Key learning points:
- High-risk mothers should be tested for gestational diabetes at 24-28 weeks gestation with a two-hour oral glucose tolerance test (OGTT)
- Management of gestational diabetes during pregnancy has been updated – new National Institute for Health and Care Excellence (NICE) guidance was issued in 2015.
The prevalence of gestational diabetes is increasing due to the obesity epidemic and increasing maternal age, and is causing a significant burden on both primary and secondary care with up to 5% of pregnancies affected (1,2).
Gestational diabetes is a significant complication in pregnancy, which can lead to delivery problems due to large babies (macrosomia), neonatal hypoglycaemia and maternal pre-eclampsia.
It is important for primary care providers, including practice nurses, to be up-to-date with current diagnostic criteria, treatment and management of these women to reduce adverse outcomes. In addition, women who have gestational diabetes will have a 7% lifetime risk of developing type 2 diabetes in the future, as pregnancy unmasks susceptibilities to insulin resistance (3).
Early identification and careful follow-ups of women with gestational diabetes can help to modify preventable risks factors and reduce their risk of type 2 diabetes and its long-term complications. The diagnosis criteria for gestational diabetes is different from ordinary diabetes and those mothers with positive glycosuria urine dip-stick tests and in high-risk groups should be formally tested.
DIAGNOSIS AND PREVALENCE
Gestational diabetes is defined as “glucose intolerance with onset or first recognition during pregnancy that resolves after childbirth” (4).
This group tends to include true gestational diabetes and women who had probable pre-existing type 2 diabetes only identified during antenatal screening. In recent years these distinct categories have tried to be separated (5) and those identified in the second and third trimesters, where the effect of pregnancy-related insulin resistance is greater, are considered to have true gestational diabetes.
The diagnostic criteria for gestational diabetes has been updated and glycaemic levels lowered due to evidence from the Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) study, which showed increased rates of adverse outcomes. These included babies that were large for gestational age, cord c-peptide (marker for fetal insulin) and new-born babies with body fat above 90th centile (6).
The International Association of Diabetes Pregnancy Study Groups (IADPSG) used this data to standardise a diagnostic criteria for gestational diabetes, which has lowered the glucose threshold for diagnosis and thus increased the prevalence of gestational diabetes to 16% (7).
NICE updated its guideline Diabetes in pregnancy: management of diabetes and its complications from preconception to postnatal period in February 2015 and this article is based upon its recommended advice (8).
This article discusses identification and management of gestational diabetes during pregnancy and should not be used for patients with pre-existing diabetes prior to pregnancy. The key message is that practice nurses and health care assistants should be: aware of the diagnostic criteria, formally test high-risk groups and patients with positive glycosuria urine stick tests.
Pregnancy and pregnancy plus obesity place a greater load on the mother, and her pancreas; the higher levels of maternal blood glucose result in potential harm to her baby. The detailed mechanism underlying this is explained:
- Pregnancy causes releases of placental hormones such as progesterone, tumour necrosis factor-alpha and human placental growth hormone, which during the second and third trimester cause insulin resistance.
- In women with gestational diabetes there is a greater insulin resistance and impairment of compensatory mechanisms to increase insulin secretion and therefore diabetes develops (9).
- There is a small subset of gestational diabetic women who develop diabetes from autoantibodies to islet cells in the pancreas and they are at increased risk of autoimmune mediated diabetes (10).
Most adverse outcomes to mother and baby are secondary to maternal hyperglycaemia and therefore control of blood glucose during pregnancy is pivotal. Fetal exposure to maternal hyperglycaemia causes hyperplasia of fetal pancreatic cells, once born they are at increased risk of significant hyperinsulinaemia and prolonged hypoglycaemia.
Additionally there is an increase in adipose tissue around the chest, shoulder and abdominal regions, which are insulin-sensitive and cause complications such as shoulder dystocia, birth trauma and perinatal death.
RISK FACTORS FOR GESTATIONAL DIABETES
It is important to identify women at risk of gestational diabetes early in order to prevent consequences of uncontrolled hyperglycaemia. Women who are seen in the community who have one or more of these risk factors (see Table 1) should be offered diabetic testing at 24-28 weeks gestation with a two-hour oral glucose tolerance test (OGTT).
(Either early self-monitoring of blood glucose to start on first booking) or a 75g 2-hour OGTT as soon as possible after booking and a further 75g 2-hour OGTT at 24-28 weeks (if the results of the first OGTT are normal).
Increasing maternal age may also be a risk factor (11,12). Women of Pakistani, Indian or Sri Lankan or of North African ethnicity are at greater risk than those of European ethnicity. Women from sub-Saharan Africa at lower risk (13).
It is common for pregnant women to have repeated urine dipsticks in the community and in outpatient antenatal clinics and therefore it is important to be aware that glycosuria is also a sign of potentially undiagnosed diabetes. Women should be considered for testing for gestational diabetes if they have tested positive for:
- Glycosuria of 2+ or above on one occasion.
- Glycosuria of 1+ or above on two occasions.
