There is a separate article on Diabetes in Pregnancy.
Gestational diabetes mellitus (GDM) is any degree of glucose intolerance with its onset (or first diagnosis) during pregnancy and usually resolving shortly after delivery. There are several different versions of the diagnostic criteria, but the definition by the World Health Organisation (WHO) is the most widely used. Either of the following:
- Fasting venous plasma glucose ≥7 mmol/L (ie in diabetic range - don't rely on fasting plasma glucose too exclude GDM - do a 2 hr glucose tolerance test if fasting glucose is below this).
- Plasma glucose ≥7.8 mmol/L two hours after a 75g glucose load as part of the oral glucose tolerance test (OGTT). This group includes those with diabetes and impaired glucose tolerance.
Pregnancy hormones decrease fasting glucose levels, increase fat deposition, delay gastric emptying and increase appetite. However, over the course of pregnancy, postprandial glucose concentrations increase as insulin resistance increases - hence, the perception of pregnancy as a diabetogenic state. This is normally countered by an increased production of insulin but in women with GDM there is an insufficient compensatory rise.
Many of the problems associated with GDM are common to established diabetes in pregnancy - hyperglycaemia promotes large-for-dates babies and is associated with adverse fetal and maternal outcomes. There is no agreement on the glycaemic threshold for these adverse outcomes - indeed, large studies have indicated a strong, continuous association of maternal glucose levels (below those diagnostic of diabetes) with increased birth weight, and significant associations with secondary outcomes such as preterm labour, shoulder dystocia, birth injury, intensive neonatal care requirement, hyperbilirubinaemia, and preeclampsia.
It increases risk of developing diabetes later in life by at least seven-fold, so is frequently considered a pre-diabetic state, with increased cardiovascular risk. This increases GDM's significance beyond solely an obstetric issue.
GDM is a growing health concern in many parts of the world - it occurs in 2-5% pregnancies but figures vary considerably depending upon the criteria used. Only 10% of these patients would be diabetic if it wasn't for the pregnancy effects on glucose (ie 10% were diabetic but coincidentally diagnosed when pregnant).
GDM is more likely with:
- Increasing age
- Certain ethnic groups (Asian, African Americans, Hispanic/Latino Americans and Pima Indians)
- High BMI before pregnancy (three-fold risk for obese women compared to non-obese women)
- Smoking - it doubles the risk of GDM
- Change in weight between pregnancies - an inter-pregnancy gain of more than three units (of BMI) doubles the risk of GDM 
- Short interval between pregnancies
- Previous unexplained stillbirth
- Previous macrosomia
- Family history of type 2 diabetes or GDM - more relevant in nulliparous than parous women
- Physical activity, especially vigorous activity before pregnancy and at least light-to-moderate activity during pregnancy may reduce risk for abnormal glucose tolerance.
- Bariatric surgery reduces the future risk of developing GDM in obese women. 
GDM is usually asymptomatic but has serious consequences that can be reduced by treatment, making it a candidate for screening.
- BMI >30
- Previous macrosomic baby ≥4.5 kg or above
- Previous GDM
- First-degree relative with diabetes
- Family origin with a high prevalence of diabetes (South Asian, black Caribbean and Middle Eastern)
- Where a woman has had previous GDM, she should be offered early self-monitoring of blood glucose or a two-hour 75 g OGTT at 16-18 weeks, followed by a repeat OGTT at 28 weeks if the first test is normal
- Other risk factors should prompt an OGTT at 24-28 weeks.
- Screening for GDM should not be undertaken using fasting plasma glucose, random blood glucose, glucose challenge test or urinalysis for glucose. Whilst we routinely dip urine at every antenatal visit, the detection of glucosuria is not a sufficiently good screening tool for GDM and may delay diagnosis, adversely affecting outcome.
