The following is a research paper that I wrote for my doula training. I realize that the issue of Gestational Diabetes is not simple. I hope that this is helpful to bring greater clarity to the purposes of screenings & most importantly, what are the key issues for moms to improve their own health & the health of their babies.
A sweet syrupy beverage, an hour wait and a blood draw have become a rite of passage for pregnant women between week 24-28 of pregnancy. Although the Glucose Challenge Test and the follow-up Glucose Tolerance Test could be useful as indicators of risk for Gestational Diabetes Mellitus (GDM), the lack of a gold standard for diagnosis is problematic. In addition, questions remain in regards to whether or not identification and treatment of women with GDM will prevent some of the associated adverse perinatal outcomes, and if there is enough evidence to support wide screening for GDM in low risk, asymptomatic mothers.
Not until 1973 was an attempt made to link an abnormal glucose tolerance test with the absence of overt disease to perinatal outcomes. Though the correlation was tenuous, it gave rise to GDM as a disease entity to be searched for and treated
From the concept of prediabetes, GDM evolved as a pathology in blood glucose absorption and insulin resistance before an individual is truly insulin dependent. The Glucose Challenge Test purports to uncover a defect in the glucose balance which is then to be confirmed with a Glucose Tolerance Test to officially diagnose GDM.
Abnormally high levels of glucose in the blood are used to identify GDM. GDM is defined as an impaired glucose tolerance with the onset or first recognition during pregnancy. Therefore, a woman with no diabetes before pregnancy who presents with high blood glucose levels during pregnancy, following a Glucose Challenge Test and a follow-up Glucose Tolerance Test, is diagnosed as having GDM.
GDM affects how the cells in a woman’s body during pregnancy use glucose. Although the cause is not firmly agreed on, there are clues to why a woman’s body during pregnancy becomes unable to make and utilize all the insulin it needs.
Even with conservative estimates, GDM affects almost 1 in 20 pregnancies. Some cite impaired glucose tolerance in as many as one-third of women. Data, according to the Centers for Disease Control, suggest a prevalence of GDM in 2010 was between 4.6% to 9.2%, depending on the diagnostic criteria used, of all pregnancies.
Although the true prevalence of GDM is unknown, impaired glucose tolerance and insulin resistance can result in excessively high glucose levels for expectant mothers and their developing babies. The challenge in determining the prevalence of GDM is that the prevalence percentages are very sensitive to the diagnostic criteria used. The criteria has changed and continues to change mainly due to a lack of consensus resulting in the absence of a gold standard of blood glucose levels for the diagnosis of GDM.
During regular digestion in a non-diabetic individual, the breakdown of food leads to glucose entering the blood stream. The pancreas produces insulin to meet the load of glucose in the blood stream. The insulin serves as a key to the cells, moving glucose from the blood to the cells to be used as energy.
During pregnancy, however, there are normal changes in glucose metabolism that are necessary to promote the baby’s growth. Human Placental Lactogen and other placental hormones diminish the effect of insulin in the mother’s body with the key purpose of allowing more glucose to cross the placenta to nourish the baby. The placental hormones support the baby’s development, but also block the action of the mother’s insulin creating insulin resistance. The action of the placental hormones causes the mother’s body to increase insulin production in order to deliver blood glucose to her own cells to be used for energy. A modest elevation in blood glucose following meals is normal during pregnancy.
Although normal in a healthy pregnancy for maternal cells to be less responsive to insulin, if the pancreas cannot keep up with the load of blood glucose, blood sugar levels will rise too high. At that point, as the pancreas works overtime to produce insulin, the blood glucose levels continue to remain high. Without enough insulin, the key to opening the mother’s cells, the glucose cannot leave the blood and be changed into energy.
GDM generally affects mothers late in pregnancy after the baby’s body has been formed, but while the baby is still busy growing. As the baby grows, the placenta produces increasingly more insulin blocking hormones. Glucose builds up in the blood at high levels that can affect the growth and welfare of the baby.
Insulin from the mother does not cross the placenta; however, blood glucose does. The increased amount of blood glucose available to the baby as it crosses the placenta forces the baby’s pancreas to react by increasing insulin production. The high blood glucose delivers more energy than the baby needs often leading to excessive growth or a large size. Uncontrolled GDM has risks and concerns about the baby’s size, an increased risk of cesarean section, low blood glucose levels for the baby at birth and respiratory distress at birth. Also cited in literature are the possible long term adverse outcomes such as an increased risk of obesity and development of Type 2 Diabetes (Non-Insulin Dependent Diabetes Mellitus or NIDDM).
The current standard of care for expectant mothers includes a routine screening for GDM. The initial Glucose Challenge Test protocol requires the mother to drink a sugary solution. Blood is drawn at one hour. If the blood glucose is less than 130-140 mg/dL, it is considered normal. However, if the blood glucose is higher, it means that the mother is at a higher risk for GDM.
With a high blood glucose measure on the one hour Glucose Challenge Test, the mother is then referred for a follow-up Glucose Tolerance Test. The mother is expected to fast overnight. First, a fasting blood glucose blood draw is taken. Next the mother drinks another sugary solution, but this time with a higher concentration of glucose. Her blood glucose is then checked every hour for three hours. If at least two of her blood glucose results are higher than normal, she is formally diagnosed with GDM.
