Diabetes in Pregnancy and Gestational Diabetes

Gestational Diabetes

Any degree of glucose intolerance with its onset (or first diagnosis) during pregnancy, and usually resolving after delivery.

Diabetes in Pregnancy

Pregnancy in which the mother has pre-existing diabetes mellitus.


  • Diabetes is the most common pre-existing medical disorder complicating pregnancy- and can affect both the mother and foetus.
  • Gestational diabetes occurs in around 2-5% of pregnancies
    • Around 10% of these patients would have had some degree of pre-existing diabetes
    • The majority of complications associated with diabetes in pregnancy are found in gestational (rather than pre-existing) diabetes

Risks of Diabetes in Pregnancy

  • Maternal
    • Increased insulin resistance
    • Hypoglycaemia
    • Infection
    • Ketoacidosis
    • Deterioration of retinopathy, nephropathy (proteinuria)
    • Pre-eclampsia
      • For every 1% increment rise in HbA1c- there is a 60% increased risk of pre-eclampsia
    • Miscarriage
    • Pre-term labour
    • Shoulder dystocia
    • Assisted delivery
    • Polyhydramnios
  • Foetal
    • Congenital abnormalities
      • At conception an HbA1c <8% – 5% risk; >10% – 25% risk
    • Increased neonatal/perinatal mortality
    • Macrosomia
    • Late still birth
    • Preterm delivery
    • Polycythaemia
    • Neonatal hypoglycaemia (beta cell hyperplasia)
    • Respiratory distress syndrome (delay in surfactant production)
    • Jaundice
    • Shoulder dystocia
    • Hypomagnesaemia/hypocalcaemia


  • At around 20-24 weeks gestation, the placenta releases hormones such as human placental lactogen, glucagon and cortisol- all of which counteract the effects of insulin
    • Normally, this is to maintain a relative hyperglycaemia in order to supply the increased demand from the growing foetus (what actually result is hypoglycaemia as the foetus draws much of the body’s glucose, at least in the fasting state, across the placenta)
      • Glucose intolerance increases through to the end of pregnancy.  By the 3rd trimester, insulin levels are 50% higher than baseline to compensate.
    • After a meal, the excess glucose is normally controlled by a maternal insulin response.  However, decreased insulin sensitivity due to hormones means that a greater than average insulin response is required.  If the maternal response is inadequate, the foetus must then compensate.
      • Foetal hyperglycaemia/ hyperinsulinaemia causes
        • excess growth
        • conversion of glucose into fat
        • can cause hypoxia and a reactive polycythaemia

Pre-conception care

  • All patients with diabetes should be given advice about the avoidance of unplanned pregnancies.
  • Try and maintain an HbA1c of <6.1% if possible.  If not, try and reduce HbA1c as much as is safely possible.
    • Patients with an HbA1c of >10% should be advised against getting pregnant
    • As well as self-monitoring of BM, HbA1c should be measured monthly
      • NB Once pregnant HbA1c is not required in the 2nd and 3rd trimesters
  • Advice about weight loss should be given to diabetic women with a BMI >27kg/m²
  • A retinal and renal diabetic screen should also be carried out prior to conception

Drugs in pregnancy

  • Metformin can be continued but all other oral hyperglycaemic medication should be stopped
    • Insulin can be started if required
      • Aspart (novolog) or Lispro (humalog) are suitable short-acting insulins
      • Isophane insulin (Novolin/Humalin/Insulatard) is a suitable long-acting insulin
    • Stop ACE inhibitors/ARBs and statins during pregnancy

GDM Screening

  • Offer screening for GDM using the following risk factors:
    • BMI >30kg/m²
    • Previous macrosomic baby weighing >4.5kg
    • Previous GDM
    • First degree relative with diabetes
    • Family origin with a high prevalence of diabetes (south Asian, Black/caribbean and Middle Eastern)
  • Screening can be in the form of
    • early self-monitoring of glucose
    • 2 hour 75mg oral glucose tolerance test (OGTT) at 16-18 weeks (usually if the patient has had GDM in the past)
      • Test again at 28 weeks if this test is normal or if there are any other risk factors
      • NB Do NOT offer fasting plasma glucose, random blood glucose, glucose challenge or urinalysis for the diagnosis of GDM

