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= Lactational Amenorrhea =

Hormonal Pathways and Neuroendocrine Control
Breastfeeding delays the resumption of normal ovarian cycles by disrupting the pattern of pulsatile release of GnRH from the hypothalamus and hence LH from the pituitary. The plasma concentrations of FSH during lactation are sufficient to induce follicle growth, but the inadequate pulsatile LH signal results in a reduced estradiol production by these follicles. When follicle growth and estradiol secretion does increase to normal, lactation prevents the generation of a normal preovulatory LH surge and follicles either fail to rupture, or become atretic or cystic. Only when lactation declines sufficiently to allow generation of a normal preovulatory LH surge to occur will ovulation take place with the formation of a corpus luteum of variable normality. Thus lactation delays the resumption of normal ovarian cyclicity by disrupting but not totally inhibiting, the normal pattern of release of GnRH by the hypothalamus. The mechanism of disruption of GnRH release remains unknown.

The Suckling Stimulus
Suckling intensity directly correlates with the duration of the amenorrheal period following birth. Suckling intensity has several dynamic components: frequency of suckling, duration of the suckling bout, and duration of suckling in a 24 hour period. It is not clear which of these plays the most critical role in maintaining amenorrhea. Suckling intensity is highly variable across populations. Studies of U.S. and Scottish women show that at least six bouts per day and 60 minutes of suckling in a 24 hour period will typically sustain amenorrhea. !Kung women in Botswana and Gainj women in Papua New Guinea have very frequent, very short suckling bouts of about 3 minutes, 40 to 50 times per day. These two groups also remain amenorrheal for up to two years postpartum.

When an infant suckles, sensory receptors in the nipple send a signal to the anterior pituitary gland in the brain, which secretes prolactin and oxytocin. Prolactin and oxytocin trigger the release (letdown) of milk and its ejection from the nipple in a positive feedback loop. It was previously thought that prolactin hormone, which is released by the anterior pituitary in response to the direct nerve stimulation of suckling, was responsible for creating the hormonal pathways necessary to sustain amenorrhea. Now, however, it seems that this relationship is one of correlation not causation as prolactin levels in the blood plasma are simply an indicator of suckling frequency. Suckling, and the subsequent release of prolactin, is not directly responsible for postpartum infecundity. Rather it is one mechanism that increases milk production, thereby increasing the metabolic cost of breastfeeding to mothers, which contributes to sustained infecundity.

Suckling as proxy indicator of infecundity rather than a direct, hormonal causal factor is supported in studies contrasting the nursing intensity hypothesis, which says that more intense (prolonged, frequent) breastfeeding will result in a longer period of lactational amenorrhea, and the metabolic load model, which posits that maternal energy availability will be the main factor determining postpartum amenorrhea and the timing of the return of ovarian function.

Lactation and Energy Availability
Postpartum ovarian function and the return of fecundity depend heavily on maternal energy availability. This is due to the relatively consistent metabolic costs of milk production across populations, which fluctuate slightly but represent a significant cost to the mother. The metabolic load hypothesis states that women with more available energy or caloric/metabolic resources will likely resume ovarian function sooner, because breastfeeding represents a proportionally lower burden on their overