made of five physical findings, and each has its own points:

1. Cervix position: posterior 0, central 1, anterior 2.
2. Consistency: firm 0, medium 1, soft 2.
3. Effacement %: 0-30 is 0, 40-50 is 1, 60-70 is 2, 80 or more is 3.
4. Dilatation: 0 is 0, 1-2 is 1, 3-4 is 2, 5 or more is 3.
5. Fetal head station: -3 is 0, -2 is 1, -1 is 2, +1 is 3.

So the maximum is 13, and under 6 the cervix is not favorable for a vaginal birth. The higher the total the more favorable the cervix, with 9 or more associated with 100% successful inductions in the clinical trial. A modified Bishop scoring system is also given, and it runs 0 to 2 only, over five factors: dilatation 0, 1-2, 3-4 cm; length >3, 1-3, <1 cm; consistency firm, medium, soft; position posterior, mid, anterior; and station -3 or above, -2, -1 to 0. The two scales differ. The SQUH protocol is written to the modified one: favorability, or ripeness, of the cervix is the most important predictor of success and is assessed by determining the modified Bishop Score, and the cervix is unfavorable when the score is estimated at less than 6.