1st Trimester

Why are there variations as to when the 2nd tri starts?

Some sites say I'll be in my 2nd tri end of Feb, and others say in March - does anyone know how there can be conflicting dates when they all have the due date correct? I'm trying to figure out when it is because then I can finally tell the world, lol! Can anyone solve this mystery? ;) 
THANKS

Re: Why are there variations as to when the 2nd tri starts?

  • I'm still confused about these things so I am no help, sorry. I think I switched over at 13w6days or something like that.
  • my midwives were explaining this to me yesterday... the three trimesters are not equally divided which is why its hard to calculate.  Some do 13wks3d as that seems to be the closest to 1/3 of 40 weeks... but since many pregnancies are 41 or 42 weeks, then that calc. is off. I'm switching over soon.. and now that we have confirmed hb and a live baby and have reached 3 months, moving forward is easier.
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  • I think someone explained once that some base it on dividing the pregnancy into 3 equal parts while others use developmental milestones to mark the beginning/end of trimesters.

    No matter how you divide it out though, 12 weeks is when the risk of m/c drops the most significantly.

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  • Also, even though we base EDD on 40 weeks, there are also different definitions of "full term." I believe anything after 38 weeks is generally considered full term.
  • Here are the different explinations:

     

    The three basic ways to calculate trimesters

     
    There are basically three ways of dividing up a pregnancy into the three trimesters; they are by:
    Development,   Gestation,   Conception. They give different dates for when the second trimester begins and for when the third trimester begins. Your health care provider might prefer to use the Development method, while another Midwife or Doctor may use the Gestation method.
    I am sure they do that just to confuse pregnant women.  Big Grin
    Development:
    This uses actual developmental stages to divide up a pregnancy. From LMP to 12 weeks the embryo develops all the major organs and becomes a fetus. From 12 weeks to 27 weeks the fetus continues developing and reaches viability. From 27 weeks on the fetus finishes development and prepares for delivery. Here the second trimester begins at 12w 0d and the third at 27w 0d.
    Gestation:
    With this method you take the 40 weeks of gestation and divide by three. Here the second trimester begins at 13w 3d and the third at 26w 6d.
    Conception:
    This method is where you take the 38 weeks of post conception development, divide by three, and add two weeks. Here the second trimester begins at 14w 5d and the third at 27w 3d.


    No matter what method is used; a pregnancy has a beginning, middle and end. You can use the trimester dates from your Doctor, a book or a website, whichever you feel most comfortable with.

     https://www.baby2see.com/trimester_calculator.html

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