Gestational Diabetes

Gestational diabetes affects between 3-6% of all pregnancies (1). However, rising obesity levels and women choosing to have children later in life (both risk factors for gestational diabetes) could see an increase in this rate in the future. It is important that gestational diabetes is addressed as women diagnosed are at higher risk of developing diabetes following pregnancy, as are their offspring.

Gestational diabetes is defined as diabetes which first occurs or is first identified during pregnancy. It, therefore, includes cases in which a woman has developed diabetes due to pregnancy but also those women with existing diabetes that had not previously been diagnosed.

Diabetes is a disease characterised by high blood glucose levels. Normally in the body the hormone insulin (produced by the pancreas) allows the glucose in the blood to move into the body’s cells where it is used for energy. In a person with diabetes not enough insulin is being produced or the body is not using the insulin properly and glucose builds up in the bloodstream.

There are several processes during pregnancy which affect insulin and blood glucose levels. A woman’s energy requirements are higher at this time so more insulin is required to move the glucose from the blood into the cells. From approximately 24 weeks in pregnancy the insulin needed is two to three times higher than normal. Women most commonly develop gestational diabetes between the 24th-28th week of pregnancy.

In addition, the placenta produces hormones which, while helping the baby to grow, also block the action of the mother’s insulin. This is referred to as insulin resistance. All pregnant women develop insulin resistance at some stage but most are able to produce higher amounts of insulin to overcome it. Those who are unable to increase their insulin production develop gestational diabetes (2).

Women with gestational diabetes will have their blood glucose levels tested again approximately 6-8 weeks after delivery. For most women, the condition goes away after the baby is born when a woman’s insulin needs return to pre-pregnancy levels. However, women who have gestational diabetes are at increased risk of developing Type 2 diabetes later in life.

Who is at risk?

• Ethnic group - Indigenous Australian, Pacific Islander, South or East Asian or Middle-Eastern women
  
• Family history - parent or sibling with Type 2 diabetes
  
• Obesity - women who have a body mass index of 30 or more
  
• Age - women who are aged 35 or over
  
• Previous glucose intolerance (including previous gestational diabetes)
  
• Women who have given birth to a baby over 4kg

Implications for the pregnant woman

Gestational diabetes is associated with a number of problems during pregnancy. Pre-eclampsia or pregnancy induced hypertension (high blood pressure) is higher in women with gestational diabetes. If untreated, pre-eclampsia can lead to complications for both mother and baby. Women are also more likely to experience bladder infections.

Women with gestational diabetes are also more likely to have a baby of larger weight (above 4kg or 8lb 13 oz). This is because glucose crosses the placenta, raising glucose levels in the baby’s blood. These high glucose levels stimulate the baby’s pancreas to produce more insulin which in turn makes the baby grow larger. Having a larger baby means a woman has an increased risk of damage to the pelvic floor and of having a Caesarean section.

Implications for the baby

The main implication is that the baby will weigh more (see above). Being larger means the baby is at higher risk of shoulder dystocia during a vaginal delivery. Shoulder dystocia occurs when the baby’s shoulder or shoulders become stuck after the delivery of the baby’s head.

Women who are pregnant with larger babies have a higher chance of having their baby delivered early. Although the baby may be large in size when it is born this does not mean it is fully developed. These babies, therefore, may experience problems associated with premature birth (eg. jaundice, respiratory problems).

After the baby is born it is no longer exposed to the mother’s high glucose levels but will still be producing high amounts of insulin. Consequently, low blood glucose (hypoglycemia) can result in the first few days. Babies born to women with gestational diabetes will have their glucose levels carefully monitored. A baby may be given glucose intravenously if required.

Babies born to women who develop diabetes during their pregnancy are not generally at risk of birth defects as the diabetes usually occurs between week 24 and week 28 (developmental abnormalities usually occur in the first trimester). However, for women who had undiagnosed diabetes before becoming pregnant, the baby does have a higher risk of birth defects. Early diagnosis of diabetes is important for anyone but especially for women planning to fall pregnant.

Diagnosis

While the medical community was aware that gestational diabetes could result in health problems, it had previously not been established if screening all women for the condition during pregnancy and treating affected women was of value. There were concerns that identifying women with gestational diabetes might in fact lead to an increase in medical intervention, without any corresponding benefit (3). However, with the publication of results from the Australian Carbohydrate Intolerance in Pregnancy Study (ACHOIS) in June 2005, this issue has become clearer (4).

ACHOIS randomised 1000 women with gestational diabetes to either routine antenatal care or to an intervention that included home glucose monitoring, review by a diabetes educator, dietician and physicians, and insulin therapy if glycaemic targets were not met. Results showed the rate of “serious perinatal complications” was significantly higher in the women who received routine antenatal care compared to those in the intervention group (4% versus 1%) (5). While women in the intervention group were more likely to have their labour induced, there was no increase in the caesarean rate. In addition, women in the intervention group reported lower rates of depression and higher health-related quality of life scores than the routine care group (6).

While the current statement on the diagnosis of gestational diabetes from the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) states it “takes no position on the merits of routine screening [for gestational diabetes]”; if employed the RANZCOG supports “uniformity in testing used and the subsequent follow up” (7). (It should be noted that the RANZCOG statement was released prior to the ACHOIS findings and is up for review in November 2006).

