Gestational Age vs Fetal Age
Why you are "four weeks pregnant" at conception plus two weeks.
Two ways of counting
Gestational age counts from the last period, and fetal age counts from conception, about two weeks later.
Why clinicians use gestational age
The last period is easier to know than the day of conception, so all schedules and milestones use gestational age.
Milestones
The first trimester ends at 13 weeks 6 days, the anomaly scan is usually at 18 to 22 weeks and viability is considered from around 24 weeks.
Try it: Gestational Age Calculator
Example with sample values. Open the full calculator →
Gestational age12 weeks 0 days
Trimesterfirst trimester
Days to due date196
Gestational age counts from the first day of the last menstrual period, about two weeks before conception.
Educational content only. This article does not replace advice from a qualified health professional. Medical disclaimer.