• 1.  Weeks for each Trimester

    Posted 02-17-2022 13:42
    I have used my wheel to determine weeks of gestation for each Trimester.  My MFM education Team is making a Coding Guide for MFM. There are several different answers to this on Google.  What should we be usung?
    ACOG states that:
    • the first trimester is from week 1 to the end of week 12
    • the second trimester is from week 13 to the end of week 26
    • the third trimester is from week 27 to the end of the pregnancy
    Another site says:

    First trimester

    First day of last menstrual period (day 0) up to and including 13 weeks 6 days

    Less than 14 weeks 0 days

    Second trimester

    14 weeks 0 days up to and including 27 weeks 6 days

    14 weeks 0 days to less than 28 weeks 0 days 

    Third trimester

    28 weeks or more

    28 weeks 0 days to delivery

    Mary Knigge

  • 2.  RE: Weeks for each Trimester

    Posted 02-17-2022 14:01

    CPT defines trimesters as -

    Trimesters are counted from the first day of the last menstrual period. They are defined as follows:

    1st trimester- less than 14 weeks 0 days

                    2nd trimester- 14 weeks 0 days to less than 28 weeks 0 days

                    3rd trimester- 28 weeks 0 days until delivery




    Erin Kornovich, CPC | Coding Specialist II – Maternal Fetal Medicine & Physiatry


    P: 320-251-2700, ext. 52373


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  • 3.  RE: Weeks for each Trimester

    Posted 02-18-2022 10:41
    Hi Mary,
    Please see 
    First trimester (first day of LMP to 13 weeks and 6 days)
    Second trimester (14 weeks and 0 days to 27 weeks and 6 days)
    Third trimester (28 weeks and 0 days to 40 weeks and 6 days)

    Coding follows these definitions.


    Fadi BSAT, MD, FAIUM
    Chair, SMFM Practice Management Division