Gestational diabetes (GDM) is a
condition in which women without previously diagnosed diabetes
exhibit high blood glucose levels during pregnancy.
Gestational diabetes generally
has few symptoms
and it is most commonly diagnosed by screening
during pregnancy. Diagnostic tests detect inappropriately high levels of glucose
in blood samples. Gestational diabetes affects 3-10% of pregnancies. No
specific cause has been identified, but it is believed that the hormones
produced during pregnancy increase a woman's resistance to insulin,
resulting in impaired glucose tolerance.
Babies born to mothers with
gestational diabetes are at increased risk of problems typically such as being large for
gestastional age (which may lead to delivery complications), low blood
sugar, and jaundice. Gestational diabetes is a treatable condition and
women who have adequate control of glucose levels can effectively
decrease these risks.
Women with gestational diabetes are at increased risk of
developing type 2 diabetes mellitus after pregnancy,
while their offspring are prone to developing childhood
obesity, with type 2 diabetes later in life. Most patients
are treated only with diet modification and moderate exercise but some take anti-diabetic drugs, including insulin.
RISK FACTORS
§
Previous
diagnosis of gestational diabetes or prediabetes, impaired glucose tolerance, or impaired fasting glycaemia
§
Maternal age - a woman's risk factor increases
as she gets older (especially for women over 35 years of age)
§
Ethnic background (those with higher risk
factors include African-Americans, Afro-Caribbeans,
Native Americans, Hispanics,
Pacific Islanders, and people originating from
the Indian subcontinent)
§
A previous pregnancy which resulted in a child
with a high birth weight (>90th centile, or >4000g
§
Previous poor obstetric history
PATHOPHYSIOLOGY
§
The precise mechanisms underlying gestational
diabetes remain unknown. The main cause of GDM is increased insulin resistance.
§
Pregnancy hormones and other factors are thought
to interfere with the action of insulin as it binds to the insulin
receptor. The interference probably occurs at the level of the cell
signaling pathway behind the insulin receptor.
§
Since insulin promotes the entry of glucose into
most cells, insulin resistance prevents glucose from entering the cells
properly. As a result, glucose remains in the bloodstream, where glucose levels
rise.
§
More insulin is needed to overcome this
resistance; about 1.5-2.5 times more insulin is produced than in a normal
pregnancy.
§
Insulin resistance is a normal phenomenon
emerging in the second trimester of pregnancy, which progresses thereafter. It
is thought to secure glucose supply to the growing fetus.
§
Placental hormones, and to a lesser extent increased fat deposits during
pregnancy, seem to mediate insulin resistance during pregnancy. Cortisol
and progesterone
are the main culprits, but human placental lactogen, prolactin
and estradiol
contribute too.
§
Because glucose travels across the placenta, the
fetus is exposed to higher glucose levels. This leads to increased fetal levels
of insulin
(Hyperinsulinemia).
§
The growth-stimulating effects of insulin can
lead to excessive growth and a large body (macrosomia).
§
After birth, the high glucose environment
disappears, leaving these newborns with ongoing high insulin production and
susceptibility to low blood glucose levels (hypoglycemia)
DIAGNOSIS
§ Blood
glucose testing : A fasting plasma glucose level >125mg/dL
or a casual plasma glucose >200 mg/dL meets the threshold for the diagnosis
of diabetes.
Fasting and 2 hours
postprandial venous plasma sugar during pregnancy.
Fasting
|
2h Postprandial
|
Result
|
<100 mg/dl
|
< 145mg/ dl
|
Not diabetic
|
>125 mg/ dl
|
>200 mg/ dl
|
Diabetic
|
100-125 mg/dl
|
125-200 mg/dl
|
Border line indicates glucose
tolerance test.
|
Oral Glucose Challenge Test:
§ Also called the O'Sullivan test.
§ It is performed between 24–28 weeks, and
can be seen as a simplified version of the oral glucose tolerance test (OGTT).
§ It involves drinking a solution containing
50 grams of glucose, and measuring blood levels 1 hour later.
§
A plasma value above 130-140mg/dl one hour after
is commonly used as a threshold for performing a 3-hour OGTT.
Oral Glucose Tolerance Test (OGTT)
Prerequisites: - Normal diet for 3 days before the test.
