Amenorrhea is considered a type of abnormal menstrual bleeding characterized by the unexpected absence of menstrual bleeding, lasting three months or longer. Menstrual bleeding typically happens approximately once a month when blood and endometrial tissue, or tissue lining the inside of the uterus, sheds from the uterus through the vagina. Menstruation is expected to stop with pregnancy, breastfeeding, and menopause, or the natural cessation of the menstrual cycle at an older age. However, women may also experience amenorrhea because of an underlying health condition, including low body weight or polycystic ovarian syndrome, that may complicate fertility and contribute to decreased quality of life. According to the American College of Obstetricians and Gynecologists, one in twenty-five women experience amenorrhea as a menstrual disorder within their lives at times.

In 1953, Raymond Greene and Katharina Dalton, who were doctors in the UK, published The Premenstrual Syndrome in the British Medical Journal. In their article, Dalton and Greene established the term premenstrual syndrome (PMS). The authors defined PMS as a cluster of symptoms that include bloating, breast pain, migraine-headache, fatigue, anxiety, depression, and irritability. The article states that the symptoms begin one to two weeks before menstruation during the luteal phase of the menstrual cycle, and they disappear upon the onset of the menstrual period. Menstruation is the monthly series of changes a woman's body undergoes in preparation for the possibility of pregnancy. Dalton and Greene described how progesterone affected women during different phases of their menstrual cycles. The paper convinced many about the phenomenon of PMS, and docotors and scientists adopted Dalton's and Green's term. The paper furthered research about the role of hormones in physiology and of conditions linked to the reproductive system.

In 1948, Olive Watkins Smith published 'Diethylstilbestrol in the Prevention and Treatment of Complications of Pregnancy' in the American Journal of Obstetrics and Gynecology. In 632 women treated with diethylstilbestrol, Smith demonstrated that the drug stimulated the production of progesterone, a hormone that regulates the uterine condition during pregnancy. On the basis of her article, and several follow up articles authored by Smith and her husband, George Van Siclen Smith, physicians around the world began prescribing DES to women at risk for pregnancy complications like miscarriage and premature delivery. However, in 1953, researchers at found that DES did not prevent pregnancy complications. In 1970, researchers linked fetal exposure to DES to rare and severe cancers later in life. Researchers labeled DES as an endocrine disruptor, a substance that disrupts the hormone system of the body across multiple generations.

Charles Raymond Greene studied hormones and the effects of environmental conditions such as high-altitude on physiology in the twentieth century in the United Kingdom. Green researched frostbite and altitude sickness during his mountaineering expeditions, helping to explain how extreme environmental conditions effect respiration. Greene’s research on hormones led to a collaboration with physician Katarina Dalton that culminated in the development of the theory that progesterone caused premenstrual syndrome, a theory that became the basis for later research on the condition. In his later career Greene formed the Thyroid Club of London that brought together specialists in the emerging field on endocrinology. Greene’s research on progesterone and thyroid helped researchers study how of the endocrine system functions in women’s reproductive health.

Between 1958 and 1962, physicians Olive W. Smith, George V. Smith, and Robert W. Kistner performed experiments that demonstrated the effects of the drugs MER-25 and clomiphene citrate on the female human body. MER-25 and clomiphene citrate are drugs that affect estrogen production in women. At the time of the experiment, researchers did not know which organ or organs the drugs affected, the ovaries and/or the anterior pituitary gland. To determine that, the physicians reviewed nine of their own previous studies in women in which they measured the urinary output of hormones after the administration of either drug. Based on their examination the researchers concluded that MER-25 appeared to influence the anterior pituitary gland in the brain to produce a response in the ovaries and that clomiphene citrate appeared to act on the ovaries. Their results provided early evidence about the mechanisms of both drugs. Later, clomiphene citrate became a common fertility drug.

Progestin is a synthetic form of progesterone, a naturally occurring hormone, which plays an important role in the female reproductive cycle. During the 1950s two types of progestin that were later used in birth control pills were created, norethindrone and norethynodrel. In 1951 Carl Djerassi developed norethindrone at Syntex, S.A. laboratories located in Mexico City, receiving a patent on 1 May 1956. In 1953 Frank Colton developed norethynodrel at G.D. Searle and Company laboratories located in Chicago, receiving a patent on 29 November 1955. These two types of synthetic progesterone are important to the history of embryology because they facilitated the development and creation of the birth control pill, which changed the way people viewed birth control and revolutionized women's birth control methods.