Gestational Diabetes

The following description of gestational diabetes is reprinted from The Brewer Medical Diet for Normal and High-Risk Pregnancy, by Gail Sforza Brewer [Krebs] with Thomas Brewer, M.D., published in 1983. While the standards recommended by the Diabetes Data Group may have been revised in more recent years to yet another, possibly even lower blood glucose level, which I will be researching in coming weeks, the principles advocated by Dr. Brewer in this reprint remain relevant.

For an additional source on gestational diabetes, please see "Gestational Diabetes: Myth or Metabolism?", by Joy Jones, RN, which has been reprinted at the end of this page.

For more information on testing for blood glucose and proper nutrition for apparently elevated blood glucose levels, please see Understanding Diagnostic Tests in the Childbearing Year, by Anne Frye, CPM, listed on our "Resources" page. Perhaps you can obtain a copy of that book from your local library, through inter-library loan

"Diabetes" (p. 211)

While there is general agreement among specialists about improving the outcome of pregnancy for the mother with insulin-dependent diabetes, controversy rages about class A diabetes, that is, "gestational diabetes"--irregularities in blood glucose levels that appear in an individual woman only during pregnancy. The problem stems, in our opinion, from a redefinition of what constitutes diabetes in pregnancy, formulated by the National Diabetes Data Group in 1979.

Prior to that time, a blood glucose level of 140-150 milligrams per milliliters of plasma after fasting for twelve hours--the level considered normal in the nonpregnant--was used as the upper range of normal in pregnancy, too. However, owing to new research conducted on pregnant women in which blood glucose levels were measured over the course of thousands of pregnancies, a new, much lower number--105 milligrams per milliliters was recommended as the upper limit of safety during pregnancy. And this is the number now being enforced by many doctors who give a great deal of attention to diabetes screening in their obstetrical practices.

The difficulty with the new research is that, like almost all other research conducted in pregnancy, no attempt was made to determine what is the normal blood glucose level in well-nourished subjects! That is, the research samples included large numbers of women who had never been advised what a proper diet consists of in pregnancy, much less been carefully evaluated for nutritional problems as pregnancy progressed. So, while 105 turns out to be the average number for all these women, it is highly likely that it is incorrect for the well-nourished. The reason: Well-nourished women who have adequate protein, calories, vitamins, and minerals keep their blood glucose levels normal and even maintain an energy supply reserve (glycogen) stored in their livers. This glycogen reserve is called upon to keep blood levels of glucose within normal ranges, should you go for a few hours without eating.

In the well-nourished woman, these glycogen stores are good for about twelve hours. But in the poorly or marginally nourished mother, the glycogen stores are minimal or even non-existent. So the blood level of glucose falls soon after eating and scrapes along until the next meal. We are certain that 105 milligrams per milliliter is an artificially low level for pregnancy blood glucose, a determination that was heavily weighted with results from women whose pregnancy diets simply were not adequate for the nutritional demands pregnancy imposes.

We are making a big point of this because of the intense anxiety produced in the mother who is told not only that she is diabetic, but that even with minor elevations of glucose she is likely to experience the full gamut of disastrous pregnancy outcomes associated with full-blown, out-of-control diabetes. Furthermore, as calls to our hotline indicate, many women are not being couseled properly about the dietary and exercise aspects of diabetes when their "gestational" diabetes (according to the new criteria) is diagnosed. Instead, they are hurried directly onto insulin therapy--and ordered to check their glucose levels at home every hour to keep it between 100 and 105!

All too often, the physician who has ordered this form of treatment also sends the mother home with one of the old, hazardous, restrictive diets or just tells her to "cut out all carbohydrates." Calls from all over the country indicate to us that this is not an isolated phenomenon, but a growing trend in diabetes management that bodes ill for the health of the many thousands of pregnant women who will be falsely diagnosed as diabetic and then be further mismanaged in terms of their nutritional needs.

