What is the best blood glucose target for pregnant women who have type 1 or type 2 diabetes before becoming pregnant?

What is the issue?

Pregnant women with diabetes need to keep their blood glucose levels stable, using diet, exercise, insulin or other drugs, clinic visits and monitoring. This review looked at the best blood glucose target for pregnant women with diabetes.

Why is this important?

Women who have either type 1 or type 2 diabetes before they become pregnant have an increased risk of pregnancy loss, large babies, and babies dying. When a pregnant woman has high blood glucose and insulin resistance this can affect the development of the baby's heart and other organs. Babies born to diabetic mothers may also have a higher risk of developing obesity and type 2 diabetes.

Monitoring a diabetic pregnant woman's blood glucose level and staying within a target range may help to reduce these risks. We wanted to find out what the best blood glucose target is for pregnant women who had type 1 or type 2 diabetes before becoming pregnant.

What evidence did we find?

We found three small trials (in total 223 pregnant women with type 1 diabetes) looking at different blood glucose targets: very tight, tight, moderate, and loose. The quality of the studies and therefore the strength of the evidence was very low or low, so future research may change the results.

There were very few differences between very tight and tight-moderate blood glucose targets in two trials, although there were more cases of low blood glucose (hypoglycaemia) and longer hospital stays for women who had very tight blood glucose control.

A single trial compared tight, moderate, and loose blood glucose targets. In the loose target group, more women had pre-eclampsia, and there were more caesareans and large babies. There were few differences between the tight and moderate groups, although more women in the tight control group had low blood glucose in the first half of pregnancy.

What does this mean?

The evidence does not show much difference between moderate, tight and very tight blood glucose targets, although a loose blood glucose target may be worse for mothers and babies. However, the studies were small and the evidence is weak, so we do not yet know the best blood glucose target for women who have diabetes before becoming pregnant.

Authors' conclusions: 

In a very limited body of evidence, few differences in outcomes were seen between very tight and tight-moderate glycaemic control targets in pregnant women with pre-existing type 1 diabetes, including actual glycaemic control achieved. There is evidence of harm (increased pre-eclampsia, caesareans and birthweights greater than 90th centile) for 'loose' control (FBG above 7 mmol/L). Future trials comparing interventions, rather than glycaemic control targets, may be more feasible. Trials in pregnant women with pre-existing type 2 diabetes are required.

Read the full abstract...

The optimal glycaemic control target in pregnant women with pre-existing diabetes is unclear, although there is a clear link between high glucose concentrations and adverse birth outcomes.


To assess the effects of different intensities of glycaemic control in pregnant women with pre-existing type 1 or type 2 diabetes.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2016) and planned to search reference lists of retrieved studies.

Selection criteria: 

We included randomised controlled trials comparing different glycaemic control targets in pregnant women with pre-existing diabetes.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion, conducted data extraction, assessed risk of bias and checked for accuracy. We assessed the quality of the evidence using the GRADE approach.

Main results: 

We included three trials, all in women with type 1 diabetes (223 women and babies). All three trials were at high risk of bias due to lack of blinding, unclear methods of randomisation and selective reporting of outcomes. Two trials compared very tight (3.33 to 5.0 mmol/L fasting blood glucose (FBG)) with tight-moderate (4.45 to 6.38 mmol/L) glycaemic control targets, with one trial of 22 babies reporting no perinatal deaths or serious perinatal morbidity (evidence graded low for both outcomes). In the same trial, there were two congenital anomalies in the very tight, and none in the tight-moderate group, with no significant differences in caesarean section between groups (risk ratio (RR) 0.92, 95% confidence interval (CI) 0.49 to 1.73; evidence graded very low). In these two trials, glycaemic control was not significantly different between the very tight and tight-moderate groups by the third trimester, although one trial of 22 women found significantly less maternal hypoglycaemia in the tight-moderate group.

In a trial of 60 women and babies comparing tight (≤ 5.6 mmol/L FBG); moderate (5.6 to 6.7 mmol/L); and loose (6.7 to 8.9 mmol/L) glycaemic control targets, there were two neonatal deaths in the loose and none in the tight or moderate groups (evidence graded very low). There were significantly fewer women with pre-eclampsia (evidence graded low), fewer caesarean sections (evidence graded low) and fewer babies with birthweights greater than 90th centile (evidence graded low) in the combined tight-moderate compared with the loose group.

The quality of the evidence was graded low or very low for important outcomes, because of design limitations to the studies, the small numbers of women included, and wide confidence intervals crossing the line of no effect. Many of the important outcomes were not reported in these studies.