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PregnancyHow pregnancy week is calculated
Medical gestational age is counted from the first day of the last menstrual period (LMP), not from the conception date. This is standard obstetric practice, since the exact conception date is hard to determine, while the last period date is usually known.
The three trimesters of pregnancy
- First trimester (weeks 1-13): formation of major organs and systems, highest risk of miscarriage.
- Second trimester (weeks 14-27): often called the "golden period" — morning sickness fades, energy returns, fetal movement becomes noticeable.
- Third trimester (weeks 28-40+): active fetal weight gain, body preparation for labor.
Why fruit-size comparisons are popular
Many parents find it helpful to visualize fetal size through comparisons with familiar objects — fruits or vegetables. This isn't a medical term but a popular way to make abstract centimeters more tangible and understandable.
Fetal sizes are population averages and can vary in individual cases. An accurate assessment of fetal development is provided by a doctor during a scheduled ultrasound.
FAQ
Why is pregnancy counted from the last period instead of conception?
The exact conception date is hard to determine, while the last menstrual period date is usually known. Medical gestational age is traditionally counted from LMP.
How many weeks does a normal pregnancy last?
A full-term pregnancy lasts 37-42 weeks, averaging 40 weeks from the first day of the last menstrual period.
Is fetal size the same for all women at the same week?
No, sizes are population averages. Actual fetal size can vary and is individually assessed by a doctor during ultrasound.