Timing of diagnosis:
- GDM is rare before 20 weeks, and early diagnosis of GDM is associated with poor maternal and fetal outcome. This probably reflects earlier presentation of the more severe cases or pre-existing but unrecognised diabetes. Those with pregestational diabetes are at much higher risk of having babies with a serious birth defect than those who develop diabetes in the second and third trimester.
- Glucose tolerance changes with the duration of the pregnancy so that the gestation at which the diagnosis was made should be recorded and, if made in the third trimester, there should be some caution about the clinical implications of impaired glucose tolerance (IGT).
Treatment of GDM and good glycaemic control reduces serious perinatal morbidity and may also improve the woman's health-related quality of life.
It is often controversial as to when GDM requires treatment. A recent study showed that the treatment (dietary intervention, self-monitoring of blood glucose, and insulin therapy, if deemed necessary) of mild GDM (defined as positive OGTT but fasting glucose<5.3 mmol/L) did reduce the risks of fetal overgrowth, shoulder dystocia, Caesarean delivery, and hypertensive disorders but not a composite primary outcome (based upon stillbirth or perinatal death and neonatal complications, including hyperbilirubinaemia, hypoglycaemia, hyperinsulinaemia, and birth trauma).
Women should receive routine antenatal care but in addition:
- Women are usually taught how to monitor their blood sugars, at least daily (dependent on treatment) and educated regarding individualised target levels. In general, women should aim for fasting blood glucose of between 3.5 and 5.9 mmol/L and one-hour postprandial blood glucose below 7.8 mmol/L.
- Urinalysis (looking for protein) and blood pressure checks should be performed at antenatal appointments, as women with GDM are at higher risk of hypertensive disorders.
- Ultrasound should be performed monthly to assess fetal growth and amniotic fluid volume from 28 weeks. Macrosomia is usually taken as dimensions above the 95th centile for that period of gestation. Measurement of abdominal circumference of the baby can exclude macrosomia and reduce the need for insulin without impairing outcome.
- Non-drug treatment:
- Body weight - weight loss should be aimed for with women with a BMI >27.
- Diet - all women with GDM should receive dietary advice from a specialist dietician - food choices should reflect the nutritional demands of pregnancy and concentrate on the need for micronutrient-rich food.
- Physical activity - encourage at least 30 minutes' physical activity per day, sufficient to induce slight breathlessness.
- Hypoglycaemic therapy should be considered where:
- Lifestyle adjustments fail to maintain blood glucose targets over 1-2 weeks
- Ultrasound at diagnosis shows incipient fetal macrosomia (abdominal circumference >70th percentile).
- Where hypoglycaemic therapy is required:
- Current evidence base does not suggest a significant difference between the use of oral hypoglycaemic agents and insulin in women with GDM, both for maternal glycaemic control, rates of Caesarean delivery and neonatal outcomes (such as infant birth weight, neonatal hypoglycaemia, and congenital anomalies).
- Insulins are widely used in pregnancy and generally accepted as safe. There is some evidence of improved control with a basal bolus regimen. Mothers receiving insulin therapy and those in regular contact with them should be instructed on the recognition, management and treatment of hypoglycaemia.
- Metformin is widely used in the UK for the management of diabetes in pregnancy and lactation. It appears both effective and safe, despite SPC advice that it should be avoided when planning pregnancy and during pregnancy. Similarly, glibenclamide's SPC advises that it is contra-indicated in pregnancy, despite evidence for its effectiveness and safety. Thus, informed consent should be obtained and documented prior to the use of both these drugs in GDM.
- Hypoglycaemic therapy should be considered where:
- GDM is a risk factor for Caesarean delivery (due to the risk of macrosomia and dystocia). The place and mode of delivery should depend on the state of health of mother and fetus.
- NICE guidelines suggest offering women with GDM (as for those with established diabetes) induction of labour (or Caesarean section) from 38 weeks where the baby has grown normally. Where women opt to wait for spontaneous labour, they should be offered weekly tests for fetal well-being from 38 weeks.