If screening occurs it should take place between week 26 and 28 of the pregnancy. Women should undergo what is referred to as a glucose challenge test (GCT). This involves drinking a glucose drink and then having a blood test one hour later to measure blood glucose levels. If the test is positive then an oral glucose tolerance test (OGTT) is carried out. This test involves taking a blood sample before and then two hours after the glucose drink.

Women who are at high risk of gestational diabetes (see ‘Who is at risk?’) should undergo testing for the condition as soon as feasible in their pregnancy. If the test is negative they should be retested again between 26-28 weeks of gestation.

A further study, the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study is also underway and will hopefully answer more questions on gestational diabetes. Results from this study are expected in mid 2007 (8).

Treatment

There are three strategies for the treatment of gestational diabetes:

Monitoring blood glucose levels
Women with gestational diabetes will need to check their blood glucose levels regularly. The medical practitioner will provide the ‘healthy range’ for blood glucose levels and advise how often blood glucose levels should be tested each day. Controlling blood glucose levels is extremely important for the health of the woman and her baby.

Testing blood glucose levels involves pricking the finger with a very small needle to obtain a drop of blood. The blood is then placed on a strip and inserted into a blood glucose meter (device used to measure blood glucose levels).

Diet
Women with gestational diabetes should consult a dietician for dietary advice. This will ensure that dietary modifications help manage the gestational diabetes but also provide the essential nutrients required during pregnancy. Some general guidelines include:

• Eat small meals regularly to keep blood glucose levels stable
  
• Include foods which rate low on the glycaemic index (GI) (for more information see http://www.glycemicindex.com)
  
• Moderate carbohydrate intake
  
• Eat a diet rich in fibre
  
• Lower the intake of fat, particularly saturated fat.

Exercise
When we exercise, glucose is transported to the cells for energy use, lowering the amount of glucose present in the blood. Exercise, therefore, plays an important role in treating gestational diabetes. Women without medical or obstetric complications, can continue with a moderately physical exercise program during pregnancy. Those women who were not physically active prior to their pregnancy should be encouraged to begin an exercise program but to avoid starting a vigorous exercise program at this time. Women should discuss their exercise program with their medical practitioner.

Apart from lowering blood glucose levels, exercise in pregnancy is beneficial for a number of other reasons. It can, for example, reduce some of the symptoms women experience during pregnancy (sleeping difficulties, constipation, fatigue and backache).

Medications
For some women, dietary modifications and exercise will not be sufficient to reduce blood glucose levels and they will need to have insulin injections. Insulin does not cross the placenta and so will not affect the unborn baby. Other drugs used in treating diabetes (eg. oral antidiabetic drugs) are generally not recommended for use in pregnancy.

Future pregnancies and long term considerations

It is estimated that a woman who has gestational diabetes has a 30-69% chance of developing the condition again in subsequent pregnancies (9). Risk factors for experiencing such a recurrence include a large baby in the initial pregnancy, obesity in the mother, early diagnosis of gestational diabetes and/or need for insulin during the initial pregnancy, age and increase in pre-pregnancy weight between pregnancies (10).

As the rate of recurrence of gestational diabetes in subsequent pregnancies is significant it is important that women who are still of reproductive age are counselled on planning future pregnancies. This allows for modifiable risk factors like obesity to be addressed, hopefully reducing the risk of a recurrence of gestational diabetes.

Women who have gestational diabetes are also at risk of developing Type 2 diabetes later in life. Similarly, children born to a woman with gestational diabetes have a higher risk of obesity, impaired glucose intolerance and Type 2 diabetes as children and adults. Women with a history of gestational diabetes and their children should, therefore, follow a healthy diet and participate in regular exercise. Women will be instructed by their medical practitioner as to how often they will be required to have their blood glucose levels tested (from every year to every two to three years).

Breastfeeding

There is no reason why women with gestational diabetes cannot breast feed their baby. As breastfeeding often helps women lose the extra weight gained during pregnancy, it can also play a role in reducing the risk of developing diabetes later.

References

1. Tuffnell DJ, West J & Walkinshaw SA. Treatments for gestational diabetes and impaired glucose tolerance in pregnancy Cochrane Database Syst Rev 2003; 3:CD003395
2. McElduff, A. Gestational diabetes mellitus Med Obs 24 March 2006; 29-31
3. Tuffnell DJ, West J & Walkinshaw SA
4. Crowther , CA et al. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes New Eng J Med 2005; 352:2477-2486
5. Crowther , CA et al. Ibid
6. Fraser, R. Gestational diabetes: After the ACHOIS trial Diabet Med 2006; 23:1-27
7. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) College Statement: Diagnosis of Gestational Diabetes November 2004
8. HAPO Study Cooperative Group. The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study Int J Gynaecol Obstet 2002; 78:1:69-77
9. MacNeill, S et al. Rates and risk factors for recurrence of gestational diabetes Diabetes Care 2001; 24:4:659-62
10. MacNeill, S et al. Ibid

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This article was written by Kirsten Braun and reviewed by the Editorial Committee for Health Journey, Vol 2 2006

Please note that this article is an archive. While every effort was made to ensure the information was accurate at the time of publication, the article has not been updated since this time. 

Last Modified: June 15, 2006