There are two types of diabetes encountered in pregnancy.
On most occasions it is gestational (pregnancy induced) diabetes. This is diabetes that has its onset in pregnancy and usually resolves after delivery.
Gestational diabetes is a relatively common adverse development in pregnancy. It is now reported to occur in about 15% of pregnancies.
A few women are diabetic pre-pregnancy. They usually have insulin dependent diabetes. These women will need more insulin in pregnancy to maintain a normal range blood sugar (glucose) level (BSL). After delivery, their insulin requirements will usually go back to their pre-pregnancy level.
Background to diabetes in pregnancy
Diabetes is where there is too much glucose (sugar) in the bloodstream and consequently a pregnant woman’s BSL increases to an abnormally high level.
Glucose is an important source of energy. The hormone insulin is needed to allow glucose in the bloodstream to enter the body cells and be used for energy. Insulin is made by the pancreas gland.
During pregnancy some of the hormones produced by the placenta reduce the action of insulin. The pancreas then needs to produce extra insulin to keep her BSL in the normal range. This happens in all pregnancies. If a woman has pre-pregnancy diabetes, then her insulin requirements gradually increase as the pregnancy advances. If a woman is not diabetic pre-pregnancy, then gestational diabetes will develop if her pancreas is unable to produce enough insulin to keep her BSL in the normal range. This is a gradual process and consequently the onset is unusually before the 24th week of pregnancy. Most gestational diabetes happens by 28 weeks. I have had some patients where gestational diabetes is not apparent until the last weeks of pregnancy (with normal diabetes checking results prior).
After delivery, her BSL usually goes back to what it was pre-pregnancy. That means gestational diabetes usually resolves with delivery of her baby.
A woman with gestational diabetes is at increased risk of it happening again in subsequent pregnancies and later in life.
If a woman had diabetes pre-pregnancy, then her insulin requirements usually go back to what they were pre-pregnancy.
What are the risks of not maintaining a normal range BSL in pregnancy?
- High BSLs pre-pregnancy can cause difficulty in conceiving.
- Miscarriage and birth defects. High BSLs in early pregnancy can increase the risk of miscarriage and of birth defects, such as heart defects or defects of the brain or spine.
- Excessive birth weight. If a woman’s BSLs are high during pregnancy, extra glucose passes across the placenta to the baby. Baby will make extra insulin to allow this extra glucose to enter body cells. Consequently, sometimes baby grows excessively, which can cause problems during labour, and increased the need for an operative vaginal delivery or a Caesarean section.
- Early (preterm) birth. High BSLs may increase women’s risk of early labour and planned delivery before the due date. An earlier than 40-week delivery may be recommended because the baby is large or concerns about baby’s wellbeing.
- Respiratory distress syndrome. Baby is at increased risk of immature lungs and so newborn breathing difficulties. This can be a problem even if baby is term gestation.
- Low BSL (hypoglycaemia). After the birth, the baby may have a greater risk of low BSLs (hypoglycaemia or hypo). This is because the baby is no longer receiving extra glucose from their mother, but continues to make extra insulin, causing the baby’s BSL to drop. Severe episodes of hypoglycaemia may cause seizures in the baby. Prompt feedings and sometimes an intravenous glucose solution can return the baby’s BSL to normal.
- Obesity and type 2 diabetes later in life. Babies of mothers who have gestational diabetes have a higher risk of developing obesity and type 2 diabetes later in life.
- Untreated or poorly managed diabetes can result in a baby’s death.
- Excess amniotic fluid. This will make a pregnant woman more uncomfortable. As well there is increased risk of a ‘transverse lie’ of baby or ‘breech presentation’ and so the need for a Caesarean section delivery. There is increased risk of spontaneous rupture of membranes before labour. Excessive amniotic fluid draining rapidly with rupture if membranes increased the risk of umbilical cord prolapse.
- Intrauterine foetal growth retardation. Diabetes is associated on occasions with placental insufficiency and lack of nutrition getting to baby. That means baby is at risk of being too small and of foetal distress.
- Women with gestational diabetes also have an increased risk of developing preeclampsia.
