12/24/04njm

Q. What are the best cut-offs to use while monitoring diabetes in
pregnancy therapy?

A. Ideally: FBS \< 95 mg/dL, 1 hr. \< 130 mg/dL and 2 hr \< 120 mg/dL.
See the details below

Many providers use fasting blood glucose (FBS) of \< 105 mg/dL, plus
representative post prandial glucose levels. Other experts recommend
lower FBS levels, e.g., 90-95 mg/dL (Laird)

Perhaps the most commonly used post prandial cut-off is 2 hour post
prandial \< 120 mg/dL, but there is actually better quality data for
130-140 mg/dL at one hour post prandial.

In any case there is enough latitude in the literature that glucose
values can be monitored at the convenience of the patient. Please review
the Monitoring information below\*.

Have you ever been confused about the differences in glucose results
between venous, whole blood, plasma, and serum or between venous and
capillary (fingerstick) samples?

See Venous versus capillary and plasma versus whole blood samples
below.\*\*

Here other good resources:

**ANMC revised Diabetes in Pregnancy guidelines**

<http://www.ihs.gov/MedicalPrograms/MCH/w/documents/DMPreg102504_000.doc>

**Treatment and course of gestational diabetes mellitus**

<http://www.uptodateonline.com/application/topic.asp?file=pregcomp/27083&type=A&selectedTitle=2~13>

These two resources also offer free CME

**Diabetes in pregnancy: Screening and diagnosis**

[[http://www.ihs.gov/MedicalPrograms/MCH/M/DP01.asp#top]{.underline}](http://www.ihs.gov/MedicalPrograms/MCH/M/DP01.asp#top)

**Diabetes in pregnancy: Management and postpartum**

[[http://www.ihs.gov/MedicalPrograms/MCH/M/DP21.asp#top]{.underline}](http://www.ihs.gov/MedicalPrograms/MCH/M/DP21.asp#top)

**\*Monitoring glucose levels**

The optimal frequency of blood glucose testing in patients with GDM has
not been established. Whether daily testing is essential for women with
GDM has not been proven. One large, prospective trial compared
seven-times-daily self-glucose monitoring using memory-based reflectance
meters with weekly fasting and 2-hour laboratory glucose determinations
supplemented by four-times-daily self-monitoring with only test strips
and no meters (Langer 1994). The more intensively monitored group had
fewer primary cesarean deliveries and fewer macrosomic neonates, and
their infants were less likely to experience shoulder dystocia and
neonatal hypoglycemia than the more conventionally monitored group.
Other centers have reported similar results with four-times-daily
glucose monitoring (de Veciana, Goldberg). Although daily self-glucose
monitoring has not been demonstrated to reduce perinatal mortality in
women with GDM, it appears to be useful in reducing potentially adverse
outcomes such as macrosomia.

However, evidence from well-designed, randomized trials that compare
daily self-glucose monitoring with less frequent assessment in women
with GDM is still needed.

Further uncertainty surrounds the timing of glucose determinations and
the selection of appropriate thresholds for intervention. In nonpregnant
individuals, diabetes is most often managed using preprandial glucose
determinations. However, the fetus may be more sensitive to glucose
excesses than to the nadirs of glucose values at various times of the
day. In studies of preexisting diabetes, 1-hour postprandial glucose
values were found to be more predictive of fetal macrosomia than were
fasting values (Jovanovic-Peterson), and a 1-hour value of 130 mg/dL or
more was found to be an appropriate threshold (Combs). A randomized
trial compared preprandial with 1-hour postprandial glucose measurements
in 66 women whose GDM was severe enough to require insulin treatment by
30 weeks of gestation (monitoring (de Veciana). Macrosomia, neonatal
hypoglycemia, and cesarean deliveries for shoulder dystocia were
significantly lower among those who had postprandial monitoring, and
their glycohemoglobin levels also decreased more markedly than did the
levels of the subjects who used preprandial monitoring. No studies are
available to compare the efficacy of 1-hour postprandial versus the more
traditional 2-hour postprandial glucose determinations.

Because these studies only included individuals with preexisting
diabetes or those with GDM severe enough to require insulin treatment by
30 weeks of gestation, it remains to be established whether fasting or
preprandial glucose measurements will suffice for individuals with
milder forms of GDM. One study demonstrated a moderate correlation
between fasting and 2-hour postprandial glucose values in GDM; if the
fasting value was below 105 mg/dL, then only 17% of the 2-hour values
exceeded 120 mg/dL (Huddleston). Given the available data, postprandial
glucose values appear to be most effective at determining the likelihood
of macrosomia and other adverse pregnancy outcomes in patients with GDM.

ACOG Practice Bulletin No. 30. Gestational Diabetes. American College of
Obstetricians and Gynecologists. Obstet Gynecol 2001;98:525--538 (Level
III)

ACOG Members

<http://www.acog.com/publications/educational_bulletins/pb030.cfm>

Non-ACOG Members

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11547793&dopt=Abstract>

**\*\*Venous versus capillary and plasma versus whole blood samples**

<http://www.ihs.gov/MedicalPrograms/MCH/M/DP09.asp#top>

Have you ever been confused about the differences in glucose results
between venous, whole blood, plasma, and serum or between venous and
capillary (fingerstick) samples?

