INDUCTION OF LABOUR

Definition the artificial initiation of labour to maintain maternal health or to remove the fetus from a potentially harmful environment

Prerequisites For Labour Induction

1. Maternal
   
   • short anterior cervix with open os (ìinducible" or ìripeî)
   • if cervix is not ripe, use prostaglandin (PG) gel (see below)
2. fetal
   
   • adequate fetal monitoring available
   • cephalic presentation
   • good fetal health

Indications

1. Maternal factors
   
   • pregnancy-induced hypertension
   • maternal medical problems, e.g. diabetes, renal or lung disease
2. Maternal-fetal factors
   
   • Rh isoimmunization
   • PROM
   • chorioamnionitis
   • post-term pregnancy
3. Fetal factors
   
   • suspected fetal jeopardy as evidenced by biochemical or biophysical indications
   • fetal demise

Contraindications

1. maternal
   
   • prior classical incision or complete transection of the uterus
   • unstable maternal condition
   • gross CPD
   • active maternal genital herpes
2. maternal-fetal
   
   • placenta or vasa previa
3. fetal
   
   • distress
   • malpresentation

Cervical Ripening Principles

1. PG synthesized by cervical cells and in amniotic fluid to facilitate labour onset and progression
2. PG gel used to augment slow or arrested cervical dilatation or effacement
3. intracervical dinoprostone (Prepidil) when cervix long and closed and no ROM
4. vaginal when cervix favorable, may use with ROM
5. use associated with reduced rate of C/S, instrumental vaginal delivery, and failed induction
6. risks include hyperstimulation and fetal heart rate abnormalities
7. obtain reactive NST prior to administration
8. Foley catheter may be used to mechanically dilate the cervix

Medical

1. oxytocin 2 mU/minute IV, increasing by 1-2 mU/minute every 20-30 minutes to a maximum of 36-48 mU/minute
2. potential complications
3. hyperstimulation/tetanic contraction (may cause fetal distress or rupture of uterus)
4. uterine muscle fatigue, uterine atony (may result in PPH)
5. vasopressin-like action causing anti-diuresis
6. PGF-2 alpha used for intrauterine fetal demise (IUFD)

Surgical

artificial rupture of membranes (amniotomy) - may try this as initial measure

AUGMENTATION OF LABOUR

1. Augmentation of labour is used to promote adequate contractions when spontaneous contractions are inadequate and cervical dilatation or descent of fetus fails to occur
2. Oxytocin @ 2 mU/minute IV, increased by 1-2 mU/minute q 20-30 minutes to a maximum of 36-48 mU/minute
3. Half-life of oxytocin is ~2 minutes (thus need continuous drip because effects wear off fast)