Gestational dating ultrasound
The first 2 are subject to considerable error and should only be used when ultrasonography facilities are not available.The date of feeling the first fetal movements (quickening) is far too unreliable to be useful.Gestational age (GA) has traditionally been estimated from the date of the last menstrual period (LMP).This estimation assumes that conception occurs on day 14 of the cycle.
Tape measurement of the symphysis-fundus height may be useful up to 28-30 weeks' gestation, beyond which it becomes too inaccurate for dating.
In rare cases, the date of coitus is known, and this may be useful in calculating the length of pregnancy.
For related information, see Medscape's Pregnancy Resource Center.
Knowing the date of the first positive pregnancy test result allows the calculation of a minimum GA. For example, if the test was performed 4 weeks ago and the test is known to return positive results as early as 1 week after conception, then the minimum conceptional age (CA) would be 5 weeks (GA, 5 2 = 7 wk of amenorrhea).
This information can be useful in clinical practice if the test finding has been documented by a health care professional.