- During delivery, blood glucose should be measured hourly (half hourly if a general anaesthetic is used) and maintained at between 4 and 7 mmol/L.
- Babies should be encouraged to feed as soon after birth as possible (within 30 minutes) and every 2-3 hours thereafter. Blood glucose should be tested within 2-4 hours of birth or if there are signs of hypoglycaemia. Infants should not be discharged within 24 hours of birth, until feeding well and maintaining their blood glucose levels (>2 mmol/L pre-feed).
- Insulin and other hypoglycaemics are usually stopped immediately following delivery.
- The mother's blood glucose should be checked prior to discharge to the community. Fasting blood glucose is usually checked 6 weeks postpartum. Where this is diagnostic doubt, an OGTT should be pursued at this stage as if diagnosing diabetes mellitus in a patient who had never been pregnant.
- Counselling regarding the increased risk of diabetes and recurrence of gestational diabetes in subsequent pregnancies. There is some evidence that progression to type 2 diabetes can be reduced by regular physical activity and avoiding obesity.
- Women who have had GDM should be advised to have annual fasting blood glucose tests.
The risk of perinatal mortality is not increased but there are
- Increased perinatal risks of:
- Shoulder dystocia
- Birth injuries such as bone fractures and nerve palsies
- Long-term adverse health outcomes in infants born to mothers with gestational diabetes include:
- Sustained impairment of glucose tolerance
- Subsequent obesity (although not when adjusted for size)
- Impaired intellectual achievement
For the women themselves, gestational diabetes is a strong risk factor for diabetes and metabolic syndrome. Undoubtedly, interventions (diet, lifestyle, medication) that could help prevent or delay the onset of type 2 diabetes in these women would have an important effect on their long-term health. However the effectiveness of such interventions remains largely untested in clinical trials to date.
- The perinatal risks to mother and baby are similar to those with known diabetes, mainly relating to the problems of a large baby.
- Most women will apparently recover after the pregnancy but with a 2 in 3 chance of recurrence in a future pregnancy.
- The highest fasting glucose level during pregnancy, followed by the severity of glucose intolerance, and earlier gestational diabetes are the best predictors for postpartum diabetes. IGT in the first few months after delivery is associated with a high risk of diabetes in the near future.
- Repeated pregnancy, particularly close together, does appear to increase the risk of developing diabetes (whereas combined oral contraceptives and hormone replacement therapy do not).
- Children whose mothers had GDM are more likely to be obese but this does not necessarily imply a genetic or intrauterine effect. The parents are more likely to be overweight too and a shared environment may lead to similar attitudes and behaviours towards food.
Advice after gestational diabetes
Having had GDM, you are at significantly increased risk of developing diabetes and so:
- Achieve and maintain a satisfactory BMI.
- Take regular exercise.
- Do not smoke.
- Do not have pregnancies in rapid succession.
- Make sure you attend your six-week postpartum check and have a fasting blood glucose test taken.
- Have annual fasting blood glucose tests.
See separate article Prevention of Type 2 Diabetes.
Further reading & references
- Moore TR, Warshak C; Diabetes Mellitus and Pregnancy. eMedicine, May 2009.
- Reece EA, Leguizamon G, Wiznitzer A; Gestational diabetes: the need for a common ground. Lancet. 2009 May 23;373(9677):1789-97.
- Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia, World Health Organization/International Diabetes Federation, 2006
- Diabetes in Pregnancy Information Leaflet, Confidential Enquiry into Maternal and Child Health et al (2006); Important information for General Practitioners and the Primary Care Team
- Metzger BE, Lowe LP, Dyer AR, et al; Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. 2008 May 8;358(19):1991-2002.
- Bellamy L, Casas JP, Hingorani AD, et al; Type 2 diabetes mellitus after gestational diabetes: a systematic review and meta-analysis. Lancet. 2009 May 23;373(9677):1773-9.
