What is usu considered the end of Trimester 1?

ksteeb611 · April 2012

I thought 13 wks 3 days, but I've read 12 wks elsewhere. Thanks:)

danieliza1127 · April 2012

I always thought it was 12 weeks but then when I was actually in my first trimester, I read that week 14 is the beginning of the second trimester. I've seen week 13 and week 14.

mswood1977 · April 2012

There are 3 ways to calculate the different trimesters. Depending on which you use the end of the 1st trimester/start of the 2nd trimester can be 12 weeks, 13w3d or 14w5d.

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.

by 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.

by Gestation:

With this method you take the 40 weeks of gestation and divide into three equal stages. Here the second trimester begins at 13w 3d and the third at 26w 6d.

by Conception:

This method is where you take the 38 weeks of post conception development, divide by three, into the three equal trimesters. Here the second trimester begins at 14w 5d and the third at 27w 3d.

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