Luteal phase
Encyclopedia
The luteal phase is the latter phase of the menstrual cycle
(in humans and a few other animals) or the estrous cycle
(in other placental mammals
). It begins with the formation of the corpus luteum
and ends in either pregnancy or luteolysis
. The main hormone associated with this stage is progesterone
, which is significantly higher during the luteal phase than other phases of the cycle. Some sources define the end of the luteal phase to be a distinct "ischemic phase".
and LH
cause the remaining parts of the dominant follicle to transform into the corpus luteum
. It continues to grow for some time after ovulation and produces significant amounts of hormones, particularly progesterone, and, to a lesser extent, estrogen
. Progesterone plays a vital role in making the endometrium
receptive to implantation of the blastocyst
and supportive of the early pregnancy; it also has the side effect of raising the woman's basal body temperature
.
Several days after ovulation, the increasing amount of estrogen produced by the corpus luteum may cause one or two days of fertile cervical mucus, lower basal body temperatures, or both. This is known as a "secondary estrogen surge".
The hormones produced by the corpus luteum also suppress production of the FSH and LH that the corpus luteum needs to maintain itself. With continued low levels of FSH and LH, the corpus luteum will atrophy. The death of the corpus luteum results in falling levels of progesterone and estrogen. These falling levels of ovarian hormones cause increased levels of FSH, which begins recruiting follicles for the next cycle. Continued drops in levels of estrogen and progesterone trigger the end of the luteal phase: menstruation and the beginning of the next cycle.
The average length of the human luteal phase is fourteen days (2 weeks). Between ten and sixteen days is considered normal, although luteal phases of less than twelve days may make it more difficult to achieve pregnancy. While luteal phase length varies significantly from woman to woman, for the same woman the length will be fairly consistent from cycle to cycle.
The loss of the corpus luteum can be prevented by implantation of an embryo
: after implantation, human embryos produce human chorionic gonadotropin
(hCG). hCG is structurally similar to LH and can preserve the corpus luteum. Because the hormone is unique to the embryo, most pregnancy test
s look for the presence of hCG. If implantation occurs, the corpus luteum will continue to produce progesterone (and maintain high basal body temperatures) for eight to twelve weeks, after which the placenta
takes over this function.
of birth control
works primarily by preventing ovulation
, but is also known to cause LPD.
LPD is a spectrum. There is unruptured luteinized follicle syndrome (ULFS), short luteal phases (e.g. 9 days instead of 14) and follicular nonresponsiveness to hCG
. The second two varieties can be stabilized by taking high dose progesterone suppositories or injections till one gets a positive pregnancy test, and then continuing for another 8-10 weeks until placenta is self-sufficient. Some people have seen normalisation with high dose B6.
ULFS can be treated by high dose hCG at ovulation, or by IVF
Diagnostics are by ultrasound, day 21 progesterone test, and length of luteal phase
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....
(in humans and a few other animals) or the estrous cycle
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...
(in other placental mammals
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
). It begins with the formation of the corpus luteum
Corpus luteum
The corpus luteum is a temporary endocrine structure in mammals, involved in production of relatively high levels of progesterone and moderate levels of estradiol and inhibin A...
and ends in either pregnancy or luteolysis
Luteolysis
Luteolysis is the structural and functional degradation of the corpus luteum , which occurs at the end of the luteal phase of both the estrous and menstrual cycles in the absence of pregnancy. In domestic animals, luteolysis is inititated by the hormones prostaglandin F2alpha and oxytocin...
. The main hormone associated with this stage is progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
, which is significantly higher during the luteal phase than other phases of the cycle. Some sources define the end of the luteal phase to be a distinct "ischemic phase".
Hormonal events
After ovulation, the pituitary hormones FSHFollicle-stimulating hormone
Follicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone act...
and LH
Luteinizing hormone
Luteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
cause the remaining parts of the dominant follicle to transform into the corpus luteum
Corpus luteum
The corpus luteum is a temporary endocrine structure in mammals, involved in production of relatively high levels of progesterone and moderate levels of estradiol and inhibin A...
. It continues to grow for some time after ovulation and produces significant amounts of hormones, particularly progesterone, and, to a lesser extent, estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
. Progesterone plays a vital role in making the endometrium
Endometrium
-Function:The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a...
receptive to implantation of the blastocyst
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...
and supportive of the early pregnancy; it also has the side effect of raising the woman's basal body temperature
Basal body temperature
Basal body temperature is the lowest temperature attained by the body during rest . It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature...
.
Several days after ovulation, the increasing amount of estrogen produced by the corpus luteum may cause one or two days of fertile cervical mucus, lower basal body temperatures, or both. This is known as a "secondary estrogen surge".
The hormones produced by the corpus luteum also suppress production of the FSH and LH that the corpus luteum needs to maintain itself. With continued low levels of FSH and LH, the corpus luteum will atrophy. The death of the corpus luteum results in falling levels of progesterone and estrogen. These falling levels of ovarian hormones cause increased levels of FSH, which begins recruiting follicles for the next cycle. Continued drops in levels of estrogen and progesterone trigger the end of the luteal phase: menstruation and the beginning of the next cycle.
The average length of the human luteal phase is fourteen days (2 weeks). Between ten and sixteen days is considered normal, although luteal phases of less than twelve days may make it more difficult to achieve pregnancy. While luteal phase length varies significantly from woman to woman, for the same woman the length will be fairly consistent from cycle to cycle.
The loss of the corpus luteum can be prevented by implantation of an embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
: after implantation, human embryos produce human chorionic gonadotropin
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...
(hCG). hCG is structurally similar to LH and can preserve the corpus luteum. Because the hormone is unique to the embryo, most pregnancy test
Pregnancy test
A pregnancy test attempts to determine whether or not a woman is pregnant.These markers are found in urine and blood, and pregnancy tests require sampling one of these substances. The first of these markers to be discovered, human chorionic gonadotropin , was discovered in 1930 to be produced by...
s look for the presence of hCG. If implantation occurs, the corpus luteum will continue to produce progesterone (and maintain high basal body temperatures) for eight to twelve weeks, after which the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
takes over this function.
Luteal phase defect
Luteal phase defect (LPD) occurs when the luteal phase is shorter than normal, progesterone levels during the luteal phase are below normal, or both. LPD is believed to interfere with the implantation of embryos. The lactational amenorrhea methodLactational Amenorrhea Method
The lactational amenorrhea method is a method of avoiding pregnancies which is based on the natural postnatal infertility that occurs when a woman is amenorrheic and fully breastfeeding...
of birth control
Birth control
Birth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
works primarily by preventing 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...
, but is also known to cause LPD.
LPD is a spectrum. There is unruptured luteinized follicle syndrome (ULFS), short luteal phases (e.g. 9 days instead of 14) and follicular nonresponsiveness to hCG
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...
. The second two varieties can be stabilized by taking high dose progesterone suppositories or injections till one gets a positive pregnancy test, and then continuing for another 8-10 weeks until placenta is self-sufficient. Some people have seen normalisation with high dose B6.
ULFS can be treated by high dose hCG at ovulation, or by IVF
Diagnostics are by ultrasound, day 21 progesterone test, and length of luteal phase