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Short- and long-term effects of gestational diabetes and foetal outcomes


  • Gestational diabetes (GDM) affects around 3.5% of pregnancies in the United Kingdom and has a higher prevalence in obese pregnant women.

  • Maternal hyperglycaemia increases risk of adverse pregnancy outcomes and GDM is associated with adverse outcomes for women and their offspring both in the short and long term.

36.1

Maternal diabetes and insulin resistance

  • Pregnancy is a state of increasing insulin resistance (up to 40%–50%), with most of this increase occurring in the third trimester.

  • In obese pregnant women, the prepregnancy insulin resistance associated with obesity is exacerbated such that obese pregnant women tend to have reduced peripheral insulin sensitivity even in early pregnancy.

  • Increased adipose tissue in obese women also leads to a greater release of inflammatory markers and free fatty acids, which further contribute to insulin resistance, and inhibits the action of insulin on suppressing lipolysis.

  • In the 1950s Pederson first postulated that in utero exposure to hyperglycaemia due to maternal diabetes may cause long-term changes to the foetus including congenital malformations, increased birthweight, and increased risk of diabetes and obesity later in life.

  • An increasing body of evidence has characterised associations of maternal hyperglycaemia with offspring size and cardiovascular health.

  • There are longer term risk of maternal cardiovascular disease, chronic kidney disease, and cancer risk.

36.2

Short-term risks

36.2.1

Foetal risks

36.2.1.1

Increased foetal growth

  • Insulin resistance in later gestations helps facilitate nutrient transfer to the foetus and in turn promotes foetal growth.

  • In states of maternal overnutrition, such as maternal obesity and diabetes, further increased insulin resistance may lead to a greater supply of nutrients to the foetus and result in increased foetal growth, particularly of adipose tissue.

  • Studies of placentas from women with diabetes have identified increased expression of placental glucose transporters even with near-normal glycaemia at term.

  • This may have a significant impact on nutrient transfer to the foetuses of women with diabetes, even in the presence of good glycaemic control.

  • It has also been suggested that the resultant foetal hyperinsulinaemia may exacerbate the glucose concentration gradient across the placenta, further increasing glucose transfer to the foetus.

  • It is well established that there is a linear relationship between the level of maternal glycaemia during pregnancy with indices of growth such as offspring birthweight, adiposity, and BMI.

  • The Hyperglycaemia and Adverse Pregnancy Outcome study demonstrated raised maternal blood glucose at fasting, 1 and 2 hours after oral glucose tolerance test (OGTT) at 24–32 weeks’ gestation was associated with approximately 1–1.5-fold increased risk for neonatal macrosomia (birthweight >90th centile) and neonatal hyperinsulinaemia (via cord blood C-peptide).

36.3

Short-term clinical consequences of increased foetal size include

  • Polyhydramnios leading to increased risk of preterm labour, malpresentation, unstable lie, and cord prolapse.

  • Obstructed labour and increased likelihood of caesarean section delivery.

  • Foetal injury (including shoulder dystocia) or damage to the birth canal (including perineal or obstetric anal sphincter injury).

36.3.1

Congenital anomalies

Maternal hyperglycaemia can cause defects in the developing organs leading to congenital anomalies. Cardiac and neural tube defects are the most common.

36.3.2

Preterm birth

  • Women with GDM are more likely to deliver at preterm gestations. This is in part due to earlier induction of labour for iatrogenic reasons and premature rupture of membranes due to polyhydramnios.

  • Preterm neonates are at an increased risk of complications including difficulties with feeding and respiration, jaundice, infection, neonatal unit admission, and perinatal death.

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