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Gestational diabetes

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Gestational diabetes mellitus (GDM) is a condition characterised by elevated blood glucose and insulin resistance that is first detected during pregnancy

  • can develop during any stage of pregnancy, but most commonly presents in the second or third trimester (1)
  • in healthy pregnancies, increased insulin resistance is a necessary physiological change that facilitates adequate carbohydrate supply for the fetus and the stimulation of fetal pancreatic insulin as an essential growth hormone, to meet the increased energy demands of pregnancy. However, in pregnant women with GDM, hyperglycaemia and resistance to insulin is overly pronounced (2)

The most common form of GDM ( approximately 80% cases) is characterised by pancreatic beta-cell dysfunction, where beta-cells are no longer able to accurately detect blood glucose concentration or to adequately control release of insulin

  • occurs following chronic insulin resistance, which is thought to occur in addition to the normal insulin resistance in pregnancy (1,2)
  • in addition, neurohormonal networks (e.g. leptin, adiponectin) along with several organ systems (e.g. pancreas, adipose, liver, muscle, gut, brain, placenta) may play a role in the pathogenesis of GDM (1,2)

GDM in the UK (3)

  • 700,000 pregnancies each year in England and Wales. Of these, 5% are complicated by hyperglycaemia (35,000), of which 12.5% have pre-existing diabetes (4,375) and 87.5% (30,625) gestational diabetes
  • GDM was defined by the National Diabetes Data Group in 1979 as any degree of hyperglycaemia at onset or first recognition during pregnancy
    • includes undiagnosed pre-existing diabetes as well as people who develop diabetes transiently as a result of pregnancy
    • in the second group, hyperglycaemia occurs when pancreatic beta cell function is insufficient to overcome the physiological insulin resistance of pregnancy induced by pregnancy hormones such as human placental lactogen and adipokines
    • individuals with a pre-disposition to insulin resistance are therefore at risk of gestational diabetes, and risk factors include ethnicity, family history, obesity and polycystic ovarian syndrome
    • prevalence rates vary widely depending on the diagnostic criteria used and populations studied. Data from the Born in Bradford Study 2007-2011 showed prevalence rates of 2% to 8·7% in white British women and 4% to 24% in south Asian women using six different criteria

Diabetes in pregnancy is associated with risks to the woman and to the developing fetus. Miscarriage, pre-eclampsia and preterm labour are more common in women with pre-existing diabetes. In addition, diabetic retinopathy can worsen rapidly during pregnancy. Stillbirth, congenital malformations, macrosomia, birth injury, perinatal mortality and postnatal adaptation problems (such as hypoglycaemia) are more common in babies born to women with pre-existing diabetes

NICE (4) suggest testing criteria for gestational diabetes as:

  • use the 2-hour 75 g oral glucose tolerance test (OGTT) to test for gestational diabetes in women with risk factors (see below)

  • offer women who have had gestational diabetes in a previous pregnancy:
    • early self-monitoring of blood glucose or
    • a 75 g 2-hour OGTT as soon as possible after booking (whether in the first or second trimester), and a further 75 g 2-hour OGTT at 24-28 weeks if the results of the first OGTT are normal

  • offer women with any of the other risk factors for gestational diabetes a 75 g 2-hour OGTT at 24-28 weeks (see below)

  • glycosuria detected by routine antenatal testing
    • be aware that glycosuria of 2+ or above on 1 occasion or of 1+ or above on 2 or more occasions detected by reagent strip testing during routine antenatal care may indicate undiagnosed gestational diabetes. If this is observed, consider further testing to exclude gestational diabetes
  • risk factors for gestational diabetes:
    • BMI above 30 kg/m2
    • previous macrosomic baby weighing 4.5 kg or above
    • previous gestational diabetes
    • family history of diabetes (first-degree relative with diabetes)
    • minority ethnic family origin with a high prevalence of diabetes

  • diagnosis of gestational diabetes
    • diagnose gestational diabetes if the woman has either:

      • a fasting plasma glucose level of 5.6mmol/litre or above or

      • a 2-hour plasma glucose level of 7.8mmol/litre or above

Before insulin was available, the perinatal mortality associated with diabetes approached 50%. Over the last 60 years, this horrific figure has been reduced to 2% in the best units. Nevertheless perinatal mortality amongst the babies of diabetics is still several times higher than amongst the general population and so continued attention must be paid to the well being of these patients through pregnancy.

At 6 weeks or more postpartum, diabetes UK suggest that a further oral glucose tolerance test should be undertaken in women diagnosed with gestational diabetes (whether or not the patient still has impaired glucose tolerance or impaired fasting glycaemia). These women, whatever the result of the oral glucose tolerance test, are at an increased risk of developing diabetes later in life.

NICE however suggest that (4)

  • women who were diagnosed with gestational diabetes should be offered lifestyle advice (including weight control, diet and exercise) and offered a fasting plasma glucose measurement (but not an oral glucose tolerance test) at the 6-week postnatal check and annually thereafter

comparison of oral hypoglycaemic agents and insulin

  • a systematic review concluded that there was no substantial maternal or neonatal outcome differences found with the use of glyburide or metformin compared with use of insulin in women with gestational diabetes (5)

The management of women with diabetes (Type 1 or Type 2) who become pregnant is described in the linked items in the menu below.

Prevention of gestational diabetes

  • US prospective cohort study (n=4275) found those with optimal control of all five modifiable risk factors (not being overweight or obese; high quality diet; regular exercise; moderate alcohol consumption; no current smoking) had a >90% lower risk of developing type 2 diabetes (6)

Presence of risk factors for gestational diabetes and subsequent development of gestational diabetes

  • if gestational diabetes
    • having risk factors for gestational diabetes is associated with worse outcomes than for women with no risk factors (7)
      • the 5-45% of women with gestational diabetes without risk factors have fewer pregnancy related complications than those with risk factors
      • women with specific risk factors (such as body mass index >30 kg/m2, family history of type 2 diabetes, or previous gestational diabetes) are more likely to require insulin

Note that a review of 229,757 births found that despite an increase in diagnosis of gestational diabetes (GDM) between the two periods, 2011-2013 and 2016-2018 (7.8% to 14.3%) there was no improvement in pregnancy related outcomes (8)

Reference:

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