How gestational diabetes can affect your baby

Gestational diabetes affects one in 20 pregnant women and can seriously compromise your health and the health of your unborn baby, explains Dr Emma Parry.

Pregnancy is a challenge for both body and soul. Managing the rapidly changing energy requirements of pregnancy can be a balancing act of diet, hormones, chemicals and body mass index (BMI).

For some women things can get out of kilter and that's why pregnant women undergo regular checks, including blood pressure tests and blood tests, throughout pregnancy. One of those checks is a blood test after a sweet drink when you're about 28 weeks pregnant and, if you're unlucky, the result will lead to a diagnosis of gestational diabetes.

Increased glucose (sugar) is needed for the developing baby and the body has a number of mechanisms to increase the glucose in the bloodstream. After a meal the amount of glucose naturally increases as it is absorbed from the gastro-intestinal tract. This is transported in the blood to tissues, however there is more than is needed straight away after a meal so the extra glucose is stored for later.

This is where the hormone insulin comes in. Insulin is released from the pancreas (just under the liver in the top of the abdomen) when there is excess glucose in the blood stream. It helps the glucose to be moved into storage for later use. In pregnancy, as the amount of glucose increases, more insulin is required to keep glucose levels on an even keel. In some women the pancreas has a job keeping up and the glucose level gets very high in the bloodstream. When a threshold is reached this is called gestational diabetes mellitus (GDM).

Diagnosing gestational diabetes

Factors that increase the risk of gestational diabetes include increased BMI, having a close relative with diabetes, being older, having had more babies and previous GDM during pregnancy.

In New Zealand there is currently a two-stage process for diagnosing GDM. At 28 weeks women are offered a screening test called a Polycose. The test is done at 28 weeks as, prior to this, many women can cope with the extra pregnancy insulin requirements, but at 28 weeks the body starts to find it harder. In some cases a woman will not have an abnormal result at 28 weeks but a clinical change, such as a scan showing a large baby, may prompt a repeat test later on in the pregnancy.

Your Lead Maternity Carer (LMC) should send you to a screening lab to have the test taken. Most labs don't require you to make an appointment but it's best to check first.

This test involves drinking a standard sugar drink and then having a blood test for glucose one hour later. If the level is above a cut-off point the mum-to-be is referred for a diagnostic test - a Glucose Tolerance Test (GTT). This is more complicated. You'll need to starve beforehand (not always easy if you faint a lot!) and turn up for a blood test. You then have a standard sugar drink and will be asked to stay at the lab for the next two hours to minimise exercise (which can affect glucose levels) and have a further blood test at one hour and two hours after the sugar drink. If the threshold is reached you will be told you have gestational diabetes.

The threshold for diagnosis currently used in New Zealand means that about 5% of women have GDM, that's about 3000 women a year, given the birth rate has hovered around 60,000 for the past few years. So it is relatively common and in the vast majority of cases the glucose levels return to normal after the birth of the baby.

So why bother to diagnose it? Surely more glucose is better?

How gestational diabetes affects the baby

The main concern with GDM is the effect on the baby. Glucose easily crosses the placenta into the baby's bloodstream and this high level has several detrimental effects. The increased glucose leads to hormonal changes that mean the baby grows more than normal and will have increased fat stores. At birth this can lead to difficulty during delivery and a greater chance of intervention and complications for the mother, such as caesarean section or haemorrhaging after the birth.

Gestational diabetes is also associated with polyhydramnios (excess fluid around the baby) which can lead to early labour and rupture of the membranes and the baby being in the wrong position at the time labour starts. In the last couple of months of pregnancy babies of GDM mothers are at higher risk of stillbirth. This rate is increased when the GDM is not recognised or is not well controlled and treated.

After birth babies are at increased risk of breathing problems, jaundice and having low blood sugar levels. Better control before birth also helps reduce these problems.

Treatment of gestational diabetes

Women who have been diagnosed with gestational diabetes mellitus will be referred by their LMCs to the local pregnancy diabetes clinic for review.  The clinic usually has a multi-disciplinary team approach and the mother-to-be may see an obstetrician, diabetes doctor and/or dietitian. The first option is to look at diet. Foods which release a quick hit of glucose are out. And that means food such as chocolate bars and fizzy drinks. Slow release sugars are in, such as brown bread (all those husks to break down), and foods which are low Glycaemic Index. To check this is working the mum-to-be will start to monitor her own glucose levels at home using a finger prick test. She keeps a record and then talks to the team of professionals about the results.

Many women need more than a change in diet to manage their GDM. The next treatment maybe a tablet to lower the glucose levels (metformin) or insulin treatment. Insulin treatment is a bit more complicated and the mum will get lots of support to ensure she's happy doing this. Insulin is in liquid form and cannot be taken by mouth as it will not be absorbed. Instead, it is given as a subcutaneous injection. This means it is given just under the skin and is therefore very easy to administer. It requires only a very small needle.

I find it amazing how well women cope when they need to start insulin. It is usually needed three to four times a day, though if used in conjunction with tablets, it can be reduced to only once a day.

The mother-to-be needs to stay on the restricted diet as well. If she has a BMI in the overweight or obese range she may be encouraged not to gain any further weight in the pregnancy or even carefully lose weight. Throughout this phase she will have regular check-ups including ultrasound scans of the baby to check the growth. Women with GDM have a higher chance of developing pre-eclampsia (high blood pressure in pregnancy) and regular blood pressure checks will be carried out. Some women will need to be admitted to hospital before the birth to help control their sugar levels or because they have a complication such as pre-eclampsia which needs closer monitoring.

It is likely an induction of labour will be recommended at the due date or earlier to avoid complications for the baby.

After the birth the baby will have careful checks which may include testing the baby's glucose level. The baby may have a low glucose level because he's been used to lots of glucose in the bloodstream and has increased his own insulin supply. After birth the glucose levels are normal as there is no glucose coming from the mum's bloodstream, but there are still high levels of insulin which drive the glucose from the blood to the stores. A very low glucose level is dangerous for the baby and extra feeds may be needed.

Glucose levels most often return to normal after the birth. However, a repeat GTT is usually recommended at six weeks after the birth as some women will have an intermediate condition called impaired glucose tolerance (IGT) where repeat screening for diabetes throughout her life is recommended. The new mother can return to her usual diet after pregnancy unless her LMC or diabetes team advise otherwise. However it is worth noting that the low GI diet used to treat GDM is actually a very healthy way to eat. This might the beginning of a whole new you!

How can I avoid gestational diabetes?

Many factors which increase the risk of GDM cannot be changed. These include ethnicity and family history. However, if you know you are at increased risk it is worth considering some changes before and during pregnancy. If your BMI is increased before you get pregnant, try to lose some weight.

Choose a diet that advocates a low GI approach so that if you do have GDM in pregnancy, you are already on the correct food and the GDM will not be as difficult to treat. Exercise is important as it uses up calories and helps to even out the highs and lows of glucose metabolism.

Will it happen in my next pregnancy?

If you had GDM in your first pregnancy there is a much higher chance in your next pregnancy. Often the Polycose test or GTT will be done earlier than 28 weeks and may be repeated more than once.

Dr Emma Parry is a specialist obstetrician and gynaecologist, a sub-specialist in Maternal-Foetal Medicine, Clinical Director of MFM at Auckland Hospital and a spokesperson for the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). She's involved in training and teaching for both medical and midwifery colleagues and has used her skills in Bhutan in the Himalayas, where she helped establish a high-risk maternity service.