Diagnosis and incidence of Gestational diabetes
When I started my training to be an obstetrician gestational diabetes was suspected if a pregnant woman had significant sugar in her urine (1+ or more on dipstick checking) or her baby was large for her weeks of pregnancy (‘large for dates’). She would then have an oral glucose tolerance test (OGTT) and if the result was abnormal gestational diabetes was confirmed. During the 3 days preceding the OGTT, 150 g of carbohydrate should be eaten (approximately ten 40 g slices of bread per day). As well the woman should fast for six hours prior to testing. If gestational diabetes had not been diagnosed and her baby was born with macrosomia (much larger than average size) then an OGTT was done after delivery.
The concern with this diagnosing regime was gestational diabetes was being underdiagnosed and so the Glucose Challenge Test (GCT) was introduced as routine for all pregnant women at about 26 – 28 weeks gestation. With the GCT there was no need to fast. The woman drank 50gm glucose in a flavoured drink over ten minutes and had her BSL checked 1hr later. If the result was abnormal then she had an OGTT. If the OGTT result was abnormal then gestational diabetes was diagnosed. Between 3- 8% of pregnant women were diagnosed with gestational diabetes.
There was still concern gestational diabetes was underdiagnosed with the GCT, and that about 20% of women with gestational diabetes were missed. Because of this, in 2015 the gestational diabetes checking was changed to the current regime. Now all pregnant women have an OGTT. The new pregnancy OGTT is different to the past pregnancy OGTT and to the non-pregnant OGTT. With the current pregnancy OGTT there is no need for a high carbohydrate load prior and the OGTT BSL levels for diagnosing diabetes are less than diagnostic levels for a non-pregnant patient.
It is now recommended all pregnant women (who are not already diabetic) have a 75gm two-hour OGTT at 26 to 28 weeks of pregnancy. There is no need for any diet changes before the OGTT, but the pregnant woman needs to be fasting for at least six hours prior to testing.
The pregnancy OGTT result is considered abnormal if one or more of the three BSL results is elevated. The BSL is elevated (abnormal) if…
- Fasting BSL ≥ 5.1 mmol/l
- 1 hr BSL ≥ 10.0 mmol/l
- 2 hr BSL ≥ 8.5 mmol/l
It is also recommended that all low-risk pregnant women have a random BSL level check organised at their first antenatal visit. If there are increased risk factors for diabetes, then an OGTT should be done in the first trimester of pregnancy instead of a BSL check.
Being aware that there can be diabetes problem before 26 weeks, or a woman can develop gestational diabetes in first advanced pregnancy (OGTT at 26 -28 weeks with normal results) because increased insulin demands in later pregnancy, I check a pregnant woman’s urine at each antenatal visit for glucose. If there is significant sugar in her urine (1+ or more on dipstick checking) or if in later pregnancy her baby is significantly large for her weeks of pregnancy, then I arrange for her to have an OGTT. I have diagnosed gestational diabetes even a term gestation with this checking regime.
The Australian Government reported1 1 in 7 (15%) of pregnant women had gestational diabetes in 2016–17. The incidence increased with age (26% in the 45–49-year-old age group). There was also an increased incidence in women of socioeconomic disadvantage, women born in Asia, northern Africa, and the Middle East and in aboriginal and Torres Strait Islander women.
It is reported the incidence of gestational diabetes has almost quadrupling prevalence over the last decade. Rising rates of maternal overweight and obesity, increasing maternal age and the diversity of ethnicity are key epidemiological impactors, overlaid by the 2015 changes in screening and diagnostic parameters.
Personally, I think the gestational diabetes diagnosis bar is now too low and we are labelling some women with gestational diabetes who do not have a diabetes problem. I base this conclusion on personal clinical observations where some women with borderline abnormal OGTT results have neither the build or risk factors and have very normal BSL results from the outset of BSL monitoring with minimal diet change needed. But it is much safer to have the current diagnostic criteria than the diagnostic criteria in the past when gestational diabetes was missed in some pregnant women.
Timing of gestational diabetes screening.
It is recommended gestational diabetes screening be done at 26 to 28 weeks. At this gestation, the OGTT will detect most women who develop gestational diabetes. Some women want to have the test earlier, but they do not understand the pathophysiology of gestational diabetes. The test can be done earlier but it will miss most women who develop gestational diabetes. Women can forget to have the test and get concerned they are too late for diagnosis. Gestational diabetes screening can be done at a later gestation than 28 weeks with accuracy. There will be women who have gestational diabetes with delayed diagnosis, but this is unlikely to have significant clinical impact.
