Indications

Prevention of maternal disease

Although induction of labour is generally either indicated on behalf of the mother or on behalf of the fetus, in many cases the two overlap and induction is mutually beneficial.

Maternal disease can either be pregestational or gestational; how­ever, the same physiological processes generally mediate the risk to continuation of the pregnancy. Hypertension and diabetes fall along a continuum of maternal vascular disease that has the potential to compromise placentation and thus puts a pregnancy at risk of pla­cental insufficiency as gestational age increases. There are slightly different points at which outcomes are seen to worsen when preg­nancies go undelivered depending upon the specific pathology and its severity. Pregnancies affected by either uncomplicated diabetes or hypertension are usually delivered in the early-term period, between 37⁺⁰ weeks and 40^+o weeks (7, 8).

Additional maternal disease, such as coagulopathies, cardiac pathology, or pulmonary pathology, poses a threat to mother or fetus if labour is left to start spontaneously in an uncontrolled set­ting. For example, if a patient has an active pulmonary embolus and is on anticoagulation therapy, an unplanned delivery may put the patient at risk of haemorrhage if timely discontinuation or change in anticoagulation therapy does not occur. Therefore, there is a whole subset of maternal pathologies that benefit from a controlled induc­tion of labour at a gestation age prior to 40⁺0 weeks or even prior to 39+o weeks when the likelihood of spontaneous labour increases significantly.

International cancer databases have provided a wealth of data on the many pregnancies that have been complicated by cancer. Each type of cancer has a specific gestational age at which delivery is indi­cated depending on its stage and progression, allowing the mother to return rapidly to her appropriate therapy regimen. Delivery is usually indicated when the risk to the mother becomes greater than the risk for the preterm neonate (9).

In the event of an IUFD, it is beneficial to induce delivery to protect the mother against infection or coagulopathy. As long as it is established that the mother's health is stable, and she has in­tact membranes, it is appropriate to offer the mother expectant management or induction of labour. Without intervention, 85% of women with an IUFD will deliver within 3 weeks. In the absence of abruption, pre-eclampsia, infection, or bleeding, the risk of an acquired coagulopathy is initially low. Although after 4 weeks only 10% of women will have developed coagulopathy, regular moni­toring of coagulation is still prudent. After that point the risk for bleeding and infection begin to rise and it is prudent to induce labour (10).

Prevention of fetal complications

From a fetal perspective, induction of labour is usually carried out in order to prevent IUFD. The risk of this may be related to a spe­cific maternal disease process (e.g. hypertension or diabetes), fetal diseases (e.g. IUGR or macrosomia), or to background risk factors such as maternal age, body mass index (BMI), or advanced gesta­tion. Specific maternal disease processes are covered elsewhere in this textbook.

Maternal obesity is an emerging problem throughout the world. As the medical community learns about the many facets of health af­fected by obesity it has become obvious that pregnancy complicated by obesity is at increased risk of IUFD. The trend for this phenom­enon begins at 40+o weeks, approximately 1-2 weeks prior to that of the remainder of the population.

Much like increasing BMI, increasing maternal age also has a cor­relation with increase in IUFD rates. It is generally accepted that over the age of 35 a woman is considered at risk of complications such as increased rates of aneuploidies. The rate of IUFD becomes statistically increased over the age of 40 with an odds ratio of 3.04 at 39 weeks in comparison to women aged 25-29 years (12). Many countries acknowledge that it is advisable to recommend induction of labour by 40+o weeks, and this is supported by a randomized trial which found no adverse effects on common outcomes of routine in­duction of women over the age of 35 at 39 weeks' gestation (13, 14). Whether this translates to fewer perinatal deaths remains unclear.

Oligohydramnios or insufficient amniotic fluid is defined by a single deepest pocket (without umbilical cord or fetal parts) meas­uring 2 cm or less or an amniotic fluid index of 5 cm or less (7). This condition is associated with uteroplacental insufficiency and resulting low fetal renal blood flow. In the initial evaluation of oligohydramnios, rupture of membranes must be ruled out regard­less of gestational age. Induction of labour is usually carried out if isolated oligohydramnios is detected at or beyond 36⁺⁰ weeks. In oligohydramnios of the preterm fetus, expectant management may be undertaken if fetal testing is feasible along with an investigation for additional aetiologies of oligohydramnios such as fetal anomalies (7). There is some emerging data that expectant management of iso­lated oligohydramnios at term does not change outcomes and may be a safe alternative to mandated induction (15).

