Liggins Institute

GEMS Study

GEMS is a study that is trying to find out whether the current criteria used to diagnose diabetes in pregnancy in New Zealand is best, or whether we should be using a lower blood glucose threshold for detection.

GEMS logo

What is the GEMS study?

GEMS stands for Gestational Diabetes Mellitus Study of Diagnostic Thresholds. It is a study to investigate how gestational diabetes mellitus (GDM), which is diabetes that develops in pregnancy, should be diagnosed. We are trying to find out whether the current criteria used to diagnose GDM in New Zealand is best, or whether we should be using a lower blood glucose threshold for detection.

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What is gestational diabetes mellitus?

High blood sugar which starts during pregnancy is known as gestational diabetes mellitus or GDM. If a mother has GDM, this can cause health problems for her and her baby during pregnancy and birth. Babies born to mothers with GDM may be large-for-gestational age, suffer birth injuries, breathing problems, jaundice and low blood sugar.

Long-term health risks to the mother include an increased risk of developing Type 2 diabetes and heart disease. Babies born to mothers with GDM have an increased risk of growing up overweight or obese and of developing diabetes in adulthood.

In New Zealand, the Ministry of Health recommends that all pregnant women are tested for GDM.

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Why is the GEMS study important?

There have been no randomised trials comparing these different ways of diagnosing gestational diabetes mellitus (GDM) before. GEMS will find out which blood sugar concentrations are the most appropriate for diagnosing GDM to try to reduce the health problems it can cause.

By participating in GEMS, you will be actively contributing to our understanding of GDM, which will benefit pregnant women and their children.

Better understanding is important because gestational diabetes not only impacts on the health of the mother and baby during and just after birth but also on the long-term health of the mother and the infant.


What does participation in the study involve?

If you choose to participate in GEMS, you will be randomly assigned to one of two study groups – one which uses the current threshold to diagnose GDM, and the other which uses the lower threshold. As is normal during pregnancy, your midwife will test you for GDM. In GEMS, that's with an Oral Glucose Tolerance Test. You’ll also be asked to complete a questionnaire about your diet, activity patterns, health and wellbeing.

You may have a blood sample and body measurements taken when you enter the study, at 36 weeks’ pregnant, and when your baby is six months old. After the birth, a blood sample from the placental umbilical cord and body measurements may also be collected.

Who can take part?

We’re recruiting 9,000 pregnant women planning to give birth in the Auckland District Health Board (ADHB) and Counties Manukau District Health Board (CMDHB). You can participate if you are pregnant with one baby and less than 34 weeks pregnant when you have your Oral Glucose Tolerance Test, do not have diabetes mellitus or a previous history of GDM, and give your written consent.

How do I take part?

Enrolling is easy - the GEMS team can do it for you. Simply call us on 09 923 1356 or email your name, phone number and expected due date to We'll get back to you quickly!  

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What happens if I change my mind?

Taking part in this study is entirely your choice. If you don’t want to take part, you don’t have to give a reason, and it will not affect the care you receive. If you do want to take part now, but change your mind later, you can leave the study at any time.

Find out more

If you would like to talk to one of our research midwives about GEMS, please call 09 923 1356 or email us at


GEMS participant information brochure
Download the GEMS participant information leaflet (113.4 kB, PDF)