Acrobat
MS Word
PowerPoint
Volume 5, No. 6, June/July 2007
Abstract of the Month
A new management category: 'First Trimester GDM'
Here is a common question: Does my patient have gestational diabetes or did she have previously undiagnosed diabetes?
Your patient just came in for a prenatal visit in the first trimester. She has risk factors for diabetes in pregnancy, e. g., previous macrosomic infant, previous GDM, etc… (see other risk factors below*). As per your facility’s guidelines, you obtain an initial diabetes screen. The subsequent 3 hour 100 g OGTT also comes back abnormal. You manage her pregnancy as a previously undiagnosed diabetic patient. After pregnancy her follow-up 2 hour 75 g OGTT is normal. Did your patient really have pre-existing diabetes or just gestational diabetes? The answer is important to know because it has long term implications for her entire lifetime.
Background
In our Native American/Alaska Native pregnant populations, where diabetes mellitus is so common, it is often difficult to decide if a pregnant woman has gestational diabetes mellitus (GDM), or type 2 pre-gestational diabetes mellitus (PGDM) e.g., pre-existing DM. While the usual GDM screen is 24-28 weeks, many service units screen women at their first prenatal visit. This is probably more common if the woman has other risk factors besides her ethnicity.
What are the pros and cons of making the diagnosis early?
How do we decide if our client was actually diabetic between pregnancies?
Consider this case:
A 34 y/o Native American G4P3 presents for her first prenatal visit at 10 weeks by dates. Her BMI is 34.7 kg/M2. Her three prior children all weighed over 9 pounds, but her deliveries were uncomplicated. She thinks she may have been told she had GDM with her last pregnancy, but never followed up after the baby was born. Her mother is a type 2 diabetic, as are several other family members. She admits to being thirsty a lot, but she doesn’t have to get up at night to go to the bathroom more than once.
Should she be screened now for GDM?
Might she have undiagnosed PGDM?
This is more than a matter of semantics. How we decide on a specific diagnosis has long term health implications for the individual involved. A review of the definitions is probably in order at this point. Using the American Diabetes Association (ADA) definition, “A fasting plasma glucose level >126 mg/dL (7.0 mmol/L), or a casual plasma glucose level >200 mg/dL (11.1 mmol/L), meets the threshold for the diagnosis of diabetes, if confirmed on a subsequent day, and precludes the need for any glucose challenge.” The woman who meets those criteria quite clearly has PGDM. Likewise, the woman with a history of type 2 diabetes between pregnancies, on medical therapy, is easy to classify.
Women with type 1 diabetes are also usually quite obvious by history. But how about the pregnant woman found to have two fasting glucose values >100 mg/dL?
Or two post prandial values >140 mg/dL? Are such women “pre-diabetic”, or “gestational diabetics” or “PGDM”?
Do they need any further glucose challenge now during early pregnancy?
The effects of pregnancy on glucose metabolism
Here is why first trimester glucose results can be confusing. Evolution has set up the physiology of pregnancy to provide maximum substrate for the survival and development of the fetus. Post prandial glucose, fatty acid, and amino acid excursions are higher, thus readily enabling the fetus to siphon off maternal nutrients for its needs. This occurs, in the case of glucose, by active diffusion across the placental membrane. Nevertheless, especially during early pregnancy, a state of relative maternal hypoglycemia is customarily observed, especially in the pre-prandial state. In addition, the nausea and vomiting provoked by high human chorionic gonadotrophin levels leads to maternal catabolic state.
This situation may complicate the diagnosis of diabetes by the usual criteria. In the first trimester, fasting glucose are expected to be lower, and post prandial glucose values may or may not yet be elevated. Every woman may occupy somewhat different positions on this “bell curve” of responses. Dr. O’Sullivan set up the glucose challenge test we use today to be carried out in the early third trimester, when pregnancy has definitely shifted to a different, much more anabolic state, induced by high human chorionic somatomammotrophin, cortisol, and estrogen.
A first trimester glucose challenge may provide confusing results. In a woman with the risk factors below, seeing what her fasting and two-hour post meal glucose excursions are may be more helpful. If the values quoted above, comparable to those obtained in non-pregnant women, are obtained, PGDM is quite likely.
Glycosylated hemoglobin levels (HbA1C) levels offer limited assistance in non-type 1 pregnant diabetics. Because of the physiologic hemodilution of pregnancy, which will also dilute HbA1C, they almost always look great! However, this “physiologic anemia” does not develop until the mid second trimester, and an elevated early trimester HbA1C value (>6.5%) may be an important clue to the woman’s pre-gestational carbohydrate metabolism. Likewise, since embryogenesis is complete by 9 weeks gestation, interventions aimed at lowering glucose after that time are not likely to have a significant impact on the prevention of hyperglycemia-induced teratogenesis. It would have been great to have found this woman pre-conceptually, established good control, and put her on folate, but now, our interventions may not be timely at all. Conversely, women with a first trimester HbA1C >8.5% have an incidence of fetal anomalies of upwards of 20 per cent. Such women certainly deserve referral for a second trimester comprehensive (“level 2”) targeted ultrasound to carry out a detailed survey of the fetal anatomy.
Our recommendation would be against labeling women as pre-gestational diabetics if they don’t meet the ADA criteria > 126 mg/dL fasting and/or >200 mg/dL post prandial glucose. (See First trimester GDM below)
We have searched extensively and have not been able to find a single evidence-based recommendation as to the validity of first trimester glucose screening to predict, just textbook “expert opinions”. One small study from Europe found that women diagnosed with GDM in the first trimester were more likely to need insulin therapy during pregnancy than those diagnosed at 24-28 weeks, but long term outcomes were not addressed. Please note the usual criteria are only based on giving our clients their 50 g 1-hour glucose challenge (and possible 3-hour diagnostic 100 g glucose tolerance test) at the recommended interval of 24-28 weeks, during “the anabolic phase” of pregnancy.