Pregnancy is usually a challenge because of the increased importance of maintaining BSL readings in the normal range. I have had many women who because they have had diabetes for years have been ‘a bit slack’ in maintaining optimal BSL levels. It is essential in pregnancy for the wellbeing of baby and to minimise the risk of diabetes complications to have normal range BSL readings.
On occasions diabetes is diagnosed in the first trimester of pregnancy. This is not usually gestational diabetes, but rather the woman had undiagnosed diabetes when she conceived.
A pregnant woman is considered at high risk of gestational diabetes in these cases:
- Gestational diabetes in a previous pregnancy.
- First-degree relative with diabetes.
- Previous pregnancy history of macrosomia (>4.5 kg baby).
- Previous pregnancy with unexplained stillbirth.
- History of PCOS.
- Morbid obesity BMI ≥ 35.
- Maternal age > 40 years old.
- On oral corticosteroids.
- Asian, Aboriginal, Pacific Islander, Maori, Middle Eastern, African ethnicity.
- Has sugar in urine at antenatal visit.
- Has too much amniotic fluid (hydramnios).
What will be the impact of diabetes on your antenatal care and delivery?
- Endocrinologist referral. An endocrinologist is doctor who specialised in the management of diabetes. If you have pre-pregnancy diabetes it is highly likely you are under the care of an endocrinologist. If not, I will arrange this. If you develop gestational diabetes, I will arrange for you to see an endocrinologist.
- The endocrinologist will arrange for you to see a dietician and commence home glucose monitoring.
- Your focus is on maintaining your BSLs in optimal range by a healthy diet, exercise, and insulin (if needed).
- Your blood sugar crosses the placenta and so your BSL is reflected in your baby’s BSL. Your baby’s wellbeing is at considerable risk if your BSL is too high or too low for a significant period. Your insulin does not cross the placenta to your baby.
- If exercise and diet are no sufficient for you to maintain a normal range BSL then you will need insulin. How much insulin you need is a marker of the severity of your diabetes. The important thing in not how much insulin you need but that you maintain a normal range BSL. I recently had a patient requiring 170 units of insulin per day to maintain a normal range BSL. She was very diligent in maintaining a normal range BSL and she had a successful pregnancy outcome of a normal sized baby.
- If you are on insulin to maintain optimum BSLs and you notice your insulin requirements decreasing, then please advise me immediately. It may be that there is placental insufficiency, which increases the risk to your baby’s wellbeing.
- I will be monitoring your wellbeing and your baby’s growth and wellbeing carefully in the pregnancy.
- Delivery is advised at 38 to 40 weeks because of concern about the increased risk of placental insufficiency if you go overdue. That means an increased likelihood of induction of labour.
- There will be close monitoring in labour of your baby’s wellbeing and of your BSL.
- If you are having an elective Caesarean section, you will need to fast for six hours prior. This will impact your diabetes management and can result in you having a low BSL. You may need to be admitted earlier than usually is the case to make sure your BSL is stable. Your insulin dose pre-Caesarean section will need to be adjusted with consideration that you will be fasting.
- Your baby will be admitted to the Special Care Nursery after delivery if you need more than 15 units of insulin per day, until the paediatrician is confident that your baby’s BSL is optimal and stable.
- You will need to see the endocrinologist at about six weeks after delivery to check your wellbeing and to discuss how you can minimise the likelihood of diabetes in the future.
But please do not be anxious. I have successfully managed many hundreds of pregnant women with diabetes, including many who were diabetic pre-pregnancy and on high doses of insulin at their first antenatal visits. With proper treatment and diligence in maintaining a normal range BSL I am confident all will go well in your pregnancy despite having diabetes.
What can you do pre-pregnancy to minimise the likelihood of gestational diabetes?
These is increasing diabetes in the community. This has been attributed to unhealthy eating habits, lack of exercise and increasing obesity by an increasing number of Australians. The best ways you can help minimise the likelihood of having a gestational diabetes problem is…
- Having a healthy diet, including reducing your sugar intake.
- Start an exercise program to complement your lifestyle.
- Maintaining a healthy BMI (body mass index). You can check your current BMI at Australian Government Department of Health website page BMI Calculator. 2
The recommended guidelines are…
|Less than 18.5||Underweight|
|18.5–24.9||Healthy weight range|
|30 and over||Obese|
|40 and over||Morbidly obese|