Gestational diabetes is a metabolic condition occurring during pregnancy whereby blood sugar levels are not properly regulated. Type II diabetes, also known as diabetes mellitus, is often associated with blood sugar regulation/dysfunction post-delivery.
Babies born to people who already have type II diabetes have double the risk of serious injury at birth, are three times as likely to be delivered by caesarean, and four times the incidence of requiring newborn intensive care unit (NICU) admission.
Gestational diabetes is the most prevalent sort of diabetes occurring during pregnancy (90 per cent), with pre-existing type II diabetes accounting for another eight per cent. There are screening programs in place globally to check for gestational diabetes.
Who gets gestational diabetes?
Abnormal glucose regulation is found in 3-10 per cent of pregnancies. Ethnic background plays a large part in who does and doesn’t develop gestational diabetes, with people of colour being diagnosed more frequently.
Recurrence risk with future pregnancies is high, and the risk of developing type II diabetes within five years after the first delivery is about one in three.
High risk populations have a 50 per cent higher chance. Anyone can develop gestational diabetes, but some groups have higher risks than others.
Why does gestational diabetes occur?
It is understood that the absorption of glucose in the digestive tract is markedly lowered, meaning the absorption rate of glucose is not the cause of hyperglycaemia (low blood sugar levels).
It is normal to have a rise in blood glucose during pregnancy, with subsequent secretion of insulin from the pancreas. This allows sufficient glucose to be made available to support the person and the foetus.
Read more about insulin resistance
During pregnancy, low blood sugar occurs between meals and during sleep, as the foetus draws glucose across the placenta from the blood regardless of the time of day. Glucose demand of the foetus increases as the pregnancy goes on.
The levels of certain hormones and steroids increases during pregnancy, causing increasing insulin resistance. This means more insulin is required, increasing over the pregnancy.
In the third trimester, insulin levels are twice as high as when not pregnant. If the insulin response from the adult pancreas is not sufficient, hypoglycaemia results for both the person and the foetus. This can result in recurrent hyperglycaemia after eating, being the major cause of accelerated growth by the foetus.
When insulin surges, the foetus has episodes of hyperinsulinaemia (too much insulin). This state causes excess nutrient storage, resulting in a large foetus.
This conversion of excess glucose into fat in the foetus also causes lowered oxygen levels in the foetus. Lowered oxygen levels (foetal hypoxia) causes a surge in adrenal hormones, which then subsequently cause a range of secondary problems in the foetus ranging from high blood pressure (hypertension), an increase in red blood cells, poor circulation, and heart problems.
Birth defects (anatomical abnormalities) often occur in the first trimester, so diabetes screening is important very early or prior to conception.
Gestational diabetes screening and diagnosis
Screening typically consists of a one-hour glucose challenge test (GCT) and a three-hour oral glucose tolerance test (OGTT) if a person has an abnormal GCT result.
High-risk people or in those where insulin resistance prevalence is five per cent or higher (such as in the southern United States), the three-hour test may be the first port of call.
Gestational diabetes screening is typically checked after 24 weeks of pregnancy in those with no previous diagnosis of diabetes type I or II.
Type I diabetes diagnosis in pregnancy – rare
Type I diabetes is usually diagnosed in childhood or adolescence, and rarely diagnosed during pregnancy.
Those diagnosed during pregnancy may present to an emergency ward in an unexpected coma due to early pregnancy possibly provoking diet and blood sugar (glycaemic) control instability.
Type II diabetes diagnosis in pregnancy – more common
Diagnosis of type II diabetes during pregnancy is tested for in the following ways:
- A blood test for haemoglobin A1C (HbA1C) of 6.5 per cent
- Fasting plasma (blood) glucose over 126 mg/dL (7.0 mmol/L)
- A two-hour plasma glucose level of 200 mg/dL (11.1 mmol/L) during a 75-g OGTT
- A random plasma glucose level of 200 mg/dL (11.1 mmol/L) in a person who has symptoms of hyperglycaemia or hyperglycaemic crisis
- A repeat test will be done to confirm findings if necessary
Risk of those with prediabetes
Anyone identified before pregnancy with prediabetes is considered at a very high risk for developing gestational diabetes during pregnancy. Early screening in the first trimester is recommended.
After diagnosis of gestational diabetes in pregnancy
Continued testing will be required during pregnancy, with first, second and third trimesters with different screening methods. All testing is centred around blood tests and ultrasound, with some patients requiring electrocardiography (heart monitoring).
Managing gestational diabetes
The most important factor in managing diabetes is diet, with the recommendation being to eat smaller meals more often to keep blood sugar stable.
Diabetes diets include foods that reduce glycaemic load after eating, meaning food choices should include foods that take longer to be digested.
These foods then release their sugars slower into the blood, thus avoiding blood sugar instabilities. Insulin therapy may be recommended to get the body’s levels of insulin more like those of a nondiabetic pregnant person.
Early intervention with insulin is often used when diet isn’t producing the best results. Glyburide and metformin Insulin has offered a safe route for those with gestational diabetes during pregnancy, however oral doses of glyburide and metformin are also considered safe options at this stage.
Longer-term studies of adverse outcomes of these drugs on a foetus are thin on the ground, making this a concern to be addressed with your doctor.
About glyburide during pregnancy
Glyburide, also known as glibenclamide, is a medication prescribed for type II diabetes that is used with diet and exercise, and possibly other antidiabetic medication. This drug may be prescribed during pregnancy, and can be used during breastfeeding as it is not transferred to milk.
Glyburide increases the release of insulin from the pancreas. This drug is minimally transported across the placenta Glyburide is considered by many to be as safe and effective than metformin or insulin in gestational diabetes.