- No diuretics 10 days before.
- At least 10 hours fast.
- Test is done in the morning at rest.
Procedure: Giving 75
gm (100 gm by other authors) glucose in 250 ml water orally
Criteria for glucose tolerance test: The following are the
values which the American Diabetes Association considers to
be abnormal during the 100 g of
glucose OGTT:
- Fasting blood glucose level ≥95 mg/dl
- 1 hour blood glucose level ≥180 mg/dl
- 2 hour blood glucose level ≥155 mg/dl
- 3 hour blood glucose level ≥140 mg/dl
If any 2 or more of these values are elevated, the patient is considered
to have an impaired glucose tolerance test.
Glycosylated haemoglobin (Hb A1(
§
It is normally accounts for 5-6% of the total
haemoglobin mass. A value over 10% indicates poor diabetes control in the
previous 4-8 weeks.
§
If this is detected early in pregnancy, there is
a high risk of congenital anomalies .
§
If this is detected in late pregnancy it
indicates increased incidence of macrosomia and neonatal morbidity and
mortality.
§
The mean glucose represented by the hemoglobin
A1c level can be calculated using the "rule of 8's." A value of 8
percent equals 180 mg/dl, and each 1 percent increase or decrease represents ±
30 mg/dl.
§
Assessment for asymmetric fetal growth by
ultrasonography, particularly in early third trimester, may aid in identifying
fetuses that can benefit from maternal insulin therapy
§ Maternal
surveillance should include blood pressure and urine protein monitoring to
detect hypertensive disorders.
MANAGEMENT
Medical nutrition therapy should include the provision of adequate
calories and nutrients to meet the needs of pregnancy and should be consistent
with the maternal blood glucose goals that have been established. Noncaloric
sweeteners may be used in moderation.
Diet therapy is critical to successful regulation of maternal
diabetes. A program consisting of three meals and several snacks is used for
most patients. Dietary composition should be :
ü50
-60% carbohydrate,
ü20%
protein,
ü25-30% fat with
less than 10% saturated fats, up to 10% polyunsaturated fatty acids, and the
remainder derived from monosaturated sources
Insulin Therapy
Insulin therapy is recommended
when medical nutrition therapy fails to maintain self-monitored glucose at the
following levels:
- Fasting plasma glucose <105 mg/dL
- 1-hour postprandial plasma glucose <155
mg/dL
- 2-hour postprandial plasma glucose <135
mg/dL
Goal of Insulin Therapy
Self-blood glucose monitoring
combined with aggressive insulin therapy has made the maintenance of maternal
normoglycemia (fasting and premeal glucose between 50-80mg/dl and 1 hour
postprandial glucose <140mg/dl)
Twice daily ( before breakfast
and before dinner) injections of a combination of short and intermediate acting
insulins are usually sufficient to control most patients otherwise a
subcutaneous insulin pump is used.
The total first dose of insulin
is calculated according to the patient’s weight as follow:
In the first trimester
.......... weight x 0.7
In the second
trimester........ weight x 0.8
In the third trimester...........
weight x 0.9
If the total dose of
insulin is less than 50 units/ day, it is given in a single morning
dose with the ratio: Short acting (regular or Actrapid)/Intermediate (NPH or
Monotard) = 1 : 2
In higher doses, As
a general rule, the amount of intermediate-acting insulin will exceed the
short-acting component by a 2:1 ratio. Patients usually receive two thirds
their total dose with breakfast and the remaining third in the evening as a
combined dose with dinner
Insulin Dose adjustment
§
Home glucose monitoring with a reflectance meter
by measuring fasting and preprandial glucose values 4 times a day (30-40
min)before each meal.
§ All
values are recorded in a daily log.
§ In
patients who are not well controlled, a brief period of hospitalization is
often necessary for the initiation of therapy. Individual adjustments to the
regimens implemented can then be made.
KETOACIDOSIS
§
As pregnancy is a state of relative insulin
resistance marked by enhanced lipolysis and ketogenesis, diabetic ketoacidosis
may develop in a pregnant woman with glucose levels barely exceeding 200 mg/dl
.
§ Thus,
DKA may be diagnosed during pregnancy with minimal hyperglycemia accompanied by
a fall in plasma bicarbonate and a pH value less than 7.30.
