Gestational diabetes is a condition in which a woman without diabetes develops high blood sugar levels during pregnancy. Gestational diabetes generally results in few symptoms; however, it does increase the risk of pre-eclampsia, depression, and requiring a Caesarean section. Babies born to mothers with poorly treated gestational diabetes are at increased risk of being too large, having low blood sugar after birth, and jaundice. If untreated, it can also result in a stillbirth. Long term, children are at higher risk of being overweight and developing type 2 diabetes.
Gestational diabetes is caused by not enough insulin in the setting of insulin resistance. Risk factors include being overweight, previously having gestational diabetes, a family history of type 2 diabetes, and having polycystic ovarian syndrome. Diagnosis is by blood tests. For those at normal risk screening is recommended between 24 and 28 weeks’ gestation. For those at high risk testing may occur at the first prenatal visit.
Prevention is by maintaining a healthy weight and exercising before pregnancy. Gestational diabetes is treated with a diabetic diet, exercise, and possibly insulin injections. Most women are able to manage their blood sugar with a diet and exercise. Blood sugar testing among those who are affected is often recommended four times a day. Breastfeeding is recommended as soon as possible after birth.
Gestational diabetes affects 3–9% of pregnancies, depending on the population studied. It is especially common during the last three months of pregnancy. It affects 1% of those under the age of 20 and 13% of those over the age of 44. A number of ethnic groups including Asians, American Indians, Indigenous Australians, and Pacific Islanders are at higher risk. In 90% of people gestational diabetes will resolve after the baby is born. Women, however, are at an increased risk of developing type 2 diabetes.
Classical risk factors for developing gestational diabetes are:
Polycystic Ovary Syndrome
A previous diagnosis of gestational diabetes or prediabetes, impaired glucose tolerance, or impaired fasting glycaemia
A family history revealing a first-degree relative with type 2 diabetes
Maternal age – a woman’s risk factor increases as she gets older (especially for women over 35 years of age).
Ethnicity (those with higher risk factors include African-Americans, Afro-Caribbeans, Native Americans, Hispanics, Pacific Islanders, and people originating from South Asia)
Being overweight, obese or severely obese increases the risk by a factor 2.1, 3.6 and 8.6, respectively.
A previous pregnancy which resulted in a child with a macrosomia (high birth weight: >90th centile or >4000 g (8 lbs 12.8 oz))
Previous poor obstetric history
Other genetic risk factors: There are at least 10 genes where certain polymorphism are associated with an increased risk of gestational diabetes, most notably TCF7L2.
In addition to this, statistics show a double risk of GDM in smokers. Polycystic ovarian syndrome is also a risk factor, although relevant evidence remains controversial. Some studies have looked at more controversial potential risk factors, such as short stature.
About 40–60% of women with GDM have no demonstrable risk factor; for this reason many advocate to screen all women. Typically, women with GDM exhibit no symptoms (another reason for universal screening), but some women may demonstrate increased thirst, increased urination, fatigue, nausea and vomiting, bladder infection, yeast infections and blurred vision.
A 2015 review found that when done during pregnancy moderate physical exercise is effective for the prevention of gestational diabetes. A 2014 review however did not find a significant effect.
Diet and physical activity interventions designed to prevent excessive gestational weight gain reduce the rates of gestational diabetes. However, the impact of these interventions varies with the body-mass index of the person as well as with the region in which the studies were performed.
It has been suggested that for women who have had gestational diabetes, support between pregnancies may lower their chances of having gestational diabetes again in future pregnancies. This support might include diet and exercise, education, and lifestyle advice. However, there is no research to show whether interventions between pregnancies lower the number of women who develop gestational diabetes again.
Theoretically, smoking cessation may decrease the risk of gestational diabetes among smokers.
Gestational diabetes generally resolves once the baby is born. Based on different studies, the chances of developing GDM in a second pregnancy, if a woman had GDM in her first pregnancy, are between 30 and 84%, depending on ethnic background. A second pregnancy within 1 year of the previous pregnancy has a large likelihood of GDM recurrence.