Preterm prelabour rupture of membranes (PPROM) is defined as rupture of membranes prior to 37+o weeks in the absence of labour. In order to reduce the risk of sepsis, induction of labour is com­monly conducted once the pregnancy reaches 34 weeks, although randomized trials suggest that expectant management with close monitoring is also a safe option (16).

Intrauterine fetal growth restriction is defined as a composite es­timated fetal weight less than 10% for gestational age (although different sources may use different cut-offs or terminology). The general timing for delivery for these fetuses is debated, but it is gen­erally acceptable to deliver after 34+o weeks in the setting of growth restriction and abnormal fetal testing such as absent or reverse end- diastolic flow of the umbilical artery Doppler. Otherwise, in the set­ting of normal fetal testing, delivery is generally recommended after 37+o weeks, prior to 40+o weeks (18). According to current National Institute for Health and Care Excellence (NICE) guidelines, in the setting of severe growth restriction with concern for fetal com­promise, induction of labour is not indicated. In these settings, if delivery is indicated it is recommended to proceed with caesarean section (8).

Induction of labour is also sometimes recommended for fetal macrosomia, defined as 4000 g or 4500 g depending upon your source. Fetal macrosomia leads to significantly higher rates of IUFD, overall neonatal mortality, birth injury, neonatal asphyxia, failed in­duction of labour, meconium aspiration, and maternal birth injury (19). In a randomized controlled trial (RCT) conducted in France, Switzerland, and Belgium, 822 women with ultrasound-estimated fetal weight greater than the 95% centile were randomized to delivery between 37 and 38⁺⁶ weeks or expectant management. Induced ba­bies were 287 g lighter and were significantly more likely to be born vaginally. Furthermore, the risk of the composite outcome (signifi­cant shoulder dystocia, delay in delivery of the shoulder by >60 sec­onds, or fracture) was significantly reduced (by 68% from 6% to 2%). There was no difference in rate of caesarean section (20). This is the largest study of its kind; there are two additional RCTs which inves­tigate induction versus expectant management, however they both utilize 4000 g, they both had much smaller numbers, and they both induced at or close to 40 weeks which is likely why the data was less supportive of labour induction.

In the general population, a marked increase in IUFD occurs in ‘postdates pregnancies' The lowest perinatal death rate is at 38 weeks (1.9:1000) with the cumulative probability of death increasing to 5:1000 and 9:1000 at 42 and 43 weeks respectively (21). Additionally, there is an increase in multiple perinatal morbidities such as neo­natal convulsions, meconium aspiration, Apgar score less than 4, and admission to neonatal intensive care units. The NICE guide­line recommends induction of labour between 41+o and 42+o weeks. If a woman declines induction after 42+o weeks, twice-weekly fetal monitoring with cardiotocography and ultrasonography is recom­mended to reduce the risk of IUFD (8).

As discussed earlier, there are cases of maternal pathology that necessitate a timed delivery; the same can be said for fetal pathology. If there is a fetal anomaly or condition which requires immediate specialist postnatal care, it is often appropriate to perform an induc­tion prior to spontaneous labour. This ensures that the neonate can be born at a time when there are adequate staff and facilities to pro­vide optimal care. The timing of induction is best decided by the providers and should take into account the risks of prematurity, pro­longed pregnancy, and timed delivery.

In a pregnancy affected by isoimmunization (discussed elsewhere in this textbook), delivery depends upon the severity of fetal haem­olysis. If the fetus is stable and has not required intervention, in­duction of labour is appropriate at 37⁺o weeks or when fetal lung maturity is documented. In cases where the fetus has undergone multiple transfusions, induction is typically recommended around 32+o weeks (22, 23).

An indication of ‘bad obstetric history has been given as an indi­cation for induction for many years. It largely refers to a previous stillbirth, but may also include a history of recurrent miscarriage, abruption, prolonged infertility, or adverse fetal outcome in a pre­vious pregnancy. The rationale is that elective induction (often before the gestation of the previous event) will reduce the recurrence risk. While there is little hard evidence behind this, clinicians and women will be reassured by the data on social induction (discussed later in this chapter) that it does not increase the need for operative birth.