Induction of labour Flashcards
What is induction of labour?
Initiation of uterine contractions to accomplish a vaginal delivery before the spontaneous onset of such contractions
Why should labour be induced?
Risks of continuing pregnancy > risks of IOL and delivery
Indications for IOL
- Gestational DM
- Pregnancy-induced HTN/ Pre-eclampsia
- Maternal requests
- Date & time request
- Social support reasons - Advanced maternal age
- Previous poor obstetric history
- IUGR (EFW/AC < 3rd centile)
- Post term pregnancy
- Rupture of membranes
- Twin pregnancy
Timing to deliver in GDM
- Good diet control: Deliver by 41 weeks
- Good control with insulin: Delivery at 37-38 weeks
- Poor control with diet towards end of pregnancy: Delivery at 37-38 weeks
- Poor control with insulin: Aim as close at 37 weeks
Timing to deliver in PIH/pre-eclampsia
37-38 weeks
Timing to deliver in IUGR
?? 37 weeks if dopplers are normal or reduced
Timing to deliver in post-term pregnancy
Post-term pregnancy is > 42 weeks
Timing to deliver in rupture of membranes
- PPROM: aim after 34 weeks (balance with risk of chorioamnionitis)
Timing to deliver in twin pregnancy
Depending on chorionicity, pre-existing maternal/fetal conditions
e.g. MCMA, cord entanglement risk
Timing of delivery for women who are post date
Post date is AFTER EDD (whenever that is)
If at 39 weeks, offer IOL: explain that it reduces the risk of c-sect in low risk woman -> let mommy decide
At 41 weeks, recommend to deliver!!!
When should IOL be avoided?
- Increased risk of uterine rupture
- previous uterine surgery
- previous c-sect
- known connective tissue disorder - Vaginal delivery is contraindicated
- placenta previa
- non-vertex presentations
- severe life threatening maternal/fetal conditions
eg. eclampsia, severe IUGR, acute fetal distress
Ways that labour can be induced
- Mechanical
- Pharmacological
- Surgical
Mechanical methods of IOL
- Membrane sweep (stretch and sweep)
-> stripping attachment of membrane from uterine decidua
~48 hours
- If favourable cervix (according to bishop score) -> better success rate (90%) - Cervical ripening balloon (~24h)
- 2 bulbs and 1 catheter (intrauterine and outside cervix) - Foley’s catheter (~12h)
- Laminaria tent (12-24h)
Mechanical methods - how do they work?
- When membranes are separated from uterine decidua
-> Release of localised prostaglandins F2α, phospholipase A2 & cytokines from the intrauterine tissues
-> Acts on cervical collagen
-> Encourage cervix to soften and stretch
-> Cervical ripening
-> Cause uterine contractions - When there is stretching of the cervix
-> Initiates Ferguson reflex
-> Release of oxytocin
-> Increase uterine activity
Ferguson reflex
- Baby’s head stretches cervix and feedbacks on posterior pituitary
- Pituitary secretes oxytocin into blood and travels to uterine muscle
- Oxytocin stimulates uterine contractions and pushes baby down, stretching the cervix further
- Cycle repeats over and over
Pharmacological (prostaglandins) methods of IOL
- PGE 1 - synthetic analogue (Misoprostol)
- 25mcg
- vaginal tablet insertion every 6h - PGE 2 (dinoprostone - prostin)
- 3mg
- vaginal tablet insertion every 6h - PGE 2 (dinoprostone - cervidil)
- 10mg slow release
- vaginal pessary insertion (24h)
*Half life: 6-12h
*PG F2A (carboprost) cannot be used in IOL as it will cause tonic (sustained) contraction of uterus and hence fetal death
-> given in PPH (uterine atony)
Pharmacological (prostaglandin) methods - how do they work?
Prostaglandins act on cervical collagen
-> Encourage cervix to soften and stretch
-> Cervical ripening
-> Cause uterine contractions
Pharmacological (oxytocin) methods of IOL
Synthetic oxytocin given via IV infusion due to its short half life (3-4min)
- Increased in an incremental fashion to achieve 4 in 10 contractions
- Easily reversible
Pharmacological (oxytocin) methods - how do they work?
There is an increase in myometrial oxytocin receptors as pregnancy progresses (unable to use oxytocin in earlier stages)
-> oxytocin binds to receptor and voltage mediated calcium channels to cause contractions
-> stimulates amnionitic and decidual prostaglandin production
-> mobilises bound intracellular calcium from sarcoplasmic reticulum to activate the myometrial contractile proteins
Uses of oxytocin
- IOL
- Augmentation (already in labour but no progress)
- Active 3rd stage management
- promote uterine involution: oxytocin + ergometrine - Treatment of PPH
- Durotocin - long acting 4-6h contraction
Surgical method - Artificial rupture of membranes (ARM)
Use of an amniotomy hook to break amniotic sac
*done in favourable cervix
Advantages of surgical method - ARM
Reduces duration of labour
Colour of liquor can be assessed
MOA of ARM
Release of natural prostaglandins to commence contractions
Ferguson’s reflex (baby’s head pushing on cervix)
Which method to use for IOL?
Perform vaginal examination:
Use bishop score to assess cervix and baby’s head position
- Score < 6 : unfavourable cervix -> requires cervical ‘ripening’ methods (mechanical VS PGE)
- Score ≥ 6 : favourable cervix -> proceed with artificial rupture of membranes +/- oxytocin
Problems with IOL
- Uterine stimulation
- Increased pain and time & prolonged hospital stay
- Failed IOL (24h)
- Cord prolapse
- Uterine rupture
- Amniotic fluid embolism
Problems with IOL - uterine hyperstimulation
Presence of 5 or more contractions in 10 mins
- Each uterine contraction lasts 45-60s -> during uterine contractions -> no placenta perfusion -> baby relies on own reserves -> needs 90s of uterine relaxation to reperfuse
- 4 contractions in 10 mins is ideal
Can lead to fetal distress, hypoxia
placental abruption, uterine rupture
Management of uterine hyperstimulation
- Remove offending agent: off oxytocin drip
- If cannot, give tocolytic: IV terbutaline to relax uterus
- If cannot, emergency LSCS KIV NVD if possible
Problems with IOL - failed IOL (24h)
- Up to 15%
- Risk factors: AMA, Obesity, early IOL
Management:
- LSCS
- Another cycle or alternative method
Problems with IOL - cord prolapse
Risk factors: ARM with high head (station), multiparity
LSCS
Problems with IOL - uterine rupture
- High fetal mortality rate -> acute loss of placental perfusion
- Risk factors: previous uterine surgery (myomectomy, LSCS, cornual wedge resection), multiparity, connective tissue diseases (Marfan’s syndrome, Ehlers Danlos)
Problems with IOL - amniotic fluid embolism
Very rare, life-threatening condition
Amniotic fluid enters maternal circulation causing multi-organ damage -> 50% mortality rate
Risk factors: oxytocin use, polyhydramnios, multiple pregnancy
IOL in special circumstances
- Previous caesarean section
- Women with a history of 1 previous LSCS can still decide for an IOL if required
- Risk of uterine rupture increases to 2-3% with induction methods, compared to 0.5% with spontaneous labour - Intrauterine fetal demise (IUFD)
- IOL is preferred method of delivery in cases of IUFD at any gestation
- Generally higher doses of prostaglandins can be used as no concern of fetal distress, but attention must be paid to risk of uterine rupture (2-3% risk, VS 0.8% risk with oxytocin + mechanical dilation of cervix)