You may find yourself in this predicament if:

you have a family history of diabetes that alerts your physician to the possibility that you, too, may be developing the disease even though there is no glucose spilling in your urine;

you have given birth previously to a baby who weighed more than 9 pounds (as happens commonly when your diet is excellent);

you are gaining more weight on a good diet than your doctor or midwife has been trained to think is acceptable (you may have twins, you may have been thin and underweight, you may be just perfect, but their weight limit is still back at 20 pounds, which was taught thirty years ago as the maximum acceptable weight gain--no matter what was happening!);

you have a sonogram for some other reason and it's determined that your baby is bigger than the charts say it should be for the length of your pregnancy (no account is taken of the fact that those charts are also heavily weighted with babies whose mothers were not optimally nourished!);

you have a normal (by the old standard) blood glucose level (140-150 mg. per ml.) discovered when you take a test for it at some point in pregnancy (to satisfy your doctor's insistence);

you spill some glucose in you urine, but upon further evaluation show no other sign of diabetes (pregnancy makes some women's kidneys ultrasensitive to glucose, so they allow some to escape--a condition call low renal threshold that is in no way related to diabetes and which is harmless).

If you and your doctor disagree on what is to be done about your pregnancy care, you may have to search for someone whose philosophy and practices are more in keeping with your own. Before taking any glucose tolerance tests, inquire about the doctor's proposed plan of therapy, should you turn up as a "gestational" diabetic, and ask what level of blood glucose the doctor uses to decide if you are well or not. If you don't like what you hear, call the medical school nearest you for referral to a diabetes specialist who might, at the very least, be able to send you reprints dealing with the dietary management aspect of your care that you could then bring in to the doctor on your next visit. Some physicians are open to discussion with their patients; others discharge you from their practice if they feel you are unwilling to comply with their way of doing things.

Regardless of what you decide to do, keep your nutritional needs clearly in mind and meet them every day. Our diet is well suited to the needs of the diabetic mother, with additional protein intake in the form of between-meal snacks to achieve the 1-gram-per-pound ratio that the best research advises.

The following has been reprinted from Mothering magazine, #50, Winter 1989. There will be an updated version of this article, in the same magazine, sometime in the next few months. Even 20 years later, the basic principles remain the same.

"Gestational Diabetes: Myth or Metabolism?" by Joy Jones, RN (p. 59)

With increasing frequency, birth practitioners are recommending glucose screening tests for pregnant women. They are telling women that the health of their pregnancies and the lives of their babies are in jeopardy if they refuse testing. As a result, many childbirth educators, birth practitioners, and pregnant parents are having to answer some probing questions: Do I really need this test? What can I do to pass the test? Could I take another test instead? Is there such a disease as "gestational diabetes"?

Several professional organizations have published testing guidelines. The American Diabetes Association recommends that all pregnant women take a one-hour glucose test.(1) The Centers for Disease Control advise that preferably all pregnant women, but definitely those with diabetic risk factors or over the age of 25, take a one-hour glucose test.(2) The American College of Obstetricians and Gynecologists recommends that women who have indications of diabetic risk or who are over the age of 30 have glucose screening.(3) The American College of Nurse Midwives has not yet published any guidelines [as of 1989], since research on the subject is still incomplete, and its members usually follow the protocols of their medical backup.

Not only do the guidelines vary, but the test results themselves are questionable. And yet these results can signify the difference between a low-tech or high-tech pregnancy and birth. Moreover, some birth practitioners do not feel that "gestational diabetes" is an illness requiring treatment. The controversial nature of "gestational diabetes" becomes clear when it is distinguished from the clinical picture of diabetes in individuals who are not pregnant.

Clinical Diabetes in Nonpregnant Populations

What happens when you eat carbohydrates and sugars? Enzymes convert the food into simple sugars, some of which are digested and used immediately and some of which are stored for future use. Glucose, the most important sugar, enters the tissue cells, where it combines with oxygen to form carbon dioxide and water. The energy released by this chemical reaction is used for muscular work and for maintaining bodily temperature. Insulin, a hormone secreted by the pancreas, promotes the transport of glucose across the cell wall.

Diabetes is often thought of simply as a lack of insulin. However, according to Foster in Harrison's Principles of Internal Medicine, the term diabetes can refer to many different syndromes.(4) The symptoms of diabetes mellitus, one of those syndromes, include the presence of sugar in the urine, excessive thirst, excessive urination, increased food intake, and an elevated plasma glucose (blood sugar) level. Diagnosis of diabetes mellitus is generally made on the basis of test results alone if the fasting plasma glucose levels are persistently elevated.

