Comprensión de la Edad Gestacional
How Gestational Age Is Calculated
Gestational age is measured from the first day of your last menstrual period (LMP), not from the date of conception. This is the standard medical convention because the exact date of conception is usually unknown. A full-term pregnancy is 40 weeks (280 days) from the LMP. Since ovulation typically occurs about 14 days after the start of your period, the actual fetal age is about 2 weeks less than the gestational age.
Naegele's Rule for Due Date
The standard due date calculation uses Naegele's Rule: add 7 days to the first day of the LMP, subtract 3 months, and add 1 year. For a 28-day cycle, this gives an estimated due date of 40 weeks from the LMP. If your cycle is longer or shorter than 28 days, adjustments can be made: add or subtract the difference from 28 to the calculated due date.
First Trimester (Weeks 1-13)
The first trimester is a period of rapid development. By week 8, all major organs have begun to form. The neural tube closes by week 6, which is why folic acid supplementation before and during early pregnancy is critical. Common symptoms include nausea, breast tenderness, fatigue, and frequent urination. The risk of miscarriage is highest during this trimester.
Second Trimester (Weeks 14-27)
The second trimester is often called the golden period because many women experience increased energy and reduced nausea. The fetus grows significantly, and you may begin to feel movement (quickening) around weeks 18-22. Key prenatal tests including anatomy scans and glucose screening are performed during this period.
Third Trimester (Weeks 28-40)
The third trimester involves rapid fetal weight gain and maturation of the lungs and brain. The fetus typically moves into a head-down position in preparation for birth. Prenatal visits become more frequent (every 2 weeks, then weekly). Full term is considered 39-40 weeks, while 37-38 weeks is early term.