We should avoid labeling women as pre-existing diabetic, and instead care for them as they have GDM just with a slightly higher level of suspicion. They may have GDM which can be controlled with diet and exercise (class A1), or need medical therapy (insulin or glyburide), i.e., GDM, class A2. Perhaps a significant number of the latter group actually do have PGDM which can be determined post partum.
A new diagnostic category: First Trimester GDM
We suggest patients whose first diagnosis of glucose intolerance is in the first trimester simply be called ‘First Trimester GDM’. Here is an approach to last part of her Progress note:
Assessment:
1. IUP, 8 wks.
2. 1 st Trimester GDM
possible pregestational DM, status to be determined pp
Plan:
monitor for development of GDM-A2
will require increased surveillance if becomes GDM-A2
otherwise manage as GDM-A1
need to re-test for glucose intolerance postpartum
We would manage the First trimester GDM patient according to their and their fetus’ needs now, and establish a definitive diagnosis later. If you have a high level of suspicion initially, you can order a spot urine Protein/ Creatinine ratio, or a 24-hour urine for creatinine clearance and total protein, as well as arrange a baseline dilated retinal exam. If the patient requires medical therapy, she will also need fetal surveillance after 32 weeks. There are also psychological benefits with more accurate diagnoses.
Those patients with abnormal OGTTs diagnosed after completion of the first trimester should simply be diagnosed with ‘gestational diabetes mellitus’.
From a public health standpoint, it will behoove us to assiduously follow up such a woman as presented in the case vignette at six weeks post partum. Significant numbers of Native American women with GDM will become overt type 2 diabetics within five years of the index pregnancy. Post partum we need to be sure she gets her 75 g 2-hour screen, or fasting glucose evaluated by the usual adult criteria, in order to establish the level of abnormal carbohydrate metabolism. If normal, then she should be re-screened with a fasting glucose every 3 years.
When the results of the large international multi-center Hyperglycemia and Pregnancy Outcomes (HAPO) study, which is using the 75 g glucose tolerance test to diagnose GDM, are published, we will have the evidence to enable us to simplify the whole process.
In summary, the term ‘First Trimester GDM’ raises the appropriate level of suspicion among your fellow providers, while providing the patient the most accurate diagnosis for the rest of her lifetime.
Your comments on what works for you at your service units are welcome.
George J. Gilson, MD (ANMC)
John B. Miller, M.D. (Zuni)
Neil Murphy, M.D. (ANMC)
Deputy OB/GYN CCC Editorial comment:
Drs. Gilson, Miller, and Murphy raise a excellent point about the challenges of managing an early diagnosis of gestational diabetes.
Their proposed new diagnostic category, First Trimester GDM, highlights the increased risk status of these women, without making a diagnosis of pre-gestational diabetes until confirmatory testing has been conducted after delivery. We have seen a number of women in similar circumstances in our practice and find that they benefit greatly from intensive education during pregnancy, although assuring completion of postpartum testing remains challenging.
The use of this new diagnostic category would help identify these women for intensified efforts for postpartum follow-up and provide efficient communication of risk to other members of the health care team. It would be worthwhile to consider adding this new diagnostic category in your facility’s Diabetes in Pregnancy guidelines when you next update them… Jean Howe, MD
Risk factors triggering a GDM screen at the first prenatal visit
History
macrosomic infants over 4000g (8 lbs. 14 oz.)
family history of first degree relatives with diabetes
gestational diabetes in a previous pregnancy
overweight (pre-pregnancy weight ≥ 110 % of ideal body weight (pre-pregnancy weight BMI ≥ 27) -prior term intrauterine fetal demise -prior infant with a birth defect or congenital anomaly -habitual abortion ( ≥ 3 consecutive SAB)
Current pregnancy:
age over 35 years -unexplained polyhydraminos -persistent glycosuria
Online Resource
Diagnosis and Classification of Diabetes Mellitus Diabetes Care 30:S42-S47, 2007
Other References
- American Diabetes Association. Gestational diabetes mellitus (Position Statement). Diabetes Care 2002; 25 (S1): S94-96.
- ibid. Diabetes Care 2003; 26 (S1): S103-105.
- ibid. Diabetes Care 2004; 27 (S1): S88-90.
- American Diabetes Association. Standards of medical care in diabetes (Position Statement). Diabetes Care 2005; 28 (S1): S4-36.
- Omori Y, Jovanovic L. Proposal for the reconsideration of the definition of gestational diabetes. Diabetes Care 2005; 28:2592-3.
- Nahum GG, Huffaker BJ. Correlation between first- and early third-trimester glucose screening test results. Obstet Gynecol 1990; 76:709-13.
- Omori Y, et al. Comparison of diagnostic criteria of impaired glucose tolerance, borderline, and gestational diabetes mellitus: Blood glucose curve and immunoreactive insulin responses. Diabetes 1991; 40 (S2): 30-4.
- Bartha JL, et al. Gestational diabetes mellitus diagnosed during early pregnancy. Am J Obstet Gynecol 2000; 182:346-50.
- Brody S, et al. Screening for gestational diabetes: A summary of the evidence for the UPSTF. Obstet Gynecol 2003; 101:380-92.
Contents Summary ‹ Previous | Next › From Your Colleagues
OB/GYN
Dr. Neil Murphy is the Obstetrics and Gynecology Chief Clinical Consultant (OB/GYN C.C.C.). Dr. Murphy is very interested in establishing a dialogue and/or networking with anyone involved in women's health or maternal child health, especially as it applies to Native or indigenous peoples around the world. Please don't hesitate to contact him by e-mail or phone at 907-729-3154.
