Throughout menstrual cycle

The uterus frequently contracts throughout the entire menstrual cycle

Menstrual cycle

The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

, and these contractions have been termed endometrial waves or contractile waves. These appear to involve only the sub-endometrial layer of the myometrium

Myometrium

The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells , but also of supporting stromal and vascular tissue...

. In the early follicular phase

Follicular phase

The follicular phase is the phase of the estrous cycle, during which follicles in the ovary mature. It ends with ovulation. The main hormone controlling this stage is estradiol....

, these contractions occur once or twice per minute and last 10–15 seconds with a low amplitude of usually 30 mmHg. The frequency increases to 3–4 per minute towards ovulation

Ovulation

Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...

. During the luteal phase

Luteal phase

The luteal phase is the latter phase of the menstrual cycle or the estrous cycle . It begins with the formation of the corpus luteum and ends in either pregnancy or luteolysis...

, the frequency and amplitude decrease, possibly to facilitate any implantation.

If implantation does not occur, the frequency remains low, but the amplitude increases dramatically to between 50 and 200 mmHg producing labor-like contractions at the time of menstruation

Menstruation

Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...

. These contractions are sometimes termed menstrual cramps, although that term is often used for menstrual pain in general. These contractions may be uncomfortable or even painful, but they are generally significantly less painful than contractions during labour. A hot water bottle or exercising has been found to help.

A shift in the myosin expression of the uterine smooth muscle has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle.

In childbirth

In obstetrics

Obstetrics

Obstetrics is the medical specialty dealing with the care of all women's reproductive tracts and their children during pregnancy , childbirth and the postnatal period...

, a contraction may refer specifically to the motion of the uterus

Uterus

The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...

 as part of the process of childbirth

Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...

. Contractions, and labour in general, is one condition that releases the hormone oxytocin

Oxytocin

Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...

 into the body. Contractions become longer as labour intensifies.

Prior to actual labour, women may experience Braxton Hicks contractions, sometimes known as "false labour."

Since every pregnancy is different, a doctor, midwife or other competent professional should always be consulted before any action is taken to reduce the pain. Some popular methods may be harmful to the mother and/or the baby, or may actually worsen the pain or lengthen the labour.

In orgasm

The uterus and vagina contract during female orgasm to encourage male semen to reach the fallopian tubes. These contractions may not be noticed by all women; pregnant women are more likely to notice these contractions by late 2nd and 3rd trimesters.