The complication of diabetes in pregnancy includes both pre-gestational diabetes (type 1 and type 2 diabetes mellitus) and gestational diabetes.

The adverse effect of type 1 diabetes on pregnancy is profound, but since the advent of synthetic insulin, outcomes have significantly improved from an era when the combination of type 1 diabetes and pregnancy was often a death sentence for mother and infant. While pregnancy outcomes are better for women with type 1 diabetes, the risk of complication is substantially higher than for non-diabetic women.1

Type 2 diabetes and its impact on pregnancy is becoming more apparent, with increasing rates of obesity in women of childbearing age. Women at risk often miss out on pre-pregnancy diagnosis, counselling and treatment.2

Increasing prevalence of gestational diabetes is linked to rates of obesity in the community and is also influenced by the changing demographics of the population, as ethnic background or country of birth effect the chance of diagnosis in pregnancy. Combined with changes to diagnostic thresholds, the number of women requiring additional education, monitoring and treatment for gestational diabetes has seen demands on clinicians grow.3

Women with type 1 and type 2 diabetes, and gestational diabetes to a lesser extent, are likely to develop a number of complications throughout pregnancy, but especially at term. For a woman, potential complications include caesarean delivery, operative vaginal birth and pre-eclampsia. Complications for the fetus might include macrosomia, shoulder dystocia, hypoglycaemia, jaundice and stillbirth.4 5

In the long-term, women with gestational diabetes remain at risk of developing type 2 (and type 1) diabetes over their lifetime. Their offspring are more likely to be obese and are susceptible to developing diabetes.6

Induction of labour

The principle of induction of labour is that early birth reduces the likelihood of developing complications that an ongoing pregnancy would potentially inflict on a woman with diabetes and her baby.

Induction is usually considered to be indicated where there is evidence that inducing labour leads to better outcomes for mother and child and does not result in an increase in undesirable effects, such as a higher caesarean section rate or more babies being admitted to the special care unit.

Pre-gestational diabetes and gestational diabetes increase the risk of hypertensive disorders of pregnancy, including pre-eclampsia. The diagnosis of these superimposed conditions is an additional clear indication for induction of labour to reduce the occurrence of maternal morbidity, such as severe hypertension or the progression of pre-eclampsia.7

Evidence base

While diabetes in pregnancy, especially gestational diabetes, is a relatively common clinical scenario, the lack of high-quality evidence to guide recommendations for induction of labour may be surprising.

Randomised controlled trials comparing induction of labour with expectant management for women with diabetes are few8 and the majority of evidence supporting induction of labour recommendations is gathered from cohort studies.9 10 11 Thankfully, the consistency of findings across a number of studies conducted in a range of countries and populations (most are from North America or Europe), gives confidence that we can provide adequate information to our patients.

Considerations regarding timing of delivery

The recommendations on timing of delivery, and thus induction, are informed primarily by cohort studies examining the risk of a particular outcome, such as caesarean section or stillbirth, occurring in a population of women with diabetes at each week of gestation, compared to women without any pregnancy complication.

Type 1 and type 2 diabetes

The risk of pregnancy complication for women with type 1 and type 2 diabetes is significantly greater than that of the general obstetric population and in women with gestational diabetes.12

Most importantly, the nadir for the rate of stillbirth for women with type 1 and type 2 diabetes was seen between 37 weeks and 38 weeks 6 days.13

Earlier delivery should be considered when end-organ complications are present, such as nephropathy, neuropathy and vasculopathy, or, when there is a poor obstetric history such as prior stillbirth.

Where significant fetal macrosomia is suspected in the presence of maternal diabetes, it is incumbent on clinicians to discuss the alternative of caesarean section, especially in light of the Montgomery v Lanarkshire case.14 While no guidelines go so far as to recommend caesarean delivery for any particular birth weight, the option of caesarean to prevent traumatic delivery could be considered when birth weight is estimated at greater than 4000–4500g.15

Gestational diabetes

In women with gestational diabetes, the lowest rate of stillbirth was seen in week 40, with a rise in the rate of stillbirth after 41 weeks greater than that observed in women without gestational diabetes.16 Cohort studies show lower rates of macrosomia in women with gestational diabetes delivered in week 38, with no increase, or even a reduction, in the incidence of caesarean section. The studies showed no reduction in the rate of shoulder dystocia.17 18 19 There is evidence of benefit from induction of labour for large-for-date fetuses, when clinically suspected and supported with ultrasound findings. The Boulvain study has shown a reduction in the risk of shoulder dystocia and fetal and maternal morbidity. Women with gestational diabetes were not excluded from this trial, making up approximately 10 per cent of the numbers included in the analysis.20

Methods of induction of labour

There is no evidence that a particular method of induction of labour for women with pre-gestational or gestational diabetes is preferred. Induction with prostaglandins and oxytocin were primarily used in the two randomised clinical trials. Mechanical methods with Foley balloon or double balloon are also used and may have benefits where concerns regarding fetal wellbeing mean that avoiding uterine hyperstimulation may be more desirable.

Key points

For women with pre-gestational or gestational diabetes, induction of labour may reduce the chance of common outcomes like macrosomia, shoulder dystocia and uncommon but important outcomes such as stillbirth.

The effect of induction of labour as a result of diabetes on the likelihood of caesarean section is probably neutral or may reduce the rate.

Timing for type 1 and type 2 diabetes is usually recommended after 37 and before 40 weeks, with the risk of stillbirth lowest between 37 and 39 weeks. For women with gestational diabetes requiring treatment with medication, (most commonly insulin), induction between 38 and 40 weeks is often recommended. Induction of labour around 40 weeks and up to 41 weeks is considered reasonable for women with gestational diabetes controlled by diet.

Suspected fetal macrosomia should trigger consideration of earlier induction of labour at early term (37–38 weeks), or if the risk of difficult vaginal delivery is substantial, then the option of caesarean section should be discussed with the patient.