Diagram illustrating how the uterus lining builds up and breaks down during the menstrual cycle
Menstrual cup filled with menstrual fluid
Half-used blister pack of a combined oral contraceptive. The white pills are placebos, mainly for the purpose of reminding the woman to continue taking the pills.
Amra Padatik India, celebration of Menstrual Hygiene Day in India
Awareness raising through education is taking place among women and girls to modify or eliminate the practice of chhaupadi in Nepal.

Regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina.

- Menstruation

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Menstrual cycle

Series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible.

Menstrual cycle
Progression of the menstrual cycle and some of the hormones contributing to it
An ovary about to release an egg
The anatomy of the uterus
During the menstrual cycle, levels of estradiol (an estrogen) vary by 200 percent. Levels of progesterone vary by over 1200 percent.
A human primary ovarian follicle viewed by microscopy. The round oocyte stained red in the center is surrounded by a layer of granulosa cells, which are enveloped by the basement membrane and theca cells. The magnification is around 1000 times. (H&E stain)

Triggered by falling progesterone levels, menstruation (a "period", in common parlance) is the cyclical shedding of the lining, and is a sign that pregnancy has not occurred.


Time during which one or more offspring develops inside a woman's womb.

A woman in the third trimester of pregnancy
William Hunter, Anatomia uteri humani gravidi tabulis illustrata, 1774
Melasma: pigment changes to the face due to pregnancy
In the later part of pregnancy the uterus takes up much of the abdomen
Timeline of pregnancy, including (from top to bottom): Trimesters, embryo/fetus development, gestational age in weeks and months, viability and maturity stages
Distribution of gestational age at childbirth among singleton live births, given both when gestational age is estimated by first trimester ultrasound and directly by last menstrual period. Roughly 80% of births occur between 37 and 41 weeks of gestational age.
Fertilization and implantation in humans
The initial stages of human embryogenesis
Breast changes as seen during pregnancy. The areolae are larger and darker.
The uterus as it changes in size over the duration of the trimesters
By the end of the second trimester, the expanding uterus has created a visible "baby bump". Although the breasts have been developing internally since the beginning of the pregnancy, most of the visible changes appear after this point.
Pregnant woman in third trimester of pregnancy (last month)
The uterus expands making up a larger and larger portion of the woman's abdomen. At left anterior view with months labeled, at right lateral view labeling the last 4 weeks. During the final stages of gestation before childbirth the fetus and uterus will drop to a lower position.
Linea nigra in a woman at 22 weeks pregnant.
CT scanning (volume rendered in this case) confers a radiation dose to the developing fetus.
A pregnant woman undergoing an ultrasound. Ultrasound is used to check on the growth and development of the fetus.
Giotto di Bondone Visitation, circa 1305
Embryo at 4 weeks after fertilization (gestational age of 6 weeks)
Fetus at 8 weeks after fertilization (gestational age of 10 weeks)
Fetus at 18 weeks after fertilization (gestational age of 20 weeks)
Fetus at 38 weeks after fertilization (gestational age of 40 weeks)
Relative size in 1st month (simplified illustration)
Relative size in 3rd month (simplified illustration)
Relative size in 5th month (simplified illustration)
Relative size in 9th month (simplified illustration)
Anatomical model of a pregnant woman; Stephan Zick (1639–1715); 1700; Germanisches Nationalmuseum
Statue of a pregnant woman, Macedonia
Bronze figure of a pregnant naked woman by Danny Osborne, Merrion Square, Dublin, Ireland
Marcus Gheeraerts the Younger Portrait of Susanna Temple, second wife of Sir Martin Lister, 1620
Octave Tassaert, The Waif aka L'abandonnée 1852, Musée Fabre, Montpellier

Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP).

Premenstrual syndrome

Signs including (enlarged liver and spleen), and symptoms (including headache, and vomiting) of acute HIV infection.

Premenstrual syndrome (PMS) refers to emotional and physical symptoms that regularly occur in the one to two weeks before the start of each menstrual period.


Process by which human breast milk is fed to a child.

A baby breastfeeding
When the baby suckles its mother's breast, a hormone called oxytocin compels the milk to flow from the alveoli (lobules), through the ducts (milk canals), into the sacs (milk pools) behind the areola, and then into the baby's mouth.
Maternal hormone levels during pregnancy and after delivery of the placenta. Estradiol, estriol, progesterone, testosterone, and sex hormone binding globulin (SHBG) all increase throughout the pregnancy, and experience an abrupt drop-off after delivery of the placenta.
Two 25 ml samples of human breast milk. The sample on the left is foremilk, the watery milk coming from a full breast. To the right is hindmilk, the creamy milk coming from a nearly empty breast.
Newborn rests as a caregiver checks its breath sounds with a stethoscope
Example and indicators of a good latch
Example and indicators of a poor, shallow latch
Anterior tongue-tie
Formula and pumped breastmilk side by side. Note that the formula is of uniform consistency and color, while the expressed breast milk exhibits properties of an organic solution by separating into a layer of fat at the top (the "creamline"), followed by the milk, and then a watery blue-colored layer at the bottom.
Manual breast pump
Sign for a private nursing area at a museum using the international breastfeeding symbol
Percentage of babies exclusively breastfed for the first six months of life. Data from 2004 to 2011. 
Macierzyństwo ("Maternity"), a 1902 painting by Stanisław Wyspiański
Ilkhanate prince Ghazan being breastfed
The International breastfeeding symbol
Standing mother breastfeeding her baby, Canjambari, Guinea-Bissau, 1973
Breastfeeding – Cradle hold.
Breastfeeding – Cross cradle position.
Breastfeeding – Football hold.
Breastfeeding – Semi-reclining position.
Breastfeeding – Side-lying position.
Breastfeeding – Supine position.
Breastfeeding – Twins, cross cradle position I.
Breastfeeding – Twins, football or clutch hold.
Breastfeeding – Twins, parallel position II.
Newborn twins being breastfed
Woman breastfeeds 2 year old twins whilst reading them a book.
Woman tandem nurses an infant and a toddler.

