Every expectant mother hopes to deliver a healthy baby as close as possible to her due date. Normally, labor begins on its own between weeks 37 to 42 of the pregnancy. There are some medical situations, however, in which it is safer to have the baby early than to continue the pregnancy. In these situations, labor is initiated artificially in order to deliver the baby before natural labor begins, usually to reduce health risks to the mother or baby. In other cases, natural labor begins after 37 weeks, but problems arise that put you or your baby at risk. If initiated early or intended to facilitate natural labor, this is referred to as a labor induction.
Labor is defined as the process of uterine contractions and cervical changes that result in the delivery of an infant and the placental. There are three stages:
• First stage: includes early and active labor. During early labor, uterine contractions begin, and the cervix gradually dilates and becomes thinner (effacement). Once the cervix fully dilates to 10 cm, active labor begins, characterized by more intense uterine contractions. This initial stage is the longest part of labor, and can last from 14 to 20 hours.
• Second stage: The infant’s head (or buttocks if breech) passes through the cervix, and enters the vagina during this phase. As the mother pushes, the baby is gradually delivered through the birth canal. This phase typically takes less than three hours, and ends with the birth of the baby.
• Third stage: During this phase, the placenta separates from the inner uterine wall, and is delivered through the vagina. This process may take up to 30 minutes.
You may also want to read our article on How will I know when I’m in labor?
Reasons for Inducing Labor
Currently, over 30 percent of infant births are induced. The reasons for an induction are associated with concerns about the health of the mother or the infant. The most common maternal concerns are high blood pressure (gestational hypertension) and preeclampsia. The latter can result in maternal organ damage or death. Induction may be recommended if the infant seems too small or large for the size of the uterus, or if natural labor does not occur after 42 weeks gestation. In addition to health reasons, labor may be induced at the expectant mother’s request, called an elective induction. Before this is considered, the gestational age and maturity of the fetus must be assessed to determine if an elective induction is safe. Labor induction is often recommended in the following situations:
• Going past your due date: For most women, labor begins by week 40. However, if the infant shows no signs of distress, doctors may wait until the 42nd week (2 weeks after the estimated due date) to declare the pregnancy “overdue,” and medically induce labor. Allowing the pregnancy to continue past 42 weeks increases the risk of a difficult delivery due to the large size of the infant, meconium aspiration, or infant death.
• Nonfunctioning placenta: The placenta carries food and oxygen from the mother’s blood stream to the fetus. After 42 weeks, the placenta may stop functioning, and pose a danger to the health of the fetus.
• Broken bag of waters: In a normal pregnancy, the onset of labor begins when the amniotic fluid sac breaks. If this sac breaks without the onset of labor contractions, induction may be recommended. Allowing the sac to remain open without labor occurring increases the risk of infection. If this sac breaks prior to 37 weeks, it is called a premature rupture of membranes. Because early rupture is often a sign of a problem with the pregnancy, labor induction may be recommended.
• Restart or stimulate labor: If a natural labor slow downs after several hours, artificial stimulation may be used to restart the contractions.
• Health issues of the mother: If the mother has gestational diabetes, hypertension, heart disease, pulmonary disease, an infection or other health issues that might put her or baby at risk, inducing labor can prevent birth complications.
• Placental Problems: If the placenta separates from the uterine wall before labor begins, this deprives the baby of oxygen and nutrients, necessitating an induction.
• Fetal growth: If the fetus is not growing well. This may or may not be associated with insufficient fluid in the amniotic sac.
• Fetal death.
Problems With Being Overdue
There are health problems that can occur past 40 weeks gestation for both the mother and baby. The most dire consequence is death of the fetus.
When a pregnancy goes past the due date, the physician may order tests to assess the health of the baby. These may include a non-stress test, and a fetal ultrasound. The mother may also be asked to monitor the baby’s movements, called “kick counts.” Learn more about kick counts and how to do them.
Criteria for Induction
The following conditions must be met prior to inducing labor:
• The head of the fetus is engaged in the pelvis. Induction is NOT appropriate for breech or transverse positions.
• There was no previous cesarean birth using a classic (midline) uterine incision.
• There is enough room for the baby to pass through the mother’s pelvis.
• No problems with the baby’s heart rate, and the baby is not in distress
• The placenta has begun to separate from the wall of the uterus, but there is no major bleeding
• Placenta previa or vasa previa are not obstructing the cervical opening
• No active genital herpes infection
• Definite signs that natural labor is slowing down
In addition to the above requirements, the hospital staff should be experienced in labor inductions. They should be able to attend to both the mother and baby during the induction process, and have all necessary monitoring equipment. There should also be a doctor available who can perform a cesarean section if necessary.
