Gestational age (also called menstrual age or menstrual dating) is
estimated in completed days or weeks from the date of the woman's
last menstrual period (LMP). Ovulation is assumed to occur two weeks
after the LMP. Accurate menstrual dating depends upon knowledge of
LMP and regular 28-day cycle length and is considered to have an accuracy
of ±2 weeks. Embryonic or fetal age is calculated from the
presumed date of ovulation and is therefore two weeks less than gestational
age measured from the LMP.
The first trimester of pregnancy corresponds to a gestational age
of < 14 weeks. Early pregnancy is typically defined as <10
weeks' gestation. The following table offers synonymous terms used
to describe gestational ages in the first trimester of pregnancy.
| |
Gestational Age
|
Gestational Age
|
Embryonic Age
|
|
Very early pregnancy
|
< 42 days
|
< 6 weeks
|
< 4 weeks
|
|
Very early pregnancy
|
< 49 days
|
< 7 weeks
|
< 5 weeks
|
|
Early pregnancy
|
< 56 days
|
< 8 weeks
|
< 6 weeks
|
|
Early pregnancy
|
< 63 days
|
< 9 weeks
|
< 7 weeks
|
