“Am I pregnant?” The answer to this age-old question once demanded a combination of guesswork, intuition, and time. In 1978, however, the long wait to know for sure became a thing of the past. Trumpeted by advertisements as “a private little revolution,” the first home pregnancy tests started appearing on drug store shelves that year. A quarter of a century later, innovations promise to make even the telltale thin blue line obsolete. This web site looks at the history of the home pregnancy test—one of the most ubiquitous home healthcare products in America—and examines its place in our culture.
The home pregnancy test works by identifying the presence of the “pregnancy hormone,” human chorionic gonadotropin (hCG), in urine. Understanding hCG:
(See below for definitions of specific terms)When NIH scientists did their research in the early 1970s on measuring and identifying hCG, they were not sure what the role of hCG was in normal pregnancy, what normal levels of hCG should be, or how they would rise and fall during the course of the pregnancy.

Much research has been done, however, in the last 30 years, to answer these questions. Here is what happens during the menstrual cycle and pregnancy as it relates to hCG.

There are three phases of the menstrual cycle:

1. Follicular phase: the pituitary gland increases release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates growth of follicles in the ovary and prompts the release of estrogen from the ovary. Estrogen, in turn, causes the thickening of the endometrium. One follicle will mature and release an ovum (egg). LH is secreted mid-cycle, and stimulates the release of that ovum from the follicle in the ovary.

2. Ovulatory phase: The ovum is released from the follicle and makes its way down the fallopian tubes toward the uterus, perhaps to be fertilized along the way. There are increased levels of LH during this phase. An ovulation prediction kit will detect a surge in LH about 1-2 days before ovulation.

3. Luteal phase: this covers the time from ovulation through the next menstrual period. Following ovulation the follicle that released the ovum closes and becomes the corpus luteum. LH sustains the corpus luteum until, in the event of pregnancy, it is supported by hCG. Increased production of estrogen and progesterone follow. Both hormones prepare the endometrium for the implantation of a fertilized egg.

If pregnancy does not occur: the corpus luteum regresses, the hormone levels of progesterone and estrogen go back down, and the breakdown of the endometrium causes menstrual bleeding. The corpus luteum will last 10 to14 days and then die. If pregnancy does occur, the corpus luteum begins to produce hCG. This hormone stimulates the corpus luteum, preventing it from dying in early pregnancy. The corpus luteum produces estrogen and progesterone in the early part of the pregnancy, and is therefore vital for maintaining that pregnancy. Later, these hormones will be produced by the placenta. Therefore, if the corpus luteum does not function early on, the uterine lining will not support a pregnancy. Menstruation will occur and the pregnancy will miscarry. hCG is produced by the placenta in pregnancy, specifically by what is called the trophoblast of the chorionic villi. Levels are higher in the first trimester and then decrease as other hormones take over the job of protecting the embryo and, later, the fetus.If, for any reason, the embryo does not develop normally, the trophoblast will lose its capacity to sustain the rapid rise in hCG necessary to maintain the corpus luteum. To force support of the corpus luteum and sustain a pregnancy, hCG can be used clinically as part of IVF (in-vitro fertilization) and other infertility programs.