Gestational diabetes mellitus (GDM) is associated with short‐ and long‐term complications
for the mother and her infant. Women who are unable to maintain their blood glucose
concentration within pre‐specified treatment targets with diet and lifestyle interventions
will require anti‐diabetic pharmacological therapies. This review explores the safety
and effectiveness of insulin compared with oral anti‐diabetic pharmacological therapies,
non‐pharmacological interventions and insulin regimens. To evaluate the effects of
insulin in treating women with gestational diabetes. We searched Pregnancy and Childbirth's
Trials Register (1 May 2017), ClinicalTrials.gov , WHO International Clinical Trials
Registry Platform ( ICTRP ) (1 May 2017) and reference lists of retrieved studies.
We included randomised controlled trials (including those published in abstract form)
comparing: a) insulin with an oral anti‐diabetic pharmacological therapy; b) with
a non‐pharmacological intervention; c) different insulin analogues; d) different insulin
regimens for treating women with diagnosed with GDM. We excluded quasi‐randomised
and trials including women with pre‐existing type 1 or type 2 diabetes. Cross‐over
trials were not eligible for inclusion. Two review authors independently assessed
study eligibility, risk of bias, and extracted data. Data were checked for accuracy.
We included 53 relevant studies (103 publications), reporting data for 7381 women.
Forty‐six of these studies reported data for 6435 infants but our analyses were based
on fewer number of studies/participants. Overall, the risk of bias was unclear; 40
of the 53 included trials were not blinded. Overall, the quality of the evidence ranged
from moderate to very low quality . The primary reasons for downgrading evidence
were imprecision, risk of bias and inconsistency. We report the results for our maternal
and infant GRADE outcomes for the main comparison. Insulin versus oral anti‐diabetic
pharmacological therapy For the mother, insulin was associated with an increased risk
for hypertensive disorders of pregnancy (not defined) compared to oral anti‐diabetic
pharmacological therapy (risk ratio (RR) 1.89, 95% confidence interval (CI) 1.14 to
3.12; four studies, 1214 women; moderate‐quality evidence). There was no clear evidence
of a difference between those who had been treated with insulin and those who had
been treated with an oral anti‐diabetic pharmacological therapy for the risk of pre‐eclampsia
(RR 1.14, 95% CI 0.86 to 1.52; 10 studies, 2060 women; moderate‐quality evidence
); the risk of birth by caesarean section
(RR 1.03, 95% CI 0.93 to 1.14; 17 studies, 1988 women; moderate‐quality evidence
); or the risk of developing type 2 diabetes (metformin only) (RR 1.39, 95% CI 0.80
to 2.44; two studies, 754 women; moderate‐quality evidence ). The risk of undergoing
induction of labour for those treated with insulin compared with oral anti‐diabetic
pharmacological therapy may possibly be increased, although the evidence was not clear
(average RR 1.30, 95% CI 0.96 to 1.75; three studies, 348 women; I² = 32%; moderate‐quality
of evidence ). There was no clear evidence of difference in postnatal weight retention
between women treated with insulin and those treated with oral anti‐diabetic pharmacological
therapy (metformin) at six to eight weeks postpartum (MD ‐1.60 kg, 95% CI ‐6.34 to
3.14; one study, 167 women; low‐quality evidence ) or one year postpartum (MD ‐3.70,
95% CI ‐8.50 to 1.10; one study, 176 women; low‐quality evidence ). The outcomes
of perineal trauma/tearing or postnatal depression were not reported in the included
studies. For the infant, there was no evidence of a clear difference between those
whose mothers had been treated with insulin and those treated with oral anti‐diabetic
pharmacological therapies for the risk of being born large‐for‐gestational age (average
RR 1.01, 95% CI 0.76 to 1.35; 13 studies, 2352 infants; moderate‐quality evidence
); the risk of perinatal (fetal and neonatal death) mortality (RR 0.85; 95% CI 0.29
to 2.49; 10 studies, 1463 infants; low‐quality evidence );, for the risk of death
or serious morbidity composite (RR 1.03, 95% CI 0.84 to 1.26; two studies, 760 infants;
moderate‐quality evidence ); the risk of neonatal hypoglycaemia (average RR 1.14,
95% CI 0.85 to 1.52; 24 studies, 3892 infants; low‐quality evidence ); neonatal
adiposity at birth (% fat mass) (mean difference (MD) 1.6%, 95% CI ‐3.77 to 0.57;
one study, 82 infants; moderate‐quality evidence ); neonatal adiposity at birth
(skinfold sum/mm) (MD 0.8 mm, 95% CI ‐2.33 to 0.73; random‐effects; one study, 82
infants; very low‐quality evidence ); or childhood adiposity (total percentage fat
mass) (MD 0.5%; 95% CI ‐0.49 to 1.49; one study, 318 children; low‐quality evidence
). Low‐quality evidence also found no clear differences between groups for rates of
neurosensory disabilities in later childhood : hearing impairment (RR 0.31, 95% CI
0.01 to 7.49; one study, 93 children), visual impairment (RR 0.31, 95% CI 0.03 to
2.90; one study, 93 children), or any mild developmental delay (RR 1.07, 95% CI 0.33
to 3.44; one study, 93 children). Later infant mortality, and childhood diabetes were
not reported as outcomes in the included studies. We also looked at comparisons for
regular human insulin versus other insulin analogues, insulin versus diet/standard
care, insulin versus exercise and comparisons of insulin regimens, however there was
insufficient evidence to determine any differences for many of the key health outcomes.
Please refer to the main results for more information about these comparisons. The
main comparison in this review is insulin versus oral anti‐diabetic pharmacological
therapies. Insulin and oral anti‐diabetic pharmacological therapies have similar effects
on key health outcomes. The quality of the evidence ranged from very low to moderate,
with downgrading decisions due to imprecision, risk of bias and inconsistency. For
the other comparisons of this review (insulin compared with non‐pharmacological interventions,
different insulin analogies or different insulin regimens), there is insufficient
volume of high‐quality evidence to determine differences for key health outcomes.
Long‐term maternal and neonatal outcomes were poorly reported for all comparisons.
The evidence suggests that there are minimal harms associated with the effects of
treatment with either insulin or oral anti‐diabetic pharmacological therapies. The
choice to use one or the other may be down to physician or maternal preference, availability
or severity of GDM. Further research is needed to explore optimal insulin regimens.
Further research could aim to report data for standardised GDM outcomes. 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.