Factors that contribute to the failure of glyburide for managing blood sugar levels include increasing age, earlier gestational age at diagnosis, multiple pregnancies, and higher mean fasting glucose levels.
Glyburide should not be used in the first trimester because effects on the embryo are not known. Side-effects can include nausea and heartburn, and hypoglycaemia, among other issues. Speak to your doctor for more information.
About metformin during pregnancy
Metformin is used to treat type II diabetes, particularly in those who are overweight. Metformin is also used to treat polycystic ovarian syndrome (PCOS), which has links with insulin resistance.
Metformin works by decreasing glucose production by the liver and increasing insulin sensitivity of tissues. Metformin has not shown any clear harm to the foetus during pregnancy, but insulin may be the preferred treatment over either metformin or glyburide to be on the safe side.
Short-term safety of metformin during pregnancy is noted in scientific research, but long-term safety has not been established. Metformin crosses the placenta and umbilical cord levels have been shown to be high. When compared with insulin use in pregnant women, metformin is associated with less weight gain and less risk of developing pre-eclampsia.
Babies born to those treated with metformin have less visceral fat, which may have an impact on insulin resistance developing later in life. Side-effects can include diarrhoea, nausea and abdominal pain, with a low risk of hypoglycaemia.
Those with liver or kidney problems should avoid metformin. Babies born to those with gestational diabetes Babies will need to be monitored and treated if necessary.
Early oral feeding, preferably breastfeeding, and frequent blood glucose checks are recommended. Risks of serious injury at birth, caesareans, and NICU admission are much higher in babies born to people with gestational diabetes, and this is proportionally related to the degree of hyperglycaemia experienced during pregnancy.
Risks of gestational diabetes to the foetus
- Miscarriage risk increased, sometimes up to 44 per cent
- Major birth defects risk increases 4- to 8-fold (compared to 1-2 per cent of the general population)
- Birth defects often involve the cardiovascular and central nervous system, but include neural tube defects, genitourinary, gastrointestinal and skeletal abnormalities
- The diabetic status of the person whose sperm is used does not appear to increase the risk of birth defects
- Development of gestational diabetes after the first trimester is also not associated with an increase in birth defects, suggesting that the pre-conception and early conception periods are the main determinant of birth defects
- Well-controlled diabetes during pregnancy comes with the same or slightly elevated risk of birth defects as the general population
- Growth restriction in a foetus may occur in those with pre-existing type I diabetes
- Foetal growth restriction is connected to underlying vascular disease (high blood pressure or other diabetes-related vascular issues) in the person carrying the foetus
- Large baby, with abdominal circumference increasing beyond normal ranges past 24 weeks of pregnancy, more likely with pre-existing type II diabetes
- Increased incidence of caesarean section deliveries
- Children often have excessive body fat stores throughout life
- Excessive weight gain during pregnancy increases the risk of preterm delivery, having a large baby, and caesarean delivery
- Weight gain below regular standards increases the chances of having a baby born that is small for gestational age
- Macrosomia – large baby (birth weight above the 90th percentile for gestational age or greater than 4kg) occurs in up to 45 per cent of babies born to diabetics
- Anyone who is obese has double the risk of having a large baby, independent of diabetic status
- Large babies have more health problems than normal-size babies
- Babies born to diabetics have a larger shoulder and extremity circumference, decreased head-to-shoulder ratio, significantly higher body fat, and thicker arm skin folds, but head size is not affected
- Large babies are more at risk of birth injuries due to their size during labour, which means caesarean may be the safest route of delivery
- Impaired glucose tolerance and higher insulin levels (resulting in high blood pressure, obesity, other metabolic issues) are more common in children born to diabetics
- One study found that low socioeconomic status and gestational diabetes are associated with an increased risk of attention-deficit/hyperactivity disorder (ADHD) and compromised neurobehavioural functioning at age 6
- The risk of foetal death during birth is twice that of nondiabetic populations
- Hypoglycaemia at birth – can result in seizures, coma and brain damage
- Low serum calcium
- Hyperbilirubinaemia – jaundice
- Respiratory issues – risk of respiratory distress may increase until 38.5 weeks due to lung maturity occuring later
Managing diet for pregnant diabetics
- Avoid large meals – instead eat six smaller meals, with three main meals plus three snacks
- Avoid too many carbohydrates – no more than 50 per cent of the diet (ideally 35-40 per cent), with proteins and fats making up the rest
- Have a trained professional guiding diet, particularly in those who are obese
- Calcium and vitamin D supplements at 24-28 weeks gestation may help metabolic profile
- Pre-existing diabetes requires modification of insulin regime, plus diet management
References
- Wilmot EG, Mansell P. Diabetes and pregnancy. Clin Med (Lond). 2014 Dec. 14 (6):677-80.
- American Diabetes Association. Standards of medical care in diabetes–2010. Diabetes Care. 2010 Jan. 33 Suppl 1:S11-61.
- Moore LE, Clokey D, Rappaport VJ, et al. Metformin compared with glyburide in gestational diabetes: a randomized controlled trial. Obstet Gynecol. 2010 Jan. 115(1):55-9.
- Baptiste-Roberts K, Barone BB, Gary TL, et al. Risk factors for type 2 diabetes among women with gestational diabetes: a systematic review. Am J Med. 2009 Mar. 122(3):207-214.e4.
- Boinpally T, Jovanovic L. Management of type 2 diabetes and gestational diabetes in pregnancy. Mt Sinai J Med. 2009 Jun. 76(3):269-80.
- Ehrenberg HM, Mercer BM, Catalano PM. The influence of obesity and diabetes on the prevalence of macrosomia. Am J Obstet Gynecol. 2004 Sep. 191(3):964-8.
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