Skip Navigation
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Your Environment. Your Health.

Early Pregnancy Study (EPS)

Epidemiology Branch

Early Pregnancy Study (EPS)

The original purpose of the Early Pregnancy Study—carried out in 1982-86— was to determine the extent of pregnancy loss that occurs before women know they are pregnant. To accomplish this, 221 healthy women who were planning to become pregnant were enrolled at the time they discontinued all methods of birth control. Study participants collected daily urine specimens and kept daily diaries of their intercourse and menstrual bleeding. Urine samples were assayed using a highly sensitive assay for human chorionic gonadotropin (hCG), the key hormone marker of pregnancy. About 25% of pregnancies detectable by hCG did not survive to become clinically recognized, being lost in bleeding that was mistaken as menstrual bleeding.

Further hormonal assays for estrogen and progesterone metabolites in urine made it possible to estimate the day of ovulation in each cycle. Once this key benchmark of the cycle was determined, a number of basic observations about normal pregnancy and its variations have been possible. These include the first accurate descriptions of the fertile days of the menstrual cycle (i.e., the five days before ovulation and the day of ovulation), the time of implantation (six to twelve days after conception) and the incidence of vaginal bleeding in the early days of healthy pregnancies. These data continue to be a rich source of descriptive data on the events of early pregnancy.

Principal Investigators

Allen J. Wilcox, M.D., Ph.D. (Retired)
Scientist Emeritus
Tel 984-287-3686
Donna Baird, Ph.D.
Senior Investigator
Tel 984-287-3690
Fax 301-480-3290
Anne Marie Z. Jukic, Ph.D.
Tel 984-287-3699
Clarice R. Weinberg, Ph.D.
Principal Investigator
Tel 984-287-3697
to Top