support
amboss lists trimesters as week 1-13, weeks 14-26, weeks 27-40
Support also. Dynamed lists as 1st = 0-12, 2nd as 13-24, 3rd as 25+, indicating some variability in definitions between sources. However, per ACOG, 1st = 0-13+6, 2nd = 14-27+6, 3rd = 28+. https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy - thus though I feel the specific numbers are less important than a rough idea, ACOG seems like the best source. Wasn’t able to easily spot numbers in FA.