Gestational Diabetes
Definition
Gestational diabetes (GDM) is defined as glucose
intolerance of variable degree with onset or first recognition during the
present pregnancy.
It can be screened by
drawing a 1-hour glucose level following a 50-g glucose load, but is
definitively diagnosed only by an abnormal 3-hour OGTT following a 100-g
glucose load.
Importance
The growth and maturation
of the fetus are closely associated with the delivery of maternal nutrients,
particularly glucose.
This is most crucial in the
third trimester and is directly related to the duration and degree of maternal
glucose elevation.
Thus, the negative impact
is as highly diverse as the variety of carbohydrate intolerance that
women bring to pregnancy.
For the mother with GDM
there is a higher risk of
·1
hypertension,
·2
preeclampsia,
·3
urinary tract
·4
infections,
·5
cesarean section, and
·6
future diabetes.
Many of the problems
associated with overt diabetic pregnancies can be seen in infants of gestational
diabetic pregnancies, such as
·7
macrosomia,
·8
neural tube defects,
·9
neonatal hypoglycemia,
·10hypocalcemia,
·11hypomagnsemia,
·12hyperbilirubinemia,
·13birth
·14trauma,
·15prematurity syndromes, and
·16subsequent childhood and
·17adolescent obesity.
Prevalence
The prevalence of GDM
varies worldwide and among different racial and ethnic groups within a country.
National Diabetes
Data Group(NDDG) or of Carpenter and Coustan have found prevalence rates
of 1.4% to 12.3% in the United States, respectively.
Pathophysiology
Gestational diabetes is
pathophysiologically similar to type II diabetes.
Approximately 90% of the
persons identified have a deficiency of insulin receptors (prior to pregnancy)
or a marked increase in weight that has been placed on the abdominal region.
The other 10% have
deficient insulin
production and will proceed
to develop mature-onset insulin-dependent diabetes.
HPL blocks insulin
receptors and increases in direct linear relation to the length of pregnancy.
Insulin release is enhanced
in an attempt to maintain glucose homeostasis.
The patient experiences
increased hunger due to the excess insulin release as a result of elevated
glucose levels.
This insulin release
further decreases insulin receptors due to elevated hormonal levels.
Diagnostic Criteria and
Screening Procedures
The traditional method of
screening for GDM is to assess risk factors:
·18age,
·19prepregnancy weight,
·20family history of diabetes
in a first-degree relative,
·21previous large baby, and
·22previous perinatal loss.
Unfortunately, screening
based solely on risk factors will only identify approximately 50% of women
with GDM.
Glucosuria is a common finding in pregnancy
due to increased glomerular filtration and is therefore unreliable as a
diagnostic finding.
The ADA (American Diabetes
Association) recommend that all pregnant women, who have not been identified
with glucose intolerance earlier in pregnancy, be screened with a 50-g 1-hour
GCT between 24 and 28 weeks of pregnancy.
Such test can be performed
at anytime of the day and with disregard to previous meal ingestion.
A value equal to or above
140mg/dL should be used as the threshold level and indicates the need for a
100-g 3-hour OGTT. For the OGTT, the patient is fasting and receives 100-g of
glucose after a fasting glucose level is obtained.
A blood sample is taken
every hour for 3 hours. The patient is advised to sit quietly during the test
to minimize the impact of exercise on glucose levels.
Medical Management
The reason for lowering
the glucose level to a normoglycemic one is to prevent diabetic
complications.
The goal of medical
management of women with GDM, therefore, is to prevent perinatal
morbidity and mortality by normalizing the level of glycemia and
other metabolites(i.e., lipids and amino acids) to the levels of
nondiabetic pregnant individuals.
Dietary Therapy
Nutritional counseling is
the mainstay of therapy for the gestational diabetic woman.
The optimal dietary
prescription would be one that provides the calories and nutrients necessary
for maternal and
fetal health, results in
normoglycemia, prevents ketosis, and results in appropriate weight gain.
One of the difficulties
with dietary prescription for women with GDM is the difference between lean and
obese women.
Obese women with GDM may
benefit from a low calorie diet and weight reduction to reverse the metabolic
disturbances, but proper nutrition is needed to assure fetal growth and
development.
The patient checks her
glucose 4 times daily (e.g., fasting, and 1-hour postprandial breakfast, lunch,
dinner ).
The desired values are a
fasting of <90mg/dL and a 1-hour <130mg/dL.
The average glucose levels
should be~90. After she has obtained a good understanding of her diet and the
glucose values are in the
desired range, she can decrease the frequency of testing to 3 days per week chosen
randomly.
Insulin Therapy
If diet is not successful
in maintaining relative euglycemia, then insulin therapy is recommended.
To identify the women who
will require insulin, circulating glucose levels should be monitored at
frequent
intervals.
The ADA and ACOG (American
College of Obstetricians and Gynecologists ) recommend glucose measurements be
taken both fasting and after meals to 1 to 2-week intervals.
Insulin therapy should be
initiated if the fasting glucose levels exceed 105mg/dL and/or if the 2-hour
postprandial levels exceed 120mg/dL on two or more occasions within a 2-week
interval.
Several centers, however,
use the 1-hour time point because it reflects the peak glycemic response to a
meal.
Two studies have found that
the 1-hour postprandial glucose level was a better predictor of infant birth
weight than the fasting level. For this reason, when the fasting blood glucose
level is 90mg/dL or more, or the 1-hour postprandial glucose is 120mg/dL or
more on two or more glucose measurements within 1 or 2 weeks, then insulin
therapy is initiated.
Exercise Therapy
Cardiovascular conditioning
or aerobic exercise has both acute and long-term effects on insulin
sensitivity, insulin
secretion, and glucose metabolism. Because exercise is associated with a
decrease
in blood glucose
concentration both acutely and after a training program and exercise training
with
weight control or reduction
is associated with lower fasting and postprandial insulin concentrations
and apparent increases in
insulin sensitivity, regular exercise may be useful in the treatment or
prevention of GDM.
There are many other
potential benefits of exercise training and increased cardiorespiratory
fitness,
such as improvement in
cardiovascular risk factors and the prevention or reduction of cardiovascular
complications in people
with diabetes.
Recognizing the importance
of physical activity, the Third International Workshop-Conference on
Gestational Diabetes has
recommended exercise as a treatment modality for GDM in women who
do not have a medical or
obstetric contraindication for an exercise program.
Obstetric Management
Antepartum Care
Surveillance for fetal
well-being should begin between 28 and 32 weeks. Methods of fetal surveillance
may include fetal kick counts, the nonstress test(NST), the contraction stress
test (CST), and the biophysical profile.
Signs of fetal compromise
include the following:
·
decreased fetal movement,
·
a nonreactive NST,
·
a positive CST and
·
a poor biophysical profile.
The frequency and timing of
fetal surveillance depend on the severity of the disease and the degree of
glycemic control. Frequent ( every 4 to 6 weeks) ultrasound examinations to
assess fetal growth should be performed.
In the case of abnormal
fetal testing, the practioner should assess gestational age and, if the fetus
is found to be mature, should proceed to delivery.
If the fetus is
intermediate in maturity, amniotic fluid assessment for pulmonary maturity may
assist in the decision regarding whether delivery should be effected.
If the fetus is immature,
further testing such as contraction stress tests or hospitalization with
continuous fetal heart rate monitoring is advised.
Preterm labor is increased in patients
with diabetes and they should be treated with magnesium sulfate as the initial
tocolytic agent because the beta mimetics markedly influence glucose control.
Corticosteroids increase
maternal glucose levels, and this therapy may consist of continuous insulin
infusion in certain cases.
Intrapartum and Postpartum Management
Induction of labor is
recommended at 38 weeks in patients with poor glucose control and macrosomia.
Insulin-requiring diabetics
should be induced at 40 weeks’ gestation if spontaneous labor has not occurred.
