Gestational diabetes

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Description

Gestational Diabetes Mellitus (GDM) is characterised by hyperglycaemia first recognised in pregnancy. Its prevalence varies widely in the literature, but is thought to effect 4-7.5% of all pregnancies  and is increasing  more common among older women, obese women and certain ethnic groups. It usually presents after the beginning of the second trimester.

Pathological Process

In pregnancy, women develop insulin resistance, which stems from increased maternal adiposity and several hormones produced during pregnancy block the action of insulin at a cellular level, i.e. Tumor Necrosis Factor Alpha, human placental lactogen and placental growth hormone. As a result, blood glucose levels rise and more insulin is produced in response. As the pregnancy develops, the insulin demands increase further, and insulin resistance also increases due to rising levels of pregnancy hormones. However, this is a normal physiological change in pregnancy. Beta cells in the pancreas increase insulin production to compensate for this, and so in normal pregnancy blood glucose level changes are small compared to the large changes in insulin resistance. In GDM, women have been shown to have less of a degree of compensation at the Beta cell than non-GDM women . <10% of GDM women have been shown to have antibodies to pancreatic islets of Beta cells in their circulation. It has been postulated thaqt their GDM may stem from autoimmune damage to Beta cells . Some GDM cases have been shown to be due to genetic defects in Beta cells . Others may be chronic hyperglycaemia first detected at pregnancy, which may explain why most GDM women go on to develop Diabetes Mellitus (DM). The exact mechanism for increased insulin resistance is still largely unclear. Maternal obesity may contribute as upregulation of cytokines and adipokines impacts insulin pathways and skeletal muscle insulin sigalling is impaired .

Consequences of Gestational Diabetes Mellitus

For Mother

GDM is related to higher rates of:

<span style="line-height: 1.5em;" />Pre-eclampsia

Caesarean section

GDM in subsequent pregnancies

GDM typically resolves after birth. However, there have been many studies detailing the significantly increased risk of developing DM Type II after having GDM, particularly in the first 5 years postpartum .

For Baby

• Macrosomnia: leading to higher rates of injury to mother and baby , and higher rates of childhood overweight and obesity 
• Fetal hyperglycaemia and hyperinsulinimia
• Preterm delivery
• Intensive neonatal care
• High neonatal body fat percentage
• Clinical neonatal hypoglycaemia 

Diagnositc Procedures

Risk Factors

Several factors have been identified which increase the risk of women developing GDM. These include:

Older age

Ethnicity, namely black, Native American, Pacific Islander, Hispanic, South or East Asian and Indigenous Australian

High pre-pregnancy BMI

Family history of diabetes

Previous GDM

Multigravid women

Excessive weight gain during pregnancy

Short stature

Smoking

Local regimens use various screening tools in conjunction with these risk factors to identify women in need of further testing.

Screening for Gestational Diabetes Mellitus

GDM can only be confirmed by an abnormal glucose tolerance test. The World Health Organisation classify GDM as:

• A fasting blood glucose level of >7mmol/l
• A blood glucose level of >7.8mmol/l 2 hours after a 75g glucose drink

Medical Management / Interventions

Diet

Dietary interventions have long been a cornerstone of treatement for GDM. Women diagnosed with GDM are routinely referred to a dietician. The challenge of GDM management for dieticians is striking the delicate balance between keeping maternal insulin low without restricting fetal growth. A Cochrane review in 2008 examined 3 trials investigating the effects of diet on preventing GDM, found inconclusive results .

Medication

When dietary management fails, insulin is considered the safest treatment, as free insulin cannot cross the placenta. Alpha-glucosidase inhibitors (acarbose) and biguanides (metformin) cross placenta but are still used increasingly. However, there are insufficient data to determine the long term effects of these on mother and baby .

Resources

Kim and Ferrera (2010) Gestational Diabetes During and After Pregnancy

References

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