Gestational Diabetes Mellitus

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

§  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)

§  Ethnic background (those with higher risk factors include African-Americans, Afro-Caribbeans, Native Americans, Hispanics, Pacific Islanders, and people originating from the Indian subcontinent)

§  Being overweight, obese or severely obese increases the

§  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.