GEMS Study

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

Five pregnant women

What is the GEMS study?

This study has completed recruitment. We appreciate the support we received from pregnant women and Lead Maternity Carers for this important research.

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.

Fundal height of pregnant woman being measured

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.

Participants in GEMS are 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?

Participants in GEMS are 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 involved an Oral Glucose Tolerance Test. Women were also asked to complete a questionnaire about their diet, activity patterns, health and wellbeing.

A small group of study participants are also selected to have a blood sample and body measurements taken on entry to the study, at 36 weeks pregnant, and when baby is six months old. After the birth, a blood sample from the placental umbilical cord and body measurements may also be collected.

Baby being breastfeed

Take part in the GEMS Study

More than 4,000 pregnant women planning to give birth in the Auckland District Health Board (ADHB) and Counties Manukau District Health Board (CMDHB) are participating in GEMS. Women were able to participate if pregnant with one baby, they hadn’t done their glucose test for diabetes in pregnancy yet, and they hadn’t had any form of diabetes before.

What happens if I change my mind?

Taking part in this study is entirely your choice. If you no longer wish to take part, you don’t have to give a reason, and it will not affect the care you receive. You can leave the study at any time.

Find out more

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

When will the results of the GEMS Study be available?

The final participants of the GEMS Study will give birth in mid-2020. We expect to have results for the study by the end of 2020.