Induction of labor may be
attempted if the fetus is not excessively large and if the cervix is capable of
being induced( i.e., if the cervix is soft, appreciably effaced, and somewhat
dilated).
The possibility of shoulder
dystocia in the macrosomic infant of a mother with diabetes must be considered;
cesarean section may be indicated to avoid the trauma of a delivering of a
large infant(>4000g). Euglycemia should be maintained during labor.
Prognosis
Women diagnosed with
gestational diabetes have an increased risk of developing diabetes mellitus in
the future.
If they require insulin for
their pregnancy, there is a 50% risk of diabetes within 5 years. If dietary
control has been sufficient, a 60% risk of developing diabetes mellitus within
10-15 years still
persists.
For this reason, all
gestationally diabetic patients should have a 75-g 3-hr glucose tolerance to
evaluate for preexisting diabetes.
If the 1-hr value is high,
it represents decreased insulin capacity, whereas an elevated 3-hr value
reflects decreased insulin receptors.
In the former, limiting
simple sugars in the diet should become a lifetime goal.
In the latter, weight loss
with increased abdominal musculature should significantly reduce the increased
risk of diabetes.
Questions
Question 1: The infant of a diabetic mother is NOT at
risk for which of the following?
(A) Increased perinatal death rate
(B) Hypocalcemia
(C) Hyperglycemia
(D) Neural tube defects
(E) Macrosomia
See answer 1
Question 2: Glucosuria in urine samples during
routine prenatal visits indicates:
(A) Gestational diabetes
(B) An increased glomerular filtration of glucose
(C) A need for dietary control
(D) A need for a 3-hour glucose tolerance test
(E) A need for small doses of insulin
See answer 2
Question 3: A 1-hour glucose tolerance test in a
woman with a previous stillborn infant resulted in the following value: 1-hour
blood sugar = 140mg/dL. Follow-up for this patient should include which of the
following?
(A) Nothing further
(B) A 2000-calorie diet
(C) Standard glucose tolerance test
(D) Home glucose urine testing
(E) A 2-hour postprandial blood sugar
See answer 3
Answer 1: C . The effects of diabetes on the fetus
and infant can be considerable, especially in uncontrolled diabetes. There is
an increase in fetal abnormalities such as neural tube defects.
Macrosomia is common, and the perinatal death rate
is higher than normal. The newborn may show hypocalcemia and hypoglycemia( not
hyperglycemia). The insulin secretion that has been stimulated in the fetus by
the high levels glucose from the mother continues after birth and can drop the
newborn
blood glucose to dangerously low levels.
Back to question 1
See text for more details
Answer 2: B. Glucosuria is most often secondary to
the pregnancy-related glomerular filtration of glucose without an increased
tubular reabsorption.
The finding of glucose in the urine of a pregnant
woman does not mean that she has gestational diabetes. However, it is an
indication to perform glucose testing because gestational diabetes is a
distinct possibility. The initial test would be a 1-hour screening test and not
the 3-hour test, which is only done if the 1-hour glucose tolerance test is
abnormal. It is unnecessary to control dietary glucose intake strictly without
a diagnosis of gestational diabetes. Likewise, small doses of insulin would be
unnecessary in the absence of a diagnosis of
diabetes.
Back to question 2
See text for more details
Answer 3: C . The screening 1-hour glucose
tolerance test was ordered because of the woman’s history of a stillborn
infant. In a woman with a history of unexplained fetal death, there should be a
high index of suspicion of diabetes. Although the 1-hour test result results
were abnormal, a diagnosis of gestational diabetes cannot be made on that value
alone; therefore, there is no immediate need for dietary control or
postprandial blood sugar monitoring. However, the abnormal 1-hour test results
should be followed up by a standard 3-hour glucose tolerance test. If two or
more of the four results are abnormal, the patient is diagnosed as having
gestational diabetes.
In addition, even if the patient is diagnosed as
diabetic, the degree of glucosuria in a patient with
diabetes does not reflect plasma glucose values.
Back to question 3
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