Antenatal Care

  • Advise women to test fasting and 1-hour post prandial blood glucose levels after every meal.  They should also, ideally, test blood sugars before bed.
    • Advise to aim between 3.5-5.9mmol/l (fasting) and <7.8mmol/l (post-prandial)
    • Most women with newly diagnosed gestational diabetes will respond to diet/exercise
  • In women on insulin
    • advise about hypoglycaemia (particularly that it can be subtle/unknown)
    • offer glucagon for women with T1DM on insulin for hypoglycaemic attacks
      • also offer ketone strips to allow self-testing of ketoacidosis (if DKA does occur, patient should be admitted)
    • for those who are not managing self-injecting, consider the use of an insulin pump
  • Retinal assessment
    • at first opportunity (if no recent screening results)
      • if normal, screen again at 28 weeks
      • if abnormal, screen again at 16-20 weeks
  • Renal assessment
    • at first opportunity
      • refer to nephrology if serum creatinine is high (>120μmol/l) or total protein excretion >2g/day
      • thromboprophylaxis if proteinuria >5g/day
  • Scans
    • As well as routine aging scan (around 7-10 weeks) and anomaly scan (18-20 weeks)
      • USS monitoring of foetal growth should be measured every 4 weeks from 28-36 weeks (i.e. 28, 32 and 36 weeks)
    • NB At the anomaly scan, look particularly at the outflow tracts and a 4-chamber view of the foetal heart
  • Offer weekly tests of foetal well being from 38 weeks and consider induction of labour if there are any signs of distress
  • Management
    • Most mothers with newly diagnosed gestational diabetes will manage with diet/exercise alone.  HOWEVER, if there is any evidence of complications (including macrosomia) or if blood glucose is not adequately controlled by diet/exercise alone, insulin and/or oral hypoglycaemics should be used to manage the diabetes.

Intrapartum care

  • NB Vaginal birth should be advised against if there has been previous C-section or if the patient has bad retinopathy.  Macrosomia is also a relative indication for C-section.
  • During delivery, monitor blood glucose hourly, aiming between 4 and 7 mmol/l
    • Every 30 mins if GA is used
    • If not controlled, consider IV dextrose + insulin (also for women with T1DM)

Postpartum Care

  • If there are no problems the baby can stay with the mother.  The baby should be treated in a neonatal intensive care unit if they:
    • are hypoglycaemic with abnormal signs (all babies should have their blood glucose checked 2-4 hours after birth or if they have signs of hypo/hyperglycaemia)
    • show any signs of respiratory distress, jaundice requiring treatment, cardiac decompensation, encephalopathy or polycythaemia
    • need IV fluids
    • need tube feeding (particularly if blood glucose is low- <2mmol/l- on two consecutive readings despite adequate feeding)
      • NB advise mother to attempt to feed baby as soon as possible (ideally within 30 mins) to get glucose levels to normal
    • is preterm.
  • IV dextrose and insulin should be given if there are clinical signs of hypoglycaemia or if orogastric feeding doesn’t increase glucose levels adequately

Postnatal Care

  • For women with pre existing DM
    • Don’t restart oral hyperglycaemic medications that were stopped until breastfeeding has stopped
      • metformin and glibenclamide are safe
    • reduce insulin levels immediately following birth to adequately control glucose levels
    • advise about the risk of hypoglycaemia whilst breast feeding (make sure they eat beforehand etc)
    • can go back to routine diabetic care/treatment
  • For women with GDM,
    • all hyperglycaemic medications should be able to be stopped
    • offer a fasting plasma glucose level at 6-weeks post-natal appt, then annually
  • Generally
    • Advice about weight, lifestyle, exercise etc
    • Advice about risks in future pregnancies
    • Offer ophthalmology follow-up if retinopathy was diagnosed/worsened during pregnancy

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