Breastfeeding delays the return of menstruation, and in very specific circumstances, fertility, a phenomenon known as lactational amenorrhea.

Mucous membrane

Membrane that lines various cavities in the body of an organism and covers the surface of internal organs.

Histological section taken from the gastric antrum, showing the mucosa of the stomach

In the uterus, the mucous membrane is called the endometrium, and it swells each month and is then eliminated during menstruation.


Inner epithelial layer, along with its mucous membrane, of the mammalian uterus.

Uterus and uterine tubes. (Endometrium labeled at center right.)
Histology of the most superficial layer of the endometrium, consisting of a simple columnar epithelium. H&E stain
High magnification micrograph of decidualized endometrium due to exogenous progesterone (oral contraceptive pill). H&E stain
Low magnification micrograph of decidualized endometrium. H&E stain
Histopathologic and cytopathologic images. (A) proliferative endometrium (Left: HE × 400) and proliferative endometrial cells (Right: HE × 100) (B) secretory endometrium (Left: HE × 10) and secretory endometrial cells (Right: HE × 10) (C) atrophic endometrium (Left: HE × 10) and atrophic endometrial cells (Right: HE × 10) (D) mixed endometrium (Left: HE × 10) and mixed endometrial cells (Right: HE × 10) (E): endometrial atypical hyperplasia (Left: HE × 10) and endometrial atypical cells (Right: HE × 200) (F) endometrial carcinoma (Left: HE × 400) and endometrial cancer cells (Right: HE × 400).
Triple-line endometrium measuring 7mm.
Endometrioid adenocarcinoma from biopsy. H&E stain.
Micrograph of decidualized endometrium due to exogenous progesterone. H&E stain.
Micrograph of decidualized endometrium due to exogenous progesterone. H&E stain.
Micrograph showing endometrial stromal condensation, a finding seen in menses.

The functional layer thickens and then is shed during menstruation in humans and some other mammals, including apes, Old World monkeys, some species of bat, the elephant shrew and the Cairo spiny mouse.


Release of eggs from the ovaries.

Following a surge of luteinizing hormone (LH), an oocyte (immature egg cell) will be released into the uterine tube, where it will then be available to be fertilized by a male's sperm within 12 hours. Ovulation marks the end of the follicular phase of the ovarian cycle and the start of the luteal phase.
Ovulation occurs about midway through the menstrual cycle, after the follicular phase, and is followed by the luteal phase. Note that ovulation is characterized by a sharp spike in levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), resulting from the peak of estrogen levels during the follicular phase.
This diagram shows the hormonal changes around the time of ovulation, as well as the inter-cycle and inter-female variabilities in its timing.
Chance of fertilization by day relative to ovulation

If no conception occurs, the uterine lining as well as the egg will be shed during menstruation.


Long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles.

Acne vulgaris in an 18-year-old male during puberty
Simplistic representation of the formation of acne comedones.
Hair follicle anatomy demonstrating a healthy hair follicle (pictured left), a whitehead or closed comedo (middle picture), and a blackhead or open comedo (pictured right)
Flowchart of the pathological sequence of events leading to acne
The common acne vulgaris treatment benzoyl peroxide cream
Domolene ointment, a mid-1900s medication that was claimed to cure acne

Hormonal activity, such as occurs during menstrual cycles and puberty, may contribute to the formation of acne.


Endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species.

During the menstrual cycle, levels of estradiol (an estrogen) vary by 200 percent. Levels of progesterone vary by over 1200 percent.
Micrograph showing changes to the endometrium due to progesterone (decidualization) H&E stain.
Steroidogenesis, showing progesterone among the progestogens in yellow area.
Progesterone levels across the menstrual cycle in normally cycling and ovulatory women. The horizontal lines are the mean integrated levels for each curve. The vertical line is mid-cycle.
A sample of progesterone.
The Marker semisynthesis of progesterone from diosgenin.
Stigmasterol to progesterone synthesis.
The Johnson total synthesis of progesterone.

Progesterone converts the endometrium to its secretory stage to prepare the uterus for implantation. At the same time progesterone affects the vaginal epithelium and cervical mucus, making it thick and impenetrable to sperm. Progesterone is anti-mitogenic in endometrial epithelial cells, and as such, mitigates the tropic effects of estrogen. If pregnancy does not occur, progesterone levels will decrease, leading, in the human, to menstruate. Normal menstrual bleeding is progesterone-withdrawal bleeding. If ovulation does not occur and the corpus luteum does not develop, levels of progesterone may be low, leading to anovulatory dysfunctional uterine bleeding.

Nonsteroidal anti-inflammatory drug

Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots.

film-coated 200 mg tablets of generic ibuprofen, a common non-steroidal anti-inflammatory drug (NSAID)
NSAID identification on label of generic ibuprofen, an over-the-counter drug (OTC) non-steroidal anti-inflammatory drug.
Burana 600 mg – ibuprofen package
One of the first advertisements for Bayer Aspirin, published in The New York Times in 1917
Kolbe–Schmitt reaction mechanism

Dysmenorrhea (menstrual pain)