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Recording available 2/16-5/2
Recording available 2/16-5/2
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Poster Session 4

Category: Diabetes

Poster Session 4

(1109) First Trimester Hemoglobin A1c Underestimates CGM-Derived Average Glucose

Thursday, February 12, 2026
3:30 PM - 5:00 PM  

    Submitting Author and Presenting Author(s)

  • India Eaford, MD, MS

    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

    • Coauthor(s)

  • DS

    Diana C. Soria-Contreras, PhD

    Research Scientist
    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • KL

    Kyeisha Laurence, BS

    Harvard Medical School
    Harvard Medical School/Boston, Massachusetts, United States

  • DP

    Deepti Pant, MPH

    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • Lydia L. Shook, MD (she/her/hers)

    Assistant Professor
    Department of Obstetrics and Gynecology, MassGeneral Brigham; Division of Maternal-Fetal Medicine; Harvard Medical School
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • TT

    Tanayott Thaweethai, PhD

    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • RP

    Rachel Petherbridge, BSc, MSc

    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • VT

    Veronica Tozzo, PhD

    Postdoctoral Researcher
    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • JH

    John R. Higgins, MD

    Obstetrician & Gynecologist
    Massachusetts General Hospital
    Massachusetts General Hospital/Boston, Massachusetts, United States

  • Camille E. Powe, MD (she/her/hers)

    Associate Professor
    Massachusetts General Hospital
    Boston, Massachusetts, United States

Objective:
Do 1st trimester hemoglobin A1c (A1c) values reflect recent and preconception glucose levels measured by continuous glucose monitoring (CGM)?

Study Design:
We conducted a retrospective study using laboratory and CGM data from pregnant individuals with pregestational diabetes (86.3% Type 1, Table 1). We included gravidas with an A1c measured at up to 14 weeks’ gestation and >33% CGM coverage in the 90 days before A1c. The primary outcome was the difference between average glucose from CGM (AG-CGM) and the average glucose estimated from A1c (AG-A1c) using the commonly used A1C-Derived Average Glucose (ADAG) equation. Our primary analysis used a paired t-test to compare the differences in AG-CGM and AG-A1c in the 1st trimester vs. outside of pregnancy in those with available CGM and A1c data both in the 1st trimester and while not pregnant ( >3 months prior to conception or >6 months postpartum). Secondary analysis compared AG-CGM from data 90 days prior to conception to AG-A1c in the 1st trimester. In exploratory analyses, we used linear regression to examine associations between hemoglobin, pre-pregnancy BMI, or gestational age at 1st trimester A1c and the primary outcome.

Results:
AG-CGM prior to A1c was 14.8 mg/dL higher on average than AG-A1c in the 1st  trimester (n=26) vs. 7.3 mg/dL higher in the same individuals outside of pregnancy (mean pregnancy effect =7.5 [95% CI 0.10-14.8] mg/dL, p=0.047, Figure 1). AG-CGM was 22.2 mg/dL higher on average prior to conception (n=24) than AG-A1c in the 1st trimester vs. 6.9 mg/dL higher in the same individuals outside of pregnancy (mean effect =15.3 [95% CI 6.5-24.2] mg/dL, p=0.002). In exploratory analyses, there was no association between hemoglobin or pre-pregnancy BMI and the difference between AG-CGM and AG-A1c. Later gestational age was associated with a lower difference between AG-CGM and AG-A1c (n=51, β=-3.35 [95% CI -5.50, -1.20] mg/dl per week).

Conclusion:

1st trimester A1c underestimates mean CGM glucose to a greater extent than outside of pregnancy; there is greater underestimation of preconception CGM glucose than recent CGM glucose.