If a menstrual period is a week or more late in a woman who usually has regular menstrual periods, she may be pregnant.
After pregnancy is confirmed, the woman’s doctor asks her when her last menstrual period was.
The doctor calculates the approximate date of delivery by counting back 3 calendar months from the first day of the last menstrual period and adding 1 year and 7 days.
If results are positive, the woman should contact her doctor, who may do another pregnancy test to confirm the results.
Doctors test a sample of urine or sometimes blood from the woman to determine whether she is pregnant. One of these tests, called an enzyme-linked immunosorbent assay (ELISA), can quickly and easily detect even a low level of human chorionic gonadotropin in urine.
For example, if the last menstrual period was January 1, the doctor counts back 3 months to October 1, then adds 1 year and 7 days.
Human chorionic gonadotropin is a hormone produced by the placenta early in pregnancy.Results of home pregnancy tests are accurate about 97% of the time.If results are negative but the woman still suspects she is pregnant, she should repeat the home pregnancy test a few days later.The first test may have been done too early (before the next menstrual period is expected to start).Some tests can detect the very low level that is present several days after fertilization (before a menstrual period is missed). During the first 60 days of a normal pregnancy with one fetus, the level of human chorionic gonadotropin in the blood approximately doubles about every 2 days.These levels can be measured during the pregnancy to determine whether the pregnancy is progressing normally.