The symptoms of diabetes mellitus are associated with one of three major physiological conditions: a lack of insulin, an elevated production of glucose, or an insulin resistance. These conditions have several root causes [see chart]. A lack of insulin can be caused by viruses(5) or a diet high in unsaturated fatty acids, low in magnesium, and low in vitamin B-6, which can damage the pancreas enough to reduce insulin secretions.(6)

Elevated plasma glucose levels, or hyperglycemia, can be produced by an infection or the presence of epinephrine (adrenalin), estrogen, or steroids in the blood.(7) In response to the stress of infection, the body secretes epinephrine and cortisol. Epinephrine increases blood sugar by causing the liver to break down glycogen (a stored carbohydrate). Estrogen, progesterone, and lactogen may raise blood sugar by counteracting the action of insulin. Steroids stimulate the liver to form more glucose from proteins and fats.

The third condition, insulin resistance, can be caused by obesity, physical inactivity, or food deficiency (especially carbohydrate deficiency). Obesity reduces the relative number of insulin receptors, which are needed in the transport of insulin across the cell wall.(8) Physical inactivity or insufficient food can cause a decreased carbohydrate tolerance, which in turn leads to insulin resistance.(9) In extremely rare cases, insulin resistance is due to the secretion of unusual types of insulin.(10)

In addition, genetic factors can predispose the body to react to any of the above influences with symptoms of diabetes.(11) In such instances, as well as in some of the above situations, an individual with normal test results may be "considered a potential diabetic because of lifestyle, physical history, or family history."(12)

"Gestational Diabetes"

In "gestational diabetes"--also known as Class A, latent, chemical, or preclinical diabetes--a pregnant woman having no symptoms of diabetes has test results similar to those of nonpregnant diabetics. By definition, this "diabetes" ceases once the pregnancy is over. Clinical diabetes that is diagnosed prenatally and persists beyond the pregnancy is not properly called "gestational diabetes." [see sidebar]

Many birth practitioners question the existence of "gestational diabetes" because it is often diagnosed solely on the basis of a response to a test. Why would a nonsymptomatic mother show elevated blood sugar levels? Perhaps her body is reflecting the chemical gymnastics imposed by the test itself--which may involve fasting followed by the consumption of large doses of concentrated glucose. Or perhaps her body is registering a healthy response to the inherent dynamics of pregnancy.

Blood sugar elevations during pregnancy can result from several factors. Any of the root causes of clinical diabetes mentioned earlier may be operative. Another possibility is that the placenta secretes lactogen, estrogen, and progesterone--hormones that counteract the function of insulin--as well as potent enzymes that destroy insulin.(13) Would the placenta, an organ designed to sustain a pregnancy and nourish a baby for nine months, consistently make this "mistake"?

It is important to understand that the body handles glucose differently during pregnancy. In Birthrights, Sally Inch explains one reason for the pregnant body's need for "hyperglycemia" (higher blood sugars): "Instead of being rapidly converted to glycogen and stored in the liver for future use, the glucose remains for longer periods in the [woman's] bloodstream so that her developing baby has an easily available source of energy that can be used for growth and storage as fat (+glycogen)."(14)

Tom Brewer, MD, has found that well-nourished pregnant women can maintain rather stable plasma glucose levels and adequate glycogen stores in the liver, whereas poorly or marginally nourished women have minimal or nonexistent glycogen stores. In such instances, the plasma glucose level "falls soon after eating and scrapes along until the next meal."(15) If today's pregnancy standards have been set by research conducted on undernourished women--a likely assumption, based on several decades of recommended weight restriction--then low blood sugar levels may appear to be the norm. However, it may be truly normal to maintain higher levels than current standards allow for.(16)

Another normal occurrence in pregnancy is a lowered renal threshold for glucose and other sugars. On the average, the kidneys filter 170 liters of filtrate out of the blood daily. Only 1 to 1 1/2 liters are eliminated as urine, whereas about 108 liters are absorbed into the bloodstream for bodily use. Some of the substances reabsorbed have a well-defined reabsorption limit, or "renal threshold."(17) During pregnancy, the renal threshold for sugar changes, and glucose is excreted in the urine at a lower blood plasma (liquid portion of the blood) levels.

