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Pregnant women with type 1 diabetes who used a continuous glucose monitoring system were half as likely to have a large baby compared with those using standard finger prick blood glucose measurements. Only 15% of infants needed intensive care admissions due to low blood glucose in the continuous glucose monitoring group, compared with 28% born to mothers in the standard finger prick control group.

Pregnant women using continuous monitoring spent 7% more time in the target glucose range than those on standard measurements. However, their HbA1c levels, which indicate diabetic control over 12 weeks, only improved slightly. This may be unsurprising because HbA1c results are less reliable in pregnancy and women found it hard to stick to the continuous monitoring protocol.

Strict control of blood glucose levels during pregnancy reduces the risk for women with type 1 diabetes, and their babies are less likely to be large or need treatment for low blood glucose. Continuous monitoring provides many readings but requires the user to deliver insulin accordingly. Motivated women may find continuous monitoring helps them manage their glucose levels more closely during pregnancy and reduce both antenatal and postnatal complications.

Why was this study needed?

Up to 5% of women giving birth in England and Wales, each year have diabetes. Of these, 7.5% have type 1 diabetes.

Women with type 1 diabetes are at higher risk of complications in pregnancy mainly because glucose levels are harder to control. Their babies are more likely to be larger than average, which can mean a difficult delivery, and need special care when born. The cost of a baby’s neonatal intensive care stay is £1,118 per day in the UK.

A continuous glucose monitoring system gives multiple glucose readings, day and night, via a sensor placed under the skin. It is different to an insulin pump, which delivers the drug. Continuous monitoring provides more data than finger prick blood glucose measurements.

Previous studies recruited low numbers and provided weak evidence, so the authors wanted to design a larger study. This study aimed to see if pregnant women on insulin could control their blood sugar levels better using these devices and if there was an improvement in maternal and newborn health outcomes.

What did this study do?

This randomised controlled trial, CONCEPTT, took place in 31 hospitals in seven high-income countries, including England and Scotland.

Pregnant women with type 1 diabetes (215) and women planning to get pregnant (110), in separate groups, were randomised to use continuous glucose monitoring or finger prick glucose monitoring.

Diabetes teams trained participants to use the continuous monitoring devices. Both groups were instructed to take at least seven finger prick readings per day; the intervention group did this to verify the machine readings before administering insulin.

Nearly half of pregnant participants used an insulin pump instead of multiple injections. In the UK, only 6% of non-pregnant people with type 1 diabetes use insulin pumps. The groups were treated equally; however, there were more unscheduled nurse visits in the intervention group due to technical problems.

What did it find?

  • Pregnant women using continuous glucose monitoring had lower HbA1c levels at 34 weeks. Levels decreased from 51mmol/mol (6.83%) at baseline to 46mmol/mol (6.35%) at 34 weeks of pregnancy, compared to the control group, which dropped from 52mmol/mol (6.95%) to 48mmol/mol (6.53%). This indicates a slightly better control of blood glucose levels for women using continuous monitoring. There was no significant difference in change of HbA1c levels in the planning pregnancy groups.
  • Pregnant women at 34 weeks of pregnancy using continuous monitoring spent more of their time, 68% (which equates to one hour 41 minutes more per day), in the recommended glucose control range of 3.5 to 7.8 mmol/L compared to those in the control group who spent 61% of the time in the target glucose control range. At baseline, both groups spent 52% in target glucose control range.
  • Newborns were less likely to be larger than average if they were born to mothers using continuous monitoring than to mothers who used finger prick blood glucose monitoring only (odds ratio [OR] 0.51, 95% CI 0.28 to 0.90). Rates were high in both groups though, with 36% of babies born in the continuous monitoring group extremely large for gestational age compared to 44% in the standard group. They were also less likely to be admitted to neonatal intensive care for more than 24 hours, 27% admitted compared to 43% (OR 0.48, 95% CI 0.26 to 0.86). Fewer newborns born to this group experienced a drop in blood glucose that needed treatment, 15% versus 28% (OR 0.45, 0.22 to 0.89).
  • There were no significant differences between the groups for patient-reported outcomes such as quality of life.
  • There were 109 adverse events experienced by 107 women randomised to continuous monitoring and 78 adverse events experienced by 107 women in the control group (relative risk [RR] 1.4, 95% CI 1.0 to 1.8). The most common events were skin reactions and problems with the continuous monitoring device. Few significant serious adverse events took place. Sticking to the continuous monitoring protocol appeared to be difficult for women as 30% of pregnant women did not achieve it more than 75% of the time.

What does current guidance say on this issue?

NICE 2008 guidance recommends that clinicians do not offer continuous glucose monitoring routinely to pregnant women with diabetes. It advises to consider it for some pregnant women taking insulin. This includes pregnant women on insulin therapy who have unstable blood glucose levels or have problems with severe low blood glucose episodes.

What are the implications?

Improved newborn health outcomes with continuous glucose monitoring are probably due to better glucose control in pregnancy.

There could be a role for continuous monitoring use by pregnant women with type 1 diabetes, but this may depend on individual preferences. Participants selected for this trial are likely to be more motivated than average because they had to meet eligibility criteria for using continuous monitoring consistently. Device placement can also irritate skin, and continuous readings may heighten anxiety.

Economic analyses are needed to justify the costs of the system and trained support required. There is scope for further patient outcome results which may help inform patient choice.

Citation and Funding

Feig DS, Donovan LE, Corcoy R, et al; CONCEPTT Collaborative Group. Continuous glucose monitoring in pregnant women with type 1 diabetes (CONCEPTT): a multicentre international randomised controlled trial. Lancet. 2017;390(10110):2347-59.

This project was funded by the National Institute for Health Research, Juvenile Diabetes Research Foundation and Canadian Clinical Trials Network.


Diabetes UK. HbA1c calculator. London; Diabetes UK. Accessed 2017.

NHS Choices. Type 1 diabetes. Department of Health: London; 2016

NICE. Diabetes in pregnancy: management from preconception to the postnatal period. NG3. London: National Institute for Health and Care Excellence; 2015.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre

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Continuous glucose monitoring systems are small devices worn just underneath the skin and measure glucose levels every few minutes. There are different types of devices available. Either they measure glucose levels in real time with the user being able to check the devices anytime, or they store the results and the user, or healthcare professional, can download the data and look back at the results to see trends. A continuous monitoring device has to be calibrated using finger prick blood glucose levels usually at least twice a day. The device is changed every seven days. The sensor does not deliver insulin.


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