GEMS Study

The GEMS Study is examining the best criteria for testing for diabetes during pregnancy.

What is the GEMS study?

GEMS (Gestational Diabetes Mellitus Study of Diagnostic Thresholds) is a study to investigate how high blood sugar which starts during pregnancy - known as gestational diabetes mellitus (GDM) - 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.

What is GDM?

If a mother has GDM, it 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.

Why is the GEMS study important?

There have been no randomised trials comparing different ways of diagnosing 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 GDM 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 using the current threshold to diagnose GDM and the other using a 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 be among a small group of study participants who 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.

Take part in the GEMS Study

We’re recruiting 4,158 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, haven't done your glucose test for diabetes in pregnancy yet, and haven't had any form of diabetes before.  

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

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