There is a good reason for a lowered renal threshold for glucose during pregnancy. If a woman is eating well, her blood volume increases by 40 to 60 percent. (If a woman is not eating well, her blood volume may decrease.) As a result, the amount of blood flowing through the kidneys and the rate at which fluid passes from the blood through capillary walls in the kidneys increas by about 40-60 percent. At the same time, the reabsorption rate of the filtrate into the blood remains the same or decreases.(18)

Since the reabsorption rate does not keep up with the filtration rate, some substances do not get reabsorbed as efficiently as in nonpregnancy. For instance, in nonpregnancy, the kidney will continue to reabsorb glucose until blood sugar levels reach about 170 mg/100 ml., when the kidney will begin excreting glucose with the urine; during pregnancy, however, the kidney may stop reabsorbing glucose at a much lower blood sugar level (100 mg/100 ml), and sugar may show up in the urine even though glucose levels in the blood are normal.

Finding sugar in the urine at a prenatal visit usually does not mean that plasma glucose levels are higher than is healthy. According to William's Obstetrics, about one-sixth of all pregnant women spill glucose in the urine.(19) Evelyn Burns, in "Diabetes Mellitus and Pregnancy," reports that glucose in the urine occurs in 50 percent of all normal pregnancies.(20)

Testing Options

A birth practitioner who does not believe that some glycosuria (the presence of glucose in the urine) is normal in pregnancy or who wishes to rule out other symptoms suggestive of clinical diabetes will recommend prenatal testing. Typical options include a fasting blood sugar test, a one-hour glucose test, a two-hour postprandial blood sugar test, a random blood sugar test, a hemoglobin A1C test, and a glucose tolerance test (GTT). Some practitioners consider the two-hour postprandial and random blood sugar tests to be nonstandardized (not uniformly analyzed) and prefer not to use them.

The fasting blood sugar test requires an eight- to 12-hour fast, after which a sample of blood is drawn to determine the fasting blood sugar level. Normal values range from <105 mg/100 ml to <150 mg/100 ml, depending on the philosophy of the birth practitioner. (Note: "<" means "less than.")

The one-hour glucose test requires an eight- to 12-hour fast, after which a preliminary sample of blood is drawn. The mother is then given 50 grams (the equivalent of 2 ounces) of glucose, in the form of a "glucola" drink; one hour later, a second sample is drawn to determine the level of glucose present. "In general, the upper limit of normalcy increases with age and during pregnancy."(21)

An interesting variation of this test appears in the winter 1987 issue of Midwifery Today. Here, the one-hour glucose test is conducted at 24 to 28 weeks gestation, and the mother does not fast for the test. A value of 140 mg/100 ml or higher suggests "gestational diabetes." Also included is a recipe for a homemade glucose concentrate to be given during the procedure.

A major problem with both standardized tests is the long period of fasting that is required.(22) Even a well-nourished pregnant woman depletes the glycogen supplies in her liver after 12 hours of fasting. (An under-nourished woman may deplete her glycogen stores soon after each meal is digested.) This depletion causes the nausea that many women experience after eight to 12 hours without food. Ideally, pregnant women should eat something every two to three hours around the clock.

Fasting during pregnancy creates problems on the metabolic level as well. When blood sugar levels are low, the body restores them by breaking down reserves of fat. "The continued demand for glucose and amino acids for fetal anabolism [tissue building] causes a state of 'accelerated starvation.' Lypolysis [fat breakdown] to mobilize fat as metabolic fuel occurs more rapidly during pregnancy."(23) As a result, blood levels of ketones (by-products of fat breakdown) rise. After repeated episodes of high ketone levels over a period of several days or weeks, especially in the first trimester, impaired intellectual performance, developmental abnormalities, or fetal death can occur.(24) The postprandial, random blood sugar, or hemoglobin A1C tests may be better alternatives than those with extensive fasting requirements.

The two-hour postprandial test requires blood sampling two hours after a meal has been eaten. The mother should be encouraged to eat a "generous breakfast in which carbohydrates are well supplied, such as pancakes, with syrup, sausages, and a large glass of orange juice."(25) Normal test values range from <120 mg/100 ml to <140 mg/100 ml.(26) (One obstetrician in the Chicago area accepts an upper limit of 170 mg/100 ml.) Postprandial guidelines often suggest glucola in lieu of a generous breakfast; however, eating a meal is a healthier option.

The random blood sugar test evaluates blood that is drawn at a random time of day. Fasting is not necessary, and only one blood sample is needed. The upper range of normal varies from about 100 mg/100 ml to 110 mg/100 ml. Test results for women on the high-protein Brewer diet [see For More Information] and women who eat several snacks between meals tend to be slightly higher than those for mothers who eat only three meals a day.

