Cochrane: Evidence is insufficient to permit judgement of which is the best way to identify women who have gestational diabetes. Insulin is a hormone
produced in the pancreas that enables cells to absorb glucose to turn
it into energy. During pregnancy, maternal resistance to insulin
develops so that glucose can more easily cross the placenta to the growing foetus. Resistance to insulin becomes apparent in the second trimester and declines progressively to term.
Insulin
resistance returns to normal after pregnancy, usually within six weeks
of birth. For about seven in every 100 pregnant women, resistance to
insulin is excessive, and the woman’s blood sugar becomes too high. This
is known as gestational diabetes.
If gestational diabetes develops and resistance to maternal insulin
becomes too great, high fetal blood insulin can develop and may cause
increased growth and fat deposits, increased birthweight and perinatal
complications. The woman and her baby can be harmed by high blood sugar
levels if untreated, and harmful effects may remain after pregnancy.
Growing knowledge shows that infants of women who have had gestational
diabetes are at increased risk of obesity and high blood pressure later in life.
Lowering blood sugar levels can reduce the harmful effects, but women
can receive treatment only if they are clearly identified. Several
tests are used to find out whether a woman has gestational diabetes.
Most involve giving a sugary drink and taking a series of blood tests
over one to three hours; this is known as the oral
glucose tolerance test (OGTT). Limitations of the OGTT are that it
requires women to fast from the night before, to drink a glucose
solution and to wait for two or three hours before having the final
blood test. Other tests have been proposed that do not require this
level of involvement by the pregnant woman or by healthcare staff. Using
different tests and different criteria (glucose thresholds that define
gestational diabetes) will influence identification of women diagnosed.
This review
aimed to determine the best way of identifying women with gestational
diabetes. We identified six small randomised trials (involving 694
women) of unclear quality, which compared different ways of giving a
glucose load. None evaluated the important question of what time during
pregnancy is best to test women for gestational diabetes, and no studies
compared the 75-gram or 100-gram OGTT with other strategies. Large
well-designed trials are needed to provide information about the best
way to identify women with gestational diabetes.