§
Clinical signs of volume depletion follow the
symptoms of hyperglycemia, which include
o
Polydipsia and polyuria.
o
Malaise.
o
Headache.
o
Nausea/ Vomiting.
§
Occasionally, diabetic ketoacidosis may present
in an undiagnosed diabetic woman receiving β-mimetic agents to arrest preterm
labor.
§
Because of the risk of hyperglycemia and
diabetic ketoacidosis in diabetic women . Terbutaline and magnesium sulfate has
become the preferred tocolytic for cases of preterm labor in these cases.
§ Sometimes
Administration of antenatal corticosteroids to accelerate fetal lung maturation
can cause significant maternal hyperglycemia and precipitate DKA. In diabetic
patients.
§ An
intravenous insulin infusion will usually be required and is adjusted on the
basis of frequent capillary glucose measurements.
§ Meticulous
correction of metabolic and fluid abnormalities.
§ Every
effort should therefore be made to correct maternal condition before
intervening and delivering a preterm infant.
ANTEPARTUM FETAL EVALUATION
Antepartum fetal monitoring tests are
now used primarily to avoid unnecessary premature intervention allowing the
fetus to benefit from further maturation in utero.
Ultrasound
- Ultrasound is a valuable tool in evaluating fetal
growth, estimating fetal weight, and detecting hydramnios and
malformations.
- Maternal serum α-fetoprotein (MSAFP) at 16 weeks'
gestation is often used in association with a detailed ultrasound study
during the second trimester in an attempt to detect neural tube defects
and other anomalies. Normal values of MSAFP for diabetic women are lower
than in the nondiabetic population .
- Ultrasound examinations should be repeated at 4- to
6-week intervals to assess fetal growth. The detection of fetal
macrosomia, the leading risk factor for shoulder dystocia, is important in
the selection of patients who are best delivered by cesarean section.
Maternal assessment of fetal activity
- Maternal hypoglycemia, while generally believed to be
associated with decreased fetal movement, may actually stimulate fetal
activity.
The Non Stress Test (NST(
- Done weekly at 28 weeks and Twice weekly at 34 weeks
- Remains the preferred method to assess antepartum
fetal well-being in the patient with diabetes mellitus
- If the NST is nonreactive, a biophysical profile
(BPP) or contraction stress test is then performed .
Doppler Umbilical Artery Velocimetry
- Doppler umbilical artery velocimetry has been
proposed as a clinical tool for antepartum fetal surveillance in
pregnancies at risk for placental vascular disease.
- It is found that Doppler studies of the umbilical artery may be predictive of fetal outcome in diabetic pregnancies complicated by vascular disease.
- Elevated placental resistance as evidenced by an
increased systolic/diastolic ratio is associated with fetal growth
restriction and preeclampsia in these high-risk patients.
TIMING AND MODE OF
DELIVERY
- There is very
little evidence to support either elective delivery or expectant
management at term in pregnant women with insulin-requiring diabetes.
- When antepartum testing suggests fetal compromise,
delivery must be considered.
- Delivery by cesarean section usually is favored when
fetal distress has been suggested by antepartum heart rate monitoring.
- If a patient reaches 38 weeks' gestation with a
mature fetal lung profile and is at significant risk for intrauterine
demise because of poor control or a history of a prior stillbirth, an
elective delivery is planned.
- During labor, continuous fetal heart rate monitoring
is mandatory. Labor is allowed to progress as long as normal rates of
cervical dilatation and descent are documented.
- Arrest of dilatation or descent despite adequate
labor should alert the physician to the possibility of cephalopelvic
disproportion.
INSULIN MANAGEMENT DURING LABOUR AND DELIVERY
- Usual dose of intermediate-acting insulin is given at
bedtime.
- Morning dose of insulin is withheld.
- Intravenous infusion of normal saline is begun.
- Once active labor begins or glucose levels fall below
70 mg/dl, the infusion is changed from saline to 5% dextrose and delivered
at a rate of 2.5 mg/kg/min.
- Glucose levels are checked hourly using a portable
meter allowing for adjustment in the infusion rate.
- Regular (short-acting) insulin in administered by
intravenous infusion if glucose levels exceed 140 mg/dl.