DIAGNOSIS OF GESTATIONAL DIABETES
Prior to screening for gestational diabetes it is essential to inform and council women on the potential outcomes of the test. Gestational diabetes is often managed with diet and exercise alone but those that do not have sufficient control of blood glucose will be advised to take glucose-lowering agents or insulin therapy. This is vital for reducing complications of hyperglycaemia such as delivery problems due to large babies, which include shoulder dystocia. As women with gestational diabetes are at risk for problems during pregnancy and labour, increased monitoring is required that may lead to increased interventions during compared to pregnancies not complicated by gestational diabetes.
The current diagnostic criteria for gestational diabetes is as follows (if a patient has either):
- A fasting plasma glucose of 5.6mmol/l or above.
- A two-hour plasma glucose level of 7.8mmol/l or above after a 75g oral glucose tolerance test (OGTT).
After being diagnosed with gestational diabetes a review in a joint diabetic and antenatal clinic within one week should be offered and the primary healthcare team should be informed.
MANAGEMENT OF GESTATIONAL DIABETES
Information is crucial to help women understand the importance of good glucose control for her health and the health of her baby. Good glucose control throughout pregnancy will reduce the risk of fetal macrosomia, trauma during birth, induction of labour and/or caesarean section, neonatal hypoglycaemia and perinatal death (14).
Alongside strict monitoring of blood glucose with input from an endocrinologist, women will also be offered an increased antenatal care package including more frequent ultrasound scans to assess the size and well-being of the baby and liquor volume.
Blood glucose monitoring kits should be given to women and self-monitoring should be taught with repeat prescriptions for necessary equipment and medications e.g. needles, sharps bins.
The main form of treatment is blood glucose control and the initial treatment offered is dependant on the results of the OGTT (see Table 2).
Simple lifestyle changes are enough in many women to control their glucose level and all women should be referred to a dietician to review their diet and provide information on low glycaemic index foods. In addition to this, exercise has been shown to stabilise post prandial blood glucose and reduce the need for insulin.
Metformin is a well-established drug that reduces the amount of glucose created in the liver and makes the body more sensitive to insulin. In detail, metformin is a biguanide oral antidiabetic medication and it works by suppressing hepatic gluconeogenesis, increasing insulin sensitivity and decreasing the absorption of glucose from the gastrointestinal tract. This glucose-lowering therapy should be offered first to women who have uncontrolled hyperglycaemia unless contraindicated.
When metformin was compared to insulin it was found to have no significant differences between outcomes such as shoulder dystocia and infants born large for gestational age. Additionally the administration is considered much easier and preferred compared to insulin.
Glibenclamide is also a well-established medicine that drives the pancreas to produce more insulin. In more detail, glibenclamide is a sulphonylurea and acts by stimulating insulin release from the beta-cells in the pancreas. There are no significant differences between the use of insulin and metformin compared to glibenclamide for the prevention of shoulder dystocia or large for gestational age, however there is no long-term data for the effects of glibenclamide in pregnancy and therefore metformin and insulin are used preferentially.
When oral medications don’t control gestational diabetes, insulin is needed. Exogenous insulin is used in conjunction with diet, exercise and metformin if required for glucose control. Insulins that are used preferentially are isophane/detemir insulin and lispro/aspart insulin as long-acting and short-acting insulin respectively. It is important to warn women of the effects and prevention of hypoglycaemic events. Users must also be made aware of DVLA guidelines with insulin use.
Blood glucose aims
Women should record their blood sugar monitoring daily. If they have repeatedly high blood glucose they should seek medical advice in order to change or increase their current management. Those on glibenclamide and insulin should maintain a blood glucose above 4mmol/l in order to prevent problematic hypoglycaemias.
DELIVERY AND POSTPARTUM
At 36 weeks, women with gestational diabetes will have an obstetric/hospital antenatal clinic to discuss the timing, mode and management of birth including the analgesia and management of blood glucose during labour.
Advice regarding the postpartum period is vital to ensure women are informed of the interventions and monitoring that may be necessary. Babies born to women with diabetes will need to have their blood glucose level tested at two-four hours post delivery to ensure they are not hypoglycaemic.
Women with gestational diabetes should discontinue their blood glucose-lowering therapy immediately after birth as they are at risk of hypoglycaemia at this time.
They should have their blood glucose measured to exclude persisting hyperglycaemia prior to being transferred to community care and reminded of the symptoms of hyperglycaemia should they reoccur once at home.
On-going community care
Community follow-up is essential to provide on-going modifications of risk factors. At six-13 weeks post-partum fasting plasma glucose should be offered to exclude on-going diabetes. After this, a HbA1c test should be done yearly to test for emerging type 2 diabetes.
CHALLENGES FOR THE FUTURE
There is likely to be an ongoing debate regarding the ideal diagnostic criteria for gestational diabetes as previous criteria was not evidence based.
However, with new NICE guidance based on the evidence from the HAPO study it will be interesting to see whether we have significant improvements in perinatal morbidity with reduction in rates of shoulder dystocia, large for gestational age and perinatal mortality.
With a lowered threshold for the diagnosis of gestational diabetes and the subsequent overnight increase in prevalence of gestational diabetes to affect 16% of pregnancies, it will be vital for community teams to become involved in the diabetic management of this increased patient load.
The change in recent diagnostic criteria to lower the glycaemic threshold for diagnosis has caused an epidemic overnight and the management and treatment of these patients is vital to prevent adverse outcomes. Practice nurses and health care assistants should know about this condition, and ensure that high-risk groups and those with glycosuria are formally tested.
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