Labor induction refers to any of a number of methods for artificially stimulating childbirth.
Commonly accepted medical reasons for induction include:
- Postterm pregnancy, i.e. if the pregnancy has gone past the 41st week.
- Intrauterine fetal growth retardation (IUGR).
- There are health risks to the woman in continuing the pregnancy (e.g. she has pre-eclampsia).
- Premature rupture of the membranes (PROM); this is when the membranes have ruptured, but labor does not start within a specific amount of time.
- Premature termination of the pregnancy (abortion).
- Fetal death in utero.
- Twin pregnancy continuing beyond 38 weeks.
Methods of induction
Methods of inducing labor include both pharmacological medication and mechanical or physical approaches.
Mechanical and physical approaches can include artificial rupture of membranes or membrane sweeping. The use of intrauterine catheters are also indicated. These work by compressing the cervix mechanically to generate release on prostaglandins in local tissues. There is no direct effect on the uterus.
Pharmacological methods are mainly using either dinoprostone (prostaglandin E2) or misoprostol (a prostaglandin E1 analogue)
- Intravaginal, endocervical or extra-amniotic administration of prostaglandin, such as dinoprostone or misoprostol. Prostaglandin E2 is the most studied compound and with most evidence behind it. A range of different dosage forms are available with a variety of routes possible. The use of misoprostol has been extensively studied but normally in small, poorly defined studies. Only a very few countries have approved misoprostol for use in induction of labour.
- Intravenous administration of synthetic oxytocin preparations, such as Pitocin.
- Use of mifepristone has been described but is rarely used in practice.
- Relaxin has been investigated, but is not currently commonly used.
Mechanical and physical approaches
- "Membrane sweep", also known as membrane stripping, or "stretch and sweep" in Australia and the UK – during an internal examination, the practitioner moves her finger around the cervix to stimulate and/or separate the membranes around the baby from the cervix. This causes a release of prostaglandins which can help to kick-start labor.
- Artificial rupture of the membranes (AROM or ARM) ("breaking the waters")
- Extra-amniotic saline infusion (EASI), in which a Foley catheter is inserted into the cervix and the distal portion expanded to dilate it and to release prostaglandins.
When to induce
For the health of the mother and baby labor should begin without induction when the cervix is unfavorable prior to 41 weeks.
Observational/retrospective studies have shown that non-indicated, elective inductions before the 41st week of gestation are associated with an increased risk of requiring a caesarean section. However, randomized clinical trials have not been used to study this question. Doctors and patients should have a discussion of risks and benefits when considering an induction of labor in the absence of an accepted medical indiction.
Until recently, the most common practice has been to induce labor by the end of the 42nd week of gestation. This practice is still very common. In the UK, a dating scan is usually conducted around the 12th week of pregnancy to determine the estimated due date. Research suggests that scans done after this date can cause the estimated due date to become less accurate, with the longer time that passes. In the cases of late dating scans, the estimated due date is less accurate which could therefore provoke a woman to be induced unnecessarily. Studies have shown a slight increase in risk of infant mortality for births in the 41st and particularly 42nd week of gestation, as well as a higher risk of injury to the mother and child. Due to the increasing risks of advanced gestation, induction appears to reduce the risk for cesarean delivery after 41 weeks gestation.
Inducing labor before 39 weeks increases the risk of complications of prematurity including difficulties with respiration, infection, feeding, jaundice, neonatal intensive care unit admissions, and perinatal death.
The odds of having a vaginal delivery after labor induction are assessed by a "Bishop Score". A Bishop Score is done to assess the progression of the cervix prior to an induction. In order to do this, the cervix must be checked to see how much it has effaced, thinned out, and how far dilated it is. The score goes by a points system depending on five factors. Each factor is scored on a scale of either 0-2 or 0–3, any score that adds up to be less than 5 holds a higher risk of delivering by cesarean section.
Criticisms of induction
Induced labor may be more painful for the woman. This can lead to the increased use of analgesics and other pain-relieving pharmaceuticals. These interventions have been said to lead to an increased likelihood of caesarean section delivery for the baby. However, studies into this matter show differing results. One study indicated that while overall caesarean section rates from 1990–1997 remained at or below 20%, elective induction was associated with a doubling of the rate of caesarean section . Two more recent studies have shown that induction may increase the risk of caesarean section if performed before the 40th week of gestation, but it has no effect or actually lowers the risk if performed after the 40th week. Elective induction in women who were not post-term increased a woman's chance of a C-section by two to three times.
The most recent review on the subject of induction and its effect on Cesaerean section indicate that there is no increase with induction and in fact there can be a reduction.
- Tocolytics, labor repressants
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