11/28/04 njm

**Q.** What is the best screening cut-off for gestational diabetes
mellitus?

**A**. A cut-off of 140 mg/dL has 10% less sensitivity than a threshold
of 130 mg/dL but fewer false-positive results; either threshold is
acceptable. See this discussion

The most commonly used cut-off in Indian Country is 140 mg/dL. The
screening test threshold at which a diagnostic GTT is recommended will
be arbitrary. The higher the threshold, the lower the sensitivity but
the better the specificity and the lower the likelihood of a
false-positive test result.

The lower the threshold, the higher the sensitivity but the higher the
likelihood of a false-positive test result and thus the performance of
an unnecessary diagnostic GTT. O\'Sullivan and Mahan (1) used venous
whole blood samples and the Somogyi-Nelson method of glucose analysis.
At the recommended threshold of 130 mg/dL, the screening test had a
sensitivity of 79% and a specificity of 87%. When venous plasma and
specific enzymatic methods of glucose analysis were used, 10% of women
with GDM manifested screening test values between 130--139 mg/dL (2).

Absolute sensitivity levels could not be determined because women with
screening test values below 130 mg/dL did not undergo oral GTTs. When
the threshold was lowered from 140 mg/dL to 130 mg/dL, the number of
women requiring glucose tolerance testing increased from 14% to 23%, or
approximately one quarter of patients.

Although a threshold of 140 mg/dL was recommended in the past, the most
recent position statement of the American Diabetes Association ascribes
a sensitivity of approximately 80% to this cutoff and 90% sensitivity
with a threshold of 130 mg/dL and leaves the choice open (3). Because
the precise cost-benefit ratio of diagnosing GDM remains unresolved,
either threshold is acceptable.

Here is some more discussion from the original question:

(please excuse the informal manner below in advance)

**Q.** The docs are suddenly having questions about what to use

for the one hour glucola cut off for pregnancy\....\>140 \>135 \>130.

I see the ANMC guidelines from 2002 state \>140.

UpToDate states if you use \>130, you will catch 90% or have 90%
sensitivity for GDM.

We have had a bunch of recent 135, 136, 139 values in women measuring
big, or then they have one abnormal value on their 3 hour and we are
watching them trying to figure out if they are really GDM or not

**A.** As you know the screening cut off\*\* is irrelevant to their
actual diagnosis. All that matters is what happens on their 3 hr OGTT.

Since the Tallargio paper (4), quite a long time ago now, we have
counseled all the one abnormal value on OGTT pts with the same diet
counseling as an official GDM because they are known to have higher
rates of macrosomia.

In our new GDM guidelines, which will be released next month, patients
who have one abnormal OGTT result prior to 32 weeks will get a repeat 3
hr OGTT sometime after 32 weeks. In the literature, you can get at least
1/3 of those to become officially abnormal when you repeat the OGTT.

\*\*any of those cut-offs are fine.

Yes, as you decrease the cut-off towards 130 it just means that you
increase the sensitivity, but that also means that a larger percent of
women will have to now get 3 hr OGTT which turn out to be normal a lot
more often too\....

\...read as\....you do more OGTTs and many more that end up being normal

As the OGTT is bit of hassle from the pt\'s standpoint, we have chosen
the higher traditional cut-off.

We can live with the traditional sensitivity and specificity because we
will f/u with a repeat OGTT if they have one abnormal as I mentioned
above. That approach results in less overall normal OGTTs in otherwise
normal patients. If your group has a strong feeling to lower cut-off,
that is OK\....and either of the lower cut-offs work OK, with the
proviso that you get a lot more normal OGTTs back.....

By the way here are our two free CME modules that address GDM. They have
the current, e.g., not the brand new 2004 GDM guidelines incorporated,
but they are still worth the read\....and could be free CMEs if anyone
was interested

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)

Other resources

Diabetes in Pregnancy Guidelines

[[http://www.ihs.gov/MedicalPrograms/MCH/M/documents/DMPreg102504_000.doc]{.underline}](http://www.ihs.gov/MedicalPrograms/MCH/M/documents/DMPreg102504_000.doc)

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

ACOG non-members

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

ACOG members

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

1\. Sullivan JB, Mahan CM, Charles D, Dandrow R. Screening criteria for
high-risk

gestational diabetic patients. Am J Obstet Gynecol 1973;116:895--900
(Level II-2

2.  Coustan DR, Nelson C, Carpenter MW, Carr SR, Rotondo L, Widness JA.
    Maternal age and screening for gestational diabetes: a
    population-based study. Obstet Gynecol 1989;73:557--561 (Level II-2)

3.  Nutritional management during pregnancy in preexisting diabetes. In:
    American Diabetes Association. Medical management of pregnancy
    complicated by diabetes. 3rd ed Alexandria, Virginia: ADA,
    2000:70--86 (Level III)

4.  Tallarigo L, Giampietro O, Penno G, Miccoli R, Gregori G, Navalesi R
    Relation of glucose tolerance to complications of pregnancy in
    nondiabetic women. N Engl J Med 1986 Oct 16;315(16):989-92 (Level
    II-3)

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3762619&dopt=Abstract>