Women diagnosed with gestational diabetes have an increased risk of developing diabetes mellitus in the future. The risk is highest in women who needed insulin treatment, had antibodies associated with diabetes (such as antibodies against glutamate decarboxylase, islet cell antibodies and/or insulinoma antigen-2), women with more than two previous pregnancies, and women who were obese (in order of importance). Women requiring insulin to manage gestational diabetes have a 50% risk of developing diabetes within the next five years. Depending on the population studied, the diagnostic criteria and the length of follow-up, the risk can vary enormously. The risk appears to be highest in the first 5 years, reaching a plateau thereafter. One of the longest studies followed a group of women from Boston, Massachusetts; half of them developed diabetes after 6 years, and more than 70% had diabetes after 28 years. In a retrospective study in Navajo women, the risk of diabetes after GDM was estimated to be 50 to 70% after 11 years. Another study found a risk of diabetes after GDM of more than 25% after 15 years. In populations with a low risk for type 2 diabetes, in lean subjects and in women with auto-antibodies, there is a higher rate of women developing type 1 diabetes (LADA).
Children of women with GDM have an increased risk for childhood and adult obesity and an increased risk of glucose intolerance and type 2 diabetes later in life. This risk relates to increased maternal glucose values. It is currently unclear how much genetic susceptibility and environmental factors contribute to this risk, and whether treatment of GDM can influence this outcome.
Relative benefits and harms of different oral anti-diabetic medications are not yet well understood as of 2017.
There are scarce statistical data on the risk of other conditions in women with GDM; in the Jerusalem Perinatal study, 410 out of 37962 women were reported to have GDM, and there was a tendency towards more breast and pancreatic cancer, but more research is needed to confirm this finding.
GDM poses a risk to mother and child. This risk is largely related to uncontrolled blood glucose levels and its consequences. The risk increases with higher blood glucose levels. Treatment resulting in better control of these levels can reduce some of the risks of GDM considerably.
The two main risks GDM imposes on the baby are growth abnormalities and chemical imbalances after birth, which may require admission to a neonatal intensive care unit. Infants born to mothers with GDM are at risk of being both large for gestational age (macrosomic) in unmanaged GDM, and small for gestational age and Intrauterine growth retardation in managed GDM. Macrosomia in turn increases the risk of instrumental deliveries (e.g. forceps, ventouse and caesarean section) or problems during vaginal delivery (such as shoulder dystocia). Macrosomia may affect 12% of normal women compared to 20% of women with GDM. However, the evidence for each of these complications is not equally strong; in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study for example, there was an increased risk for babies to be large but not small for gestational age in women with uncontrolled GDM. Research into complications for GDM is difficult because of the many confounding factors (such as obesity). Labelling a woman as having GDM may in itself increase the risk of having an unnecessary caesarean section.
Neonates born from women with consistently high blood sugar levels are also at an increased risk of low blood glucose (hypoglycemia), jaundice, high red blood cell mass (polycythemia) and low blood calcium (hypocalcemia) and magnesium (hypomagnesemia). Untreated GDM also interferes with maturation, causing dysmature babies prone to respiratory distress syndrome due to incomplete lung maturation and impaired surfactant synthesis.
Unlike pre-gestational diabetes, gestational diabetes has not been clearly shown to be an independent risk factor for birth defects. Birth defects usually originate sometime during the first trimester (before the 13th week) of pregnancy, whereas GDM gradually develops and is least pronounced during the first and early second trimester. Studies have shown that the offspring of women with GDM are at a higher risk for congenital malformations. A large case-control study found that gestational diabetes was linked with a limited group of birth defects, and that this association was generally limited to women with a higher body mass index (≥ 25 kg/m²). It is difficult to make sure that this is not partially due to the inclusion of women with pre-existent type 2 diabetes who were not diagnosed before pregnancy.
Because of conflicting studies, it is unclear at the moment whether women with GDM have a higher risk of preeclampsia. In the HAPO study, the risk of preeclampsia was between 13% and 37% higher, although not all possible confounding factors were corrected.
Gestational diabetes affects 3–10% of pregnancies, depending on the population studied.