Labor Induction

◈ Labor induction
1. Indication
: Membrane rupture without spontaneous onset of labor
: Maternal hypertension
: Nonreassuring fetal status
: Post-term gestation
* Relative indications
: History of rapid labor and/or Distant residence from the obstetrical facility

2. Contraindication
1) Uterine contraindication : prior disruption (e.g. classical incision or uterine surgery), placenta previa
2) Fetal contraindication : macrosomia, some fetal anomaly (e.g. hydrocephalus, malpresentations)
3) Maternal contraindication : related to maternal size, pelvic anatomy, and selected medical condition (e.g. active genital herpes)

3. Complications
: ↑incidence of chorioamnionitis and cesarean delivery

4. Preinduction cervical ripening
=> Bishop score

* ≥9 : usually successful in the active labor induction
* ≤4 : unfavorable cervix

1) Pharmacological techniques
(1) Prostaglandin E2 (dinoprostone)
: 50%정도 24hr 이내에 active labor 들어감
: indication - Bishop score ≤ 4
: PGE2투여와 oxytocin시작 간의 optimal interval은 정해지지 않았지만, PGE2 투여후 6~12hr이후에 oxytocin 투여하기를 권장
: side effects
- uterine hyperstimulation
; ≥6 contractions in 10 minutes for a total of 20 minutes
: 1% for intracervical gel(0.5mg), 5% for intravagnial gel (2-to 5-mg)
: 보통 투여 후 1hr내에 발생
- fever, vomiting, diarrhea : negligible in low dose

(2) Prostaglandin E1 (misoprostol ; Cytotec)
: vaginal과 oral 투여의 효과는 비슷
- vaginal misoprostol
; 25 ㎍ q 3-6hr
: uterine rupture in women with prior uterine surgery 발생가능(6%)
- oral misoprostol
: 100 ㎍ oral dose = 25㎍ vaginal dose

2) Mechanical techniques
(1) Balloon catheter : infusion of extra-amnionic normal saline
(2) Hygroscopic cervical dilators : laminaria
(3) Membrane stripping
: inserting the index finger as far through the internal os as possible and rotating twice through 360°to separate the membranes from the lower segment
: ⅔가 72hr내에 spontaneous labor에 들어간다.
: ROM, infection, bleeding의 risk는 증가하지 않는다.

※ 각 techniques간에 비교 study는 적고 어떤 방법이든지 benefit은 있다.

5. Labor induction and augmentation
=> Oxytocin
1) Definition
(1) Induction : stimulation of contractions before the spontaneous onset of labor, with or without ruptured membranes
(2) Augmentation : stimulation of spontaneous contraction that are considered inadequate because of failure of progressive dilatation and descent

2) Techniques for IV oxytocin
* Goal : uterine activity that is sufficient to produce cervical change and fetal descent
: avoiding uterine hyperstimulation and/or nonreassuring fetal status
- Contraction >5 in a 10-minute period or 7 in a 15-minute period
=> Continuous contraction monitoring 필요
- Hyperstimulation 발생시, half-life가 5분 이므로 투여 중단하고 지켜보면 된다.
- Dose regimen

- Risks vs Benefits
: uterine rupture - 근래에는 드물지만, uterine surgery를 받았던 경우 발생할 수 있다
: antidiuretic effect - amino-acid homology similar to arginine vasopressin
- water intoxication에 주의

- Uterine contraction pressure
: cervical change없을 때 oxytocin stimulation으로 2시간동안 200 Montevideo unit이상의 contraction 발생시에는 arrest를 진단할 수 있다.

3) Amniotomy (= artificial rupture of the membranes)
=> cord prolapse 주의하고 fetal heart rate monitoring을 하면서 시행하여야 한다.
(1) Elective amniotomy
: AROM with the intention accelerating labor
: 5cm 정도의 cervical dilatation 상태에서 amniotomy를 시행하면 spontaneous labor 1-2시간 단축
(2) Amniotomy induction
: amniotomy alone or combined with oxytocin > oxytocin alone
: early amniotomy가 labor를 더 단축시킬 수 있지만, chorioamnionitis(23%), cord compression(12%)의 발생 가능성이 높다.
(3) Amniotomy augmentation
: induction과 마찬가지로 labor arrest에서 oxytocin과 함께 labor 시간을 단축시키는 효과가 있지만, chorioamnionitis의 위험도가 증가한다.