What is the issue?

The aim of this Cochrane review was to find out the effectiveness and safety of insulin compared with oral medication or non-pharmacological interventions for the treatment of gestational diabetes mellitus (GDM, which is diabetes diagnosed in pregnancy). It also looked at different timings for taking insulin during the day. We collected all the relevant studies (May 2017) and analysed the data.

Why is this important?

GDM can lead to both short- and long-term complications for the mother and her baby.

Usually, diet and lifestyle advice is the first step, and women whose blood glucose remains too high may be treated with insulin, which is normally injected every day.

Finding out if other treatment options are as safe and effective as insulin, is important, as these other treatments may be preferred by women who do not want to inject themselves with insulin.

What evidence did we find?

We searched for evidence on 1 May 2017 and found 53 studies reporting data for 7381 mothers and 46 studies reported data for 6435 babies. Overall, the quality of the evidence ranged from very low to moderate. Studies were undertaken in a variety of countries, including low-, middle- and high-income countries. Three studies reported that financial support or drugs had been provided by a pharmaceutical company and 36 studies did not provide any statement about the source of funding.

For mothers with GDM, insulin was associated with an increased likelihood of hypertensive disorders of pregnancy (high blood pressure – not defined) although there was no evidence of any difference in pre-eclampsia (high blood pressure, swelling and protein in the urine), birth by caesarean section, developing type 2 diabetes, or postnatal weight when women who had been treated with insulin were compared with women who had been treated with oral anti-diabetic medication.

Insulin appeared to possibly increase the likelihood of induction of labour, when compared with oral anti-diabetic medication but these results are unclear. Damage to the perineum, return to pre-pregnancy weight or postnatal depression were not reported by the included studies. For the baby, there was no evidence of a clear difference between groups in the risk of being born large-for-gestational age, death or serious illness after birth, low blood sugar, being overweight as a baby or as a child, having a hearing or visual impairment, or mild developmental delay at 18 months. None of the included studies looked at the baby’s health in childhood.

We also looked at comparisons for regular human insulin versus other insulin types, insulin versus dietary advice with standard care, insulin versus exercise, and we also looked at comparisons of different insulin dosages and frequency. However, there was not enough evidence for us to be certain of any differences for many of the key health outcomes.

What does this mean?

The available evidence suggests that there are very few differences in short-term outcomes for the mother and baby between treatment with injected insulin and treatment with oral medication. There is not enough evidence yet for the long-term outcomes. Decisions about which treatment to use could be based on discussions between the doctor and the mother. Further research is needed to explore optimal insulin regimens for women with GDM. Future studies could aim to report long-term as well short-term outcomes for mothers and their babies.