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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Diabetes In Pregnancy Series
Sponsored by The Indian Health Service Clinical Support Center
PART 1: Screening and Diagnosis
4. Screening
Case Continued
Mrs. Kanulie's initial exam reveals a weight of 187 pounds (85 kg) and a height of 60 inches (152 cm). She is normotensive and there is no evidence of retinopathy. Her fundal height is 26 cm and fetal heart tones are normal. Her routine prenatal lab work is unremarkable. Her serum creatinine is 0.7 mg/dL and she has no proteinuria. A one-hour post-50 g glucose screen test (GST) returns with a plasma glucose of 186 mg/dL.
Patients with known pre-gestational diabetes do not need glucose challenge testing during pregnancy. A management plan can be made for them directly. High-risk patients such as our case patient should be screened at their initial visit. Most of the patients that have abnormal glucose tolerance testing in the early trimester are probably undiagnosed pre-gestational diabetics.
If early pregnancy screening is negative in high-risk patients, the screen should be repeated at 24-28 weeks. This timeframe has been chosen because it is thought to represent the time when the diabetogenic hormonal alterations of pregnancy are maximally operative, but still provides sufficient opportunity to implement interventions that may be beneficial as regards fetal growth. Some have also suggested re-screening those with risk factors at 32 weeks, thereby increasing the yield of the diagnosis of GDM. Screening may be repeated at 32 weeks, especially if there was one abnormal value on 3 hour 100g OGTT. (Neiger et al)
Screening is accomplished with a random (fasting not necessary) 50 g glucose challenge, followed by a venous (not finger-stick) glucose 1 hour later. Values > or = 140 mg/dL are considered positive. Sensitivity of the test is increased if > or = 130 mg/dL is used as the threshold, but of course more false positives result, and opinions remain divided as to the utility of the lower cut-off.
What about screening glucose levels of >185 mg/dL or > 200 mg/dL?
Landy et al suggested that a 3 hour 100 g oral glucose tolerance test (OGTT) was not necessary if the 1-hour 50-g glucose screening test (GST) was over 185 mg/dL. Upon further review, as well as, the work of Atilano et al and Shivvers et al, it appears that a 50-g screening test result > or = 200 mg/dL is not diagnostic of gestational diabetes. Nearly one of five such women had a normal three-hour oral GTT. Over-diagnosis of gestational diabetes may lead to unnecessary pregnancy surveillance and intervention in that pregnancy and thereafter.
Naylor et al found that the diagnosis of GDM alone is associated with inexplicable elevated risk of cesarean delivery with no improvement in outcome. In addition, there will be a proscribed series of unnecessary blood tests and subsequent interventions-both short term and long term. It is better to actually perform a 3 hr OGTT, rather than misdiagnosing in the range of 1-2 out of 5 patients.
Some providers were concerned may iatrogenically push these women over into diabetic ketoacidosis (DKA) with a 100-gm load test. This possibility was not verified in a PubMed literature search. That is not surprising, considering that an OGTT represents only part of one of the many soft drinks many patients drink several times a day. The only DKA found was in GDM patients who were given bursts of steroids or ritodrine and who developed DKA while on tocolysis. Another DKA scenario was: "Nausea, vomiting, and decreased caloric intake in an otherwise normal pregnant, diabetic woman requires evaluation to exclude ketosis".
A viable alternative in Native Americans, in accordance with a 1993 ACOG subcommittee, is to perform one step diagnostic testing. In tribes with high prevalence of diabetes, one can use a 3 hour 100-g OGTT as a one step screening / diagnostic method. Pettitt et al 1994 in a small study in the Pima successfully used a one-step 2 hour 75-g OGTT using WHO criteria.
Can we proceed directly to one step screening / diagnosis in AI / AN women?
Yes
Some providers have noted that many AI/AN patients are lost to follow-up between a positive glucose screen test result and the performance of the definitive diagnostic test, the 3 hour oral glucose tolerance test.
Other providers noted that many AI/AN women live in remote areas with limited access to care, yet have some of the highest rates of diabetes in pregnancy in the U.S., and possibly the highest in the world.
ACOG and the Indian Health system convened an Expert Panel of 35 experts on April 12, 1993 to discuss these and other issues related to the diagnosis of gestational diabetes mellitus in pregnancy. One of the main areas of discussion was that eliminating the screening phase and proceeding directly to a diagnostic test seemed warranted in certain AI/AN populations.
There was general concurrence that these rates were so high that being an AI/AN woman was sufficient to serve in itself as a positive screen, and thus to indicate the need for a diagnostic level of testing directly.
The Expert Panel suggested that upcoming Technical Bulletins (subsequently modified to 'Practice Bulletins') reflect that other loading doses are currently used in other populations.
Hence, the current ACOG Practice Bulletin, No. 30 now states.
"...there may be groups of individuals at such high risk for GDM that it may be more convenient and cost-effective to proceed directly to the diagnostic GTT without obtaining the laboratory screening test..."
Copies of the full 1993 Proceedings can be obtained from Elaine Locke, ACOG, or Neil Murphy, M.D., OB/GYN Chief Clinical Consultant, IHS.
Subsequently the American Diabetes Association issued this statement in Diagnosis and Classification of Diabetes Mellitus Diabetes Care 29:S43-S48, 2006
"One-step approach.
Perform a diagnostic OGTT without prior plasma or serum glucose screening. The one-step approach may be cost-effective in high-risk patients or populations (e.g., some Native-American groups). "
Should we screen for GDM at all?
Having said all that, the Society of Obstetricians and Gynaecologists of Canada (SOGC) reports that some have made valid arguments not to screen for GDM until a definitive randomized trial shows that screening actually improves patient outcomes. The SOGC Clinical Practice Guidelines, No. 121, November 2002 (Berger et al) provide an excellent discussion of what evidence is available, or for the most part lacking, to correlate milder degrees of glucose intolerance and patient outcomes. This confirmed previous Canadian SOGC analysis which suggested that suggestions for screening are currently based on consensus, rather than good evidence. (Meltzer et al)
There is one such trial underway, the Hyperglycemia and Adverse Outcomes (HAPO) study (password required to enter site). This large (n = 25,000) prospective study on GDM worldwide will study outcomes in relation to a 75 gram OGTT will be ready in 2003. Funded by the US National Institutes of Health, the HAPO study will involve 16 centers, 3 continents, and 25,000 unselected pregnant patients that will undergo a 75-gram oral glucose test at 28 weeks gestation. Only women who fulfill the WHO criteria for diabetes will be treated, so all lesser degrees of hyperglycemia can be correlated with short-term variables of pregnancy outcome. Follow-up studies will allow the examination of medium term and long term effects of maternal hyperglycemia on the future health of mother and her child. Only after this study will the threshold of maternal blood glucose concentration that carries no added risk to pregnancy be known.
Until the HAPO study is reported no significant attempt should be made to re-write existing screening methods. (Dornhorst et al) At this time American Indian and Alaska Native women should be considered high risk for GDM and screened as outlined in the ANMC Diabetes in Pregnancy Guidelines*.
