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Chapter: Medicine Study Notes : Reproductive and Obstetrics

Gestational Diabetes Mellitus (GDM)

Any degree of glucose intolerance with onset or first recognition during pregnancy

Gestational Diabetes Mellitus (GDM)


·        = Any degree of glucose intolerance with onset or first recognition during pregnancy

·        For most it consists of mild glucose intolerance manifest during the 2nd or 3rd trimester and normalising following delivery


·        Affects 4 – 8 % of all pregnancies (Indian women >> than European).  Risk factors:

o  Maternal age > 35 years

o  Family history of diabetes

o  Previous macrosomia, unexplained still birth

o  Obesity 

o  Glycosuria on two or more separate occasions. 20% of women have glucose in their urine Þ not a reliable indicator


·        Associated with:

o  ­ Morbidity for mother – 1.5 times risk of caesarean delivery


o  Increased risk of type 2 diabetes in the mother (up to 50% over next 10 years). ?Would have got it anyway. Also hypertension, hyperlipidaemia, etc.


o  ­ 2.5 times morbidity for baby, including:


§  Large for gestational age, macrosomia (birth weight > 4000 gm – but most macrosomic babies‟ mothers have normal glucose tolerance)


§  ­Risk of inter-uterine fetal death (IUFD)


§  Possibly ­neonatal jaundice, polycythaemia, post-natal hypoglycaemia, prematurity – but not congenital malformations (unless IDDM mother)


o  But in general risks are low

·        Is usually asymptomatic (ie no polyuria and thirst). Risk factors have low predictive power Þ universal screening usual


·        NZ guidelines: 

o   All women should be tested for glucose intolerance following a 50g glucose load between 24 and 28 weeks, blood sample 1 hour later. Normal < 7.8. If very high risks (eg previous GDM) screen at 18 weeks as well 

o   If failed screening test then formal test is 75g fasting load with samples at 0,1 and 2 hours. Normal is <5.5, < 11 and < 8.5 at 0,1 and 2 hours. If any one is abnormal then GDM.


·        Exam: includes checks of eyes (retinopathy) and hands and legs (neuropathy), urine for protein


·        Aetiology: ­human placental lactogen (HPL, increases through pregnancy) ® ­insulin resistance ® ­insulin production. May unmask sub-clinical NIDDM.


·        Management:

o   Diet and exercise (but don‟t calorie restrict them – ketosis is bad for babies) 

o   Regular monitoring – home glucose monitoring and Hb A1C – normal is less than 6.5, under 8 acceptable. Aiming for pretty tight control 

o   Insulin used if unable to control levels, or evidence of macrosomia. Stop once labour starts – requirements fall dramatically after delivery

o   Sulphonylureas and metformin not approved in pregnancy 

o   ® ¯Frequency of macrosomia but less clear effect on perinatal mortality and rate of caesarean section 

o   Do GTT 6 weeks after delivery to check for type 1 or 2 diabetes

·        IDDM: 

o   Need to conceive when Hb A1C < 8. Even if tightly controlled, 4 – 5% risk of congenital abnormalities (2* general population). Most common are neural tube and heart defects

o   Check for retinopathy at least twice during pregnancy

o   Get baseline renal function and ECG/Echo if cardiac problems 

o   Usual insulin injections have shorter action Þ control harder. In early pregnancy, insulin requirements may reduce. Later they usually increase. 

o   Usually induced before term


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