The following are reasons why labor should not be induced, and are similar to situations where it is unsafe for a mother to have a normal (spontaneous) labor.
• The baby is in a transverse position (lying sideways instead of head or feet down).
• The umbilical cord has dropped down into the vagina instead of the baby.
• The mother had a previous cesarean with a midline incision of the uterus which would be a risk for uterine rupture.
• The mother has a transfundal (top of the uterus) incision from prior surgery (such as fibroid removal).
• The blood vessels of the placenta are in the birth canal before the fetus (vasa previa)
• The placenta has grown over the opening of the cervix (complete placenta previa)
• The mother has an active genital herpes infection which could be transmitted to the baby during delivery.
Labor is seldom induced when the mother is having twins, has had more than 5 pregnancies, or there is excess fluid in the amniotic sac (polyhydramnios).
Medical Ways to Induce Labor
There are a variety of medical ways to induce labor, but we will address the most commonly used techniques. These methods may be used alone or in conjunction with others.
Cervical Ripening Agents
During the first stage of labor, the cervix becomes thinner, and opens to allow the baby to pass through it. It also becomes soft, called “ripening,” in order to stretch during the birth process. The status of the cervix is the most important factor for a successful labor induction. The cervix is considered “ripe” when it becomes soft, effaced more than 50%, and dilated 8 cm or more. When ripening is delayed, there is an increased likelihood of a prolonged labor, reduced oxygen supply to the baby, and the need for a cesarean birth.
A Bishop Score is one way of determining whether an induction will be successful. Scores range from zero to 13, the latter meaning optimal for induction. Each of the five components receives a score of 0-2 or 0-3. The Bishop Score assesses these factors:
• dilation (opening) of the cervix – greater than 5 cm = a score of 3
• consistency of the cervix – a soft cervix dilates easier = a score of 2
• effacement (thinning) of the cervix – greater than 80% = a score of 3
• position of the cervix – anterior or close to the birth canal = a score of 2
• position of the fetus within the pelvis – up to a score of 3
The higher the Bishop Score, the more likely labor induction will be successful. For example a Bishop Score of 8 is similar to that of spontaneous labor, and is favorable for induction. A Bishop Score less than 6 usually indicates that cervical ripening agents will be needed before other labor induction methods are attempted. A mother’s age, weight, height, body mass index, and previous pregnancy history can all influence the success of an induction.
The first step of labor induction is ripening the cervix with a prostaglandin. Misoprostol or Dinoprostone are synthetic prostaglandins that are inserted into the vagina to “ripen the cervix.” After receiving the dose, a mother should remain in a lying down position for up to two hours. A second dose may be administered six hours later if the first dose is ineffective. This method gently induces labor, and increases the efficacy of further induction methods. Dinoprostone may also be used along with oxytocin to induce stronger contractions, or a Foley catheter to dilate the cervix. Depending on the type of prostaglandin used, an oxytocin infusion can be initiated between 30 minutes to 12 hours later.
Side effects of Dinoprostone include:
• Upset stomach
• Flushing of the skin
During a normal active labor, the amniotic sac breaks, and contractions begin or become more intense. An effective way to speed up labor is by breaking amniotic sac (bag of waters that surrounds the baby), called an artificial rupture of membranes. A hook-like instrument is used to puncture the sac, causing the amniotic fluid to run out. As a result, this creates pressure on the cervix which initiates uterine contractions. An amniotomy is a painless procedure, and, in most cases, is effective in starting labor. If labor doesn’t begin or progress as it should after breaking the amniotic sac, IV oxytocin is typically the next step.
Oxytocin is a hormone that is stored in and released by the pituitary gland. It is the primary hormone that stimulates the uterus to contract during labor. It promotes the contractions the help push the baby through the birth canal, and deliver the placenta (or “after birth”). Once the placenta is delivered, oxytocin helps to contract the uterus, and stop the bleeding. Synthetic versions of oxytocin (Pitocin, Syntocinon, or a generic version) are commonly used to induce labor, contract the uterus, and prevent postpartum hemorrhage. They are administered intravenously (IV catheter placed in the arm or hand) to start or strengthen labor contractions. Synthetic oxytocin cannot be take orally because digestive juices in the stomach block its action. It can be used alone, or in combination with an amniotomy, to induce labor. The amount of synthetic oxytocin administered depends on the mother’s ability to accept and tolerate it. The dose is monitored and increased at regular intervals until a stronger contractions occur. When it is no longer needed, the IV infusion can be discontinued. Its effects stop pretty quickly.