The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study was a response to the need for an internationally agreed upon diagnostic criteria for GDM based upon their value for predicting adverse outcomes in pregnancy. The primary criteria used in the United States are the National Diabetes Data Group (NDDG), The Carpenter and Coustan Criteria (CC) and the International Association of Diabetes and Pregnancy Study Groups (IADPSG). The NDDG and CC are recommended by the American Congress of Obstetricians and Gynecologists (ACOG) and when applied result in GDM diagnosis in about 5-6% of pregnancies. The American Diabetes Association (ADA) recommends IADPSG resulting in a prevalence of 18-20% of pregnancies. Medical experts do not agree on a single set of screening guidelines for GDM.
There is, however, agreement that mothers are at a high risk for GDM if their Body Mass Index (BMI) is greater than 30, if they previously had GDM, and if there is a strong family history of diabetes. In addition, advanced maternal age, higher parity, nonwhite race and overweight correlate with an increased risk of GDM. The increase in perinatal mortality associated with an abnormal Glucose Tolerance Test can already be predicted as much by the indications for testing such as obesity, large fetus or a previous stillbirth.
The adverse outcomes most commonly associated with GDM are fetal macrosomia (birth weight greater than 90th percentile for gestational age), increased rates of cesarean delivery, shoulder dystocia and birth trauma. A baby may be too large to enter the birth canal or the head may enter, but the shoulders may become stuck. Evidence does support a positive association between an abnormal Glucose Tolerance Test, increasing blood glucose levels and macrosomia; although, the majority of macrosomic infants are born to moms who have normal Glucose Tolerance Tests.
Severe GDM can result in stillbirth. There is also an increased risk of preeclampsia and hypertensive disorders. Indeed, there are direct risks to the baby, as he may experience newborn hypoglycemia, jaundice, lung immaturity and breathing difficulties.
For the mother with GDM, even if blood glucose levels return to normal following pregnancy, she has an increased risk of developing NIDDM or Type 2 diabetes later in life. In addition, she risks GDM during subsequent pregnancies. There are also potential long term consequences of GDM for the baby as he grows up such as glucose intolerance and obesity.
GDM has a small, but important risk of adverse perinatal outcomes and also long term risks for mother and for child. Even with these positive associations, however, no clear threshold of blood glucose levels for increased risk has been found. Uncertainty remains as to the level of glucose impairment associated with adverse perinatal outcomes.
The cornerstone of treatment for mothers diagnosed with GDM is dietary and nutritional management. Blood glucose monitoring, exercise, medications and close monitoring of the baby to include fetal measurements also figure into most treatment plans. Through intervention and treatment, the risk of neonatal complications such fetal macrosomia, shoulder dystocia, cesarean section rate and hypertensive disorders may be decreased.
Different reviews of literature point to varying evidence of improved outcomes with treatment. The majority of studies appear to support the concept that treatment involving diet and blood glucose monitoring is not harmful to mother and baby and will more likely result in a baby that weighs less than 8 pounds 13 ounces.
Health outcomes of those with GDM as identified by screenings are still not solidly verified with or without treatment. The Glucose Tolerance Test results are not reproducible. A positive test may unduly label a pregnancy as “high risk” leading to extensive, expensive programs of tests and interventions with unproven benefit. Negative test results may be falsely reassuring that the risk has been removed. These issues certainly call into question the broad application of these screenings to all women, symptomatic or asymptomatic, at 24-28 weeks gestation.
Clinical judgment based on the assessment of pre-pregnancy weight, pregnancy weight gain and a pregnancy past 42 weeks gestation is more predictive of fetal macrosomia than the Glucose Tolerance Test. BMI, previous pregnancies with GDM and a family history of diabetes may be more predictive of impaired glucose tolerance and insulin resistance. If the wide application of the Glucose Challenge Test and the Glucose Tolerance Test have limited value, perhaps interventions to mitigate obesity and modify lifestyle would be a more effective treatment.
Preconception and early intervention in pregnancy in regards to body weight and lifestyle such as diet, activity and exercise, may result in improved glucose tolerance before the pancreas is overtaxed resulting in excessively high blood glucose that leads to adverse neonatal outcomes.
Researchers reported that women with a history of GDM who reach an ideal body weight after delivery decrease their risk of developing NIDDM or Type 2 diabetes. Those mothers with GDM who breastfed increased their postpartum weight loss which was also associated with a decreased risk of developing NIDDM.
With more than one-half of pregnant women considered overweight or obese according to ACOG, obesity associated GDM could potentially be prevented by targeting the risks and lifestyles of the women in that category with BMI 25-29.9 (overweight) and 30-34.9 (obese). Preventing obesity using healthy eating and regular exercise is the key component to women’s health care before and after conception. Eating healthy foods, keeping active and losing excess pounds, before pregnancy if possible, may be the best preventative care and treatment plan.
GDM, even with its lack of a gold standard of diagnostic blood glucose levels, is undeniably a risk for both mother and baby in the short term, pregnancy, and as well as long term, into the foreseeable future. Risk factors for GDM such as a high BMI, especially greater than 30, should be addressed early in pregnancy. If overt symptomatic diabetes is suspected, blood glucose testing should be done. However, the evidence does not support the broad net approach of screening utilizing the Glucose Challenge Test between 24-28 weeks gestation.
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