- Nohira T, Kim S, Nakai H, et al; Recurrence of gestational diabetes mellitus: rates and risk factors from initial GDM and one abnormal GTT value. Diabetes Res Clin Pract. 2006 Jan;71(1):75-81. Epub 2005 Jul 6.
- England LJ, Levine RJ, Qian C, et al; Glucose tolerance and risk of gestational diabetes mellitus in nulliparous women who smoke during pregnancy. Am J Epidemiol. 2004 Dec 15;160(12):1205-13.
- Villamor E, Cnattingius S; Interpregnancy weight change and risk of adverse pregnancy outcomes: a population-based study. Lancet. 2006 Sep 30;368(9542):1164-70.
- Retnakaran R, Connelly PW, Sermer M, et al; The impact of family history of diabetes on risk factors for gestational diabetes. Clin Endocrinol (Oxf). 2007 Jul 3;.
- Oken E, Ning Y, Rifas-Shiman SL, et al; Associations of physical activity and inactivity before and during pregnancy with glucose tolerance. Obstet Gynecol. 2006 Nov;108(5):1200-7.
- Maggard MA, Yermilov I, Li Z, et al; Pregnancy and fertility following bariatric surgery: a systematic review. JAMA. 2008 Nov 19;300(19):2286-96.
- Crowther CA, Hiller JE, Moss JR, et al; Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. N Engl J Med. 2005 Jun 16;352(24):2477-86. Epub 2005 Jun 12.
- Diabetes in pregnancy, NICE Clinical Guideline (March 2008)
- Care recommendation - pregnancy and diabetes, Diabetes UK
- Barahona MJ, Sucunza N, Garcia-Patterson A, et al; Period of gestational diabetes mellitus diagnosis and maternal and fetal morbidity. Acta Obstet Gynecol Scand. 2005 Jul;84(7):622-7.
- Landon MB, Spong CY, Thom E, et al; A multicenter, randomized trial of treatment for mild gestational diabetes. N Engl J Med. 2009 Oct 1;361(14):1339-48.
- Nicholson W, Bolen S, Witkop CT, et al; Benefits and risks of oral diabetes agents compared with insulin in women with gestational diabetes: a systematic review. Obstet Gynecol. 2009 Jan;113(1):193-205.
- Kjos SL; After pregnancy complicated by diabetes: postpartum care and education. Obstet Gynecol Clin North Am. 2007 Jun;34(2):335-49.
- No authors listed; Gestational diabetes mellitus. Diabetes Care. 2003 Jan;26 Suppl 1:S103-5.
- Lauenborg J, Mathiesen E, Hansen T, et al; The prevalence of the metabolic syndrome in a danish population of women with previous gestational diabetes mellitus is three-fold higher than in the general population. J Clin Endocrinol Metab. 2005 Jul;90(7):4004-10. Epub 2005 Apr 19.
- Schaefer-Graf UM, Buchanan TA, Xiang AH, et al; Clinical predictors for a high risk for the development of diabetes mellitus in the early puerperium in women with recent gestational diabetes mellitus. Am J Obstet Gynecol. 2002 Apr;186(4):751-6.
- Buchanan TA, Kjos SL; Gestational diabetes: risk or myth? J Clin Endocrinol Metab. 1999 Jun;84(6):1854-7.
- Kjos SL, Peters RK, Xiang A, et al; Hormonal choices after gestational diabetes. Subsequent pregnancy, contraception, and hormone replacement. Diabetes Care. 1998 Aug;21 Suppl 2:B50-7.
- Schaefer-Graf UM, Pawliczak J, Passow D, et al; Birth weight and parental BMI predict overweight in children from mothers with gestational diabetes. Diabetes Care. 2005 Jul;28(7):1745-50.
|Original Author: Dr Chloe Borton||Current Version: Dr Hayley Willacy|
|Last Checked: 20/04/2011||Document ID: 2192 Version: 23||© EMIS|
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