Synthetic oxytocin can be administered in a low or high doses. Higher doses make labor and delivery progress quickly. If used with and amniotomy, the amniotic fluid can be assessed for problems with the baby. A fetal heart rate monitor is also used to make sure there is no stress on the baby during the induction. Prior to administering synthetic oxytocin, baselines of the fetal heart rate (FHR), the mother’s vital signs, and uterine activity are measured and recorded. The cervix is checked for effacement and dilation. The presentation and station (how far down in the pelvis the fetus has moved) are also assessed. While receiving the medication, the mother stays in a sitting position, or lies on her left side. The infusion of synthetic oxytocin through an IV begins at a low dose, and is gradually increased until the desired frequency of contractions is attained. For a successful induction, there should be there contractions every 10 minutes, lasting 40-60 seconds each, and one minute between each contraction. A normal contraction pattern during active labor is one every two to three minutes, and lasting about 60 seconds. The oxytocin should also dilate the cervix at a rate of 1 cm per hour during active labor. When the cervix dilates to 5 to 6 cm, the amount of oxytocin can be reduced. The infusion is often stopped after the cervix dilates to 7 to 8 cm. On average, synthetic oxytocin is administered over a 12 to 18 period before it is felt that the induction has failed.
Labor induction is not without risks. Over stimulation of the uterus may harm the baby or mother. If the contractions are too strong, the uterus may rupture. If the contractions occur more frequently than five every 10 minutes, or last more than 90 seconds without a period of rest, this could harm the fetus. It can prevent a good exchange of oxygen and waste through the placenta. During a contraction, blood flow into the uterus is reduced; as the contraction eases up, blood flow resumes and returns to normal flow by the end of the contraction. The infusion of synthetic oxytocin will be stopped if the fetus shows signs of distress on the heart rate monitor. A baseline fetal heart rate should be between 120 and 160 beats per minute (110 to 160 at full term). A higher number indicates fetal distress.
If labor fails to begin or progress within two to three hours, your doctor may opt stop the induction. In this situation, a cesarean delivery is necessary.
Side Effects of oxytocin
For the mother:
• Hypersensitivity to the medicine
• Heart arrhythmia
• Nausea, vomiting
• Rupture of the uterus
For the fetus:
- Slow heart rate (below 120 beats per minute)
- Hypoxia if uterine contractions are too long
- Low Apgar scores after delivery
Risks and Complications of Inducing Labor
For most labor inductions, problems are rare. However, possible complications include:
• Change in the fetal heart rate which indicates fetal distress
• Increased risk of infection in the mother or baby
• Problems with the umbilical cord
• The uterus is overstimulated, and the contractions become too strong or too close together
• The uterus can rupture
Inducing labor also has added risks because:
• An IV tube limits a mother’s mobility which can increase the risk of blood clots
• More frequent monitoring of mother and baby is needed
• More pain relief may be needed due to the intensity of the contractions
• Increased likelihood of a cesarean birth or need for instruments (vacuum or forceps) to help with vaginal birth
To reduce pain, most doctors administer IV pain medication, which can slow down labor, and limit the mother’s mobility.
When Labor Induction Doesn’t Work
Although most women successfully begin labor using one or more of the above methods, there is the chance that the induction will fail. If so, another induction procedure or a cesarian section may be recommended. Depending on your situation, you may need to stay in the hospital for additional monitoring of you and the baby. In other cases, after an amniotomy, you may be allowed to go home. If so, be sure to ask your doctor if any activities should be avoided. and if there is anything in particular to be aware of as your labor begins at home. A failed induction, however, may require a cesarean section to be done right away to prevent problems for you and your baby.
Amniotic Sac: Fluid-filled sac within the mother’s uterus that surrounds the developing fetus.
Cervix: The lower, narrow end of the uterus, near the top of the vagina.
Cesarean Birth: Delivery of a baby through an incision made in the mother’s abdomen and uterus.
Placenta: Tissue that provides nourishment and removes waste from the fetus via the umbilical cord.
Prostaglandins: Chemicals that are made by the body that a variety of effects, including causing the muscle of the uterus to contract, and menstrual cramps.
Uterus: A muscular organ in the female pelvis that contains and nourishes the developing fetus during pregnancy.
Vagina: A passageway surrounded by muscles leading from the uterus to the outside of the body, also known as the birth canal.