Your LMC is required to recommend that you take a screening test, called a Polycose Test, for Gestational Diabetes Mellitis at around 26 – 28 weeks of pregnancy.

What is Gestational Diabetes Mellitis(GDM)?

Gestational diabetes means diabetes (a condition in which blood sugar/glucose isn’t properly regulated) that is first diagnosed during pregnancy. Between 2 – 10% of pregnant women test positive for gestational diabetes mellitis (GDM). For half of these women this glucose intolerance will be a temporary condition that is only present during pregnancy. About 50% of women who test positive for GDM probably already had undiagnosed diabetes mellitus before they became pregnant.

Many women will have higher than normal levels of blood sugar/glucose from time to time during pregnancy because pregnancy hormones suppress the release of the insulin (the hormone that regulates blood sugar levels), so that a pregnant woman’s blood sugar levels are hopefully consistently higher than the average adult’s. (Your baby needs a steady supply of glucose to meet her/his growth needs.) It is important that pregnant women eat regular small, healthy meals that provide for sustained glucose release rather than sugary snacks that cause short-term spikes in blood sugar levels.


To reduce your risk of developing gestational diabetes you should:-

  • Drink 5 – 8 glasses of water each day
  • Drink a maximum of 3 drinks per day that contain caffeine and sugar (including unsweetened fruit juice).
  • Exercise daily – make time for some low impact exercise each day e.g. walking, swimming, yoga, pilates. Research shows that 30+minutes of physical activity at least 3 times each week reduces pregnant women’s risk of developing gestational diabetes.
  • Eat regular small healthy meals – try to eat a meal that includes fresh vegetables, wholegrains and lean protein every 4 hours.
  • Snack between meals if you need to but stick to healthy snacks e.g. fresh fruit, nuts, low fat/low salt crackers and dips, carrots etc
  • Avoid processed food and takeaways because these are likely to be high in fat and salt, both of which make it harder for your body to metabolize sugar efficiently.
  • Vitamin D deficiency increases the risk of developing GDM.  Expose your skin to the sunlight with care for 30 minutes several times each week.  If you are unable to manage this, you may want to consider taking a Vitamin D3 supplement of between 1000 – 4000IU per day.

Risk Factors

Women who have the following risk factors are more likely to develop GDM or already have undiagnosed diabetes mellitus.

  • obesity
  • family history of diabetes
  • GDM in a previous pregnancy
  • previous stillbirth or unexplained neonatal death
  • a diet that consistently includes foods that have a high sugar content and are highly refined or processed and that lacks at least 5 servings of fresh vegetables and fruit daily.
  • rapid, excessive weight gain in pregnancy

It is recommended that women with these risk factors and women who experience a rapid and excessive weight gain during pregnancy and spill sugar into their urine on two consecutive days are tested for GDM.

Some health professionals believe that all women of non-European ethnicity should be screened for GDM because all forms of diabetes are more common amongst Maori, Pacific Island, Indian and Asian peoples in NZ/Aotearoa.

Some LMCs recommend screening for GDM for all their pregnant clients because about 50% of women who have GDM will have no symptoms or risk factors and because the incidence of diabetes mellitus and the health risks associated with this disease is increasing throughout the population.  However, at this time there is no evidence that such routine screening improves outcomes for mothers and babies.

What are the risks?

If insulin regulation of blood sugar is not working well because a woman has diabetes mellitus or has developed gestational diabetes, her baby may grow to be much bigger than the average, increasing the risk of birthing difficulties and complications in the hours/days immediately after birth. There is also a concern that if a baby has been continually exposed to high blood sugar levels in utero, that they may not be able to sustain this after birth (when s/he is no longer receiving nutrients from his mother’s blood) and her/his blood sugar levels may drop quickly and dangerously immediately after birth.

Polycose Testing or Glucose Screening in Pregnancy

This test is carried out in a medical laboratory or hospital. You will be asked to drink a liquid containing 50 mg of polycose (a type of sugar). One hour later a sample of blood is taken to see how well your body has metabolized this sugar. If your result shows that your blood glucose level is higher than 7.8mol/ml, you will be asked to take a Glucose Tolerance Test (GTT).

This one-hour polycose screening test has a high false positive rate. Approximately 15 – 20% of pregnant women test positive on the polycose test although only 2 – 5% will have any form of diabetes.  If you are at at risk of having GDM, your LMC may recommend missing out the Polycose test and taking a GTT, which has a much lower rate of false positive results meaning that you will only have to have one sugary drink.

The accuracy of the polycose screening test is improved if: –

  • you have eaten a small, healthy, non-sugary meal an hour or so before undergoing the test.
  • during the hour between having the drink and giving the blood sample you walk around so that your body is assisted to metabolize the sugar you have drunk.
  • you have not been ill or vomiting in the 24 hours before taking the test.
  • you are feeling well-rested and relaxed.

In the hour between drinking the polycose and having your blood sample taken, it is also important that you do not:-

  • have a cup of ordinary tea, coffee or hot chocolate, cordial, energy drink or soft drink e.g. coca cola etc.
  • eat any sugary food – e.g. cakes, biscuits, candy bars, muesli bars, icecream etc.
  • smoke cigarettes

Because you’re going to be waiting around for an hour you will need to bring a book, magazine, ipod, laptop so that you’ve got something to do to fill in the time.

Glucose Tolerance Test (GTT)

This test is also carried out in a medical laboratory and is usually recommended if you have a positive result from the polycose test or the early pregnancy HbA1c.

You should book to have this test first thing in the morning, because you will be asked not to eat or drink anything except water for at least 8 hours before taking the test. A blood sample will be taken when you arrive at the lab to measure your fasting blood glucose levels, then you will be asked to drink a liquid containing 75mg of glucose. Another blood sample is taken after 2 hours.

Because you’re going to be waiting around for two hours, you will need to bring a book, magazine, ipod, laptop etc so that you’ve got something to do to fill in the time.

If your first blood sample showed a blood glucose level of greater than 5.5mmol/l and the second was above 9mml/l you will be diagnosed as having gestational diabetes.

Safety and Accuracy

There are question-marks over the safety and accuracy of the GTT. Most pregnant women find fasting overnight and for the duration of this test a challenge. Very few pregnant women would ingest 75mg of glucose solution in one hit at any time much less on an empty stomach – so it possible that challenging women’s body in this way could produce an inaccurate result. Many women find the combination of fasting and glucose produces headaches, nausea or bloating.


If you are diagnosed with gestational diabetes, you will be advised to reduce your intake of dietary sugar and given help with meal planning etc. You will be shown how to test and record your blood glucose levels at home, several times each day, so that you can monitor how well the changes in your diet are controlling your diabetes.

If your blood glucose readings remain consistently above normal, you may need to self inject insulin (the hormone that controls your blood sugar levels) or be prescribed an oral medication called metformin.

Women who have diabetes during pregnancy are often advised to have their labours induced at between 38 – 40 weeks in an effort to avoid the risk of birth complications and metabolic problems for the newborn baby. If a combination of  dietary change and regular exercise has enabled you to keep your blood sugar levels within the normal range there is no benefit (and some risks) associated with induction of labour.


If you are diagnosed with gestational diabetes you will be offered a blood test during the first 24 hours after you’ve given birth and another 6 weeks after you’ve given birth to check that your blood sugar levels have returned to normal.

Up to 50% of women who are diagnosed with GDM will develop non-insulin dependent diabetes at some stage in their lives. If you have been diagnosed with GDM you are advised to continue to follow the advice you were given about diet and exercise during pregnancy and to have your blood glucose levels tested each year.