The hemoglobin A1C test also does not require fasting. It analyzes glucose levels over the previous 120 days (the life span of a red blood cell), and results are not influenced by food eaten in the hours before the blood is drawn. A1C is a type of hemoglobin that absorbs glucose; a large percentage of saturated hemoglobin may indicate high blood sugar levels. Only one blood sample is drawn, and the normal values range from 4 to 7 percent of total hemoglobin.

The glucose tolerance test (GTT) is often considered the most definitive procedure for determining whether or not glucose is being properly managed. The GTT requires an eight- to 12-hour fast, after which the first blood sample is taken to determine a fasting glucose level. Then the woman drinks 50 to 100 grams (2 to 4 ounces) of concentrated glucose (glucola), and blood and urine samples are taken at half-hour (sometimes omitted), one-hour, two-hour, and three-hour intervals. Infrequently, a five-hour sample is taken. The normal blood plasma values for the three-hour GTT are as follows: fasting-- <105 mg/100 ml; half-hour-- <200 mg/100 ml; one hour-- <190 mg/100 ml; two hours-- <165 mg/100 ml; and three hours-- <145 mg/100 ml. Normal values are lower when whole blood is tested.(27)

Because of the widespread use of the GTT, it is important to be aware its drawbacks. First, the mother is required to fast for eight to 12 hours before being tested. Secondly, several factors can lead to false-positive results: "It is mandatory that the patient be on a preparatory diet containing 250 to 300 g carbohydrate for three days before testing; otherwise a decreased carbohydrate tolerance may be observed, known as starvation diabetes. Physical inactivity also decreases carbohydrate tolerance, and therefore prolonged bedrest may give false-positive results."(28) Women taking the GTT or the one-hour glucose test are advised to take a long walk--from 1 to 3 miles--between ingesting the glucose and having each blood sample drawn, as this will tend to lower the blood sugar levels. And thirdly, the GTT floods the mother and baby with high levels of concertrated glucose. The effects of glucose flooding, particularly after several hours of fasting, are unknown.

Finally, one of the greatest problems with the GTT is its inaccuracy. Influences such as diet, age, stress, fever, infection, overwork, lack of exercise, illness, and worry can easily cause unreliable results. Even anxiety about the needles or about the the consequences of test results can provoke a flood of epinephrine, which in turn releases glucose and blocks insulin release, resulting in unusually high recordings of glucose levels.(29)

How accurate can the GTT be, and how accurate is it? Dr. Edward Pinckney writes in Dissent in Medicine that an excellent test is right at least 97 percent of the time, and any test that is less than 80 percent accurate should not be undertaken until its potential benefits are shown to outweigh its known risks.(30) According to Foster in Harrison's Principles of Internal Medicine, 75 percent of clients shown by the GTT to have "impaired glucose tolerance" (a possible tendency for diabetes) never actually develop diabetes.(31) The implication is that positive GTT results are accurate only 25 percent of the time.

How reliable is prenatal diabetic evaluation? In 1979, the National Diabetes Data Group lowered the commonly accepted standards for normal glucose levels in pregnancy. The upper limit for the fasting glucose test dropped to 105 mg/100 ml from the previously accepted level of 140 mg/100 ml. The upper limit for the two-hour postprandial test dropped to 120 mg/100 ml from 150 mg/100 ml.(32) Consequently, many well-nourished women with normal plasma glucose levels before 1979 would now be considered to have abnormal glucose levels and would be diagnosed as having "gestational diabetes."

Diagnostic Objections and Complications

The diagnosis and treatment of "gestational diabetes" elicits four major objections for birthing reform advocates.

Is "gestational diabetes" a defect in metabolism or a myth borne out of a misunderstanding of normal pregnancy? The definitive answer is not in yet. Unfortunately, as Elizabeth Noble says, "a great many people share the medical establishment's mechanistic view that control of nature is good and that progress is only a matter of more--more pills, more techniques, more information."(34)

It is unrealistic and unreasonable to routinely screen the entire pregnant population for diabetic tendencies. According to Tom Brewer, no study in any of the medical literature indicates adverse effects from "gestational diabetes." The effects that are usually referred to, he says, are found in poorly nourished women with poorly controlled "real" (clinical) diabetes. It is quite possible that "gestational diabetes" in the well-nourished woman is simply evidence of her body trying to do its job of growing and birthing a healthy baby.