Pink Mom MathTrimester Calculator
Enter your last menstrual period (LMP) to see the exact date ranges for all three pregnancy trimesters.
Understanding Pregnancy Trimesters
Pregnancy is divided into three trimesters, each representing roughly one-third of the 40-week gestational period. The boundaries are defined in terms of gestational age (counted from LMP).
The first trimester (weeks 1-12) is when all major organ systems develop. This is the period of highest miscarriage risk, and most routine prenatal screening occurs here (nuchal translucency scan, first-trimester blood work).
The second trimester (weeks 13-27) is characterized by rapid fetal growth. The anatomy scan at weeks 18-20 checks for structural abnormalities. Most women feel the baby move for the first time (quickening) during weeks 16-22.
The third trimester (weeks 28-40) involves continued growth and preparation for birth. The baby turns head-down (vertex position) and the lungs mature in preparation for breathing outside the womb.
Frequently Asked Questions
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This calculator provides estimates for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health or your baby's health.
Based on ACOG trimester boundary definitions.