Whole blood versus plasma or serum

The glucose concentration measure in plasma or serum of a given specimen
is approximately 14-15% higher than the concentration in the same sample
before separation of the cells (whole blood).\
\
This may be more than you want to know, but\...\....the reason for this
discrepancy is that 35-45% of the volume of whole blood (depending on
the hematocrit) is composed of red blood cells. Approximately 35% of the
red blood cell is hemoglobin, and glucose is not distributed in this
part of the cell. Therefore, for example, glucose is excluded from about
15% of a blood sample with a hematocrit of 43% (0.35 x 43 =
approximately 15%). In other words, only 85% of the volume of used for
the assay contains glucose, but the results are expressed for the entire
volume. Thus, values obtained with whole blood are approximately 15%
lower than with plasma or serum, in which glucose is distributed
throughout the entire volume.\
\
One further wrinkle is that the original GDM studies by Dr. O\'Sullivan
utilized Somogyi-Nelson whole blood technique. An enzymatic process
analyzes most glucose samples now. These enzymatically derived values
have been shown to be about 5mg/dL lower than the Somogyi-Nelson because
the enzymatically derived values exclude reducing sugars.\
\
**Sample site (fingerstick or venous)**

Arterial glucose levels are higher than venous concentrations because
the peripheral tissues have not yet had the opportunity to extract the
glucose. Capillary blood contains a mixture of arterial and venous blood
and is often obtained for sampling from the pads of the fingers. If
these areas are warmed or stimulated in order to increase blood flow,
the arterial contribution to the sample is enhanced. (Davidson)\
\
In the fasting state, peripheral tissues (with the exception of red
blood cells in the brain) do not use glucose to a large extent; hence
there is little difference between capillary and venous samples.\
\
After a glucose challenge, depending on the amount of glucose
administered and the timing of the sample, there are appreciable
differences between capillary and venous samples. As would be expected,
the more glucose given and the earlier the interval at which the sample
is obtained, the greater the difference. For example, 1 hour after the
ingestion of 100g of glucose, capillary values are 30-40mg/100ml higher
than venous levels.\
\
On average, arterial glucose is 7% greater than venous glucose.

Reflectance photometers

As technology has advanced the manufacturers have taken all the above
into consideration. For example, Accu-Chek(tm) is calibrated to deliver
plasma like results.\
\
[Murphy et al
1994](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8190419&dopt=Abstract)
found a reflectance photometer to be both accurate and precise in a
single operator situation. On the other hand, one most consider both the
accuracy and the precision of reflectance photometers among individuals
with a wide-variety of skill levels.\
\
At this time reflectance photometers are helpful in monitoring the
clinical care of a GDM patient, but they not felt to display enough
accuracy and precision in a wide variety of settings to be recommended
for diagnosis or screening for GDM.\
\
**Bottomline**

If you are using a reflectance photometer with fingerstick samples to
monitor your GDM patient, then check with the manufacturer\'s
specifications to see to what kind of sample the device is calibrated,
e.g., Accu-Chek is calibrated to deliver plasma like results.

**References:**

Combs CA, Gunderson E, Kitzmiller JL, Gavin LA, Main EK. Relationship of
fetal macrosomia to maternal postprandial glucose control during
pregnancy. Diabetes Care 1992;15:1251--1257 (Level II-2)

de Veciana M, Major CA, Morgan MA, Asrat T, Toohey JS, Lien JM, et al.
Postprandial versus preprandial blood glucose monitoring in women with
gestational diabetes mellitus requiring insulin therapy. N Engl J Med
1995;333:1237--1241 (Level I)

Goldberg JD, Franklin B, Lasser D, Jornsay DL, Hausknecht RU,
Ginsberg-Fellner F, et al. Gestational diabetes: impact of home glucose
monitoring on neonatal birth weight. Am J Obstet Gynecol
1986;154:546--550 (Level II-2)

Huddleston JF, Cramer MK, Vroon DH. A rationale for omitting two-hour
postprandial glucose determinations in gestational diabetes. Am J Obstet
Gynecol 1993;169:257--264 (Level II-2)

Jovanovic-Peterson L, Peterson CM, Reed GF, Metzger BE, Mills JL, Knopp
RH, et al. Maternal postprandial glucose levels and infant birth weight:
the Diabetes in Early Pregnancy Study. The National Institute of Child
Health and Human Development-Diabetes in Early Pregnancy Study. Am J
Obstet Gynecol 1991;164: 103--111 (Level II-2)

Laird, J, McFarland, KF. Fasting blood glucose levels and initiation of
insulin therapy in gestational diabetes. Endocr Pract 1996; 2:330.

Langer O, Rodriguez DA, Xenakis EM, McFarland MB, Berkus MD, Arrendondo
F. Intensified versus conventional management of gestational diabetes.
Am J Obstet Gynecol 1994;170:1036--1047 (Level II-1)

[Murphy NJ, Meyer BA, O\'Kell RT, Hogard
ME](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7884757&dopt=Abstract)
Carbohydrate sources for gestational diabetes mellitus screening. A
comparison. J Reprod Med 1994 Dec;39(12):977-81 (Level I)

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7884757&dopt=Abstract>

[Murphy NJ, Meyer BA, O\'Kell RT, Hogard
ME](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8190419&dopt=Abstract)[.]{.underline}
Screening for gestational diabetes mellitus with a reflectance
photometer: accuracy and precision of the single-operator model. Obstet
Gynecol 1994 Jun;83(6):1038-42 (Level II-2)

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8190419&dopt=Abstract>