From the Research
Pregnancy is typically divided into three trimesters, each lasting approximately 13-14 weeks, with the first trimester spanning from conception (week 0) through week 13, the second trimester covering weeks 14 through 27, and the third trimester extending from week 28 until delivery, which typically occurs around week 40. The division of pregnancy into trimesters is a widely used framework for tracking fetal development, scheduling screenings, and monitoring maternal health changes. Some studies have proposed alternative systems, such as dividing pregnancy into four 10-week quartiles or using a developmentally based approach 1, but the three-trimester model remains the most widely used. The use of trimesters helps healthcare providers and expectant parents understand the progression of pregnancy and anticipate physical changes and developmental milestones. Key milestones in each trimester include:
- First trimester: embryo development, major organs forming 2
- Second trimester: fetal growth, movements becoming noticeable 2
- Third trimester: preparation for birth, final fetal development 3 It's worth noting that some medical contexts may use slightly different cutoffs, but the three-trimester model is generally accepted as the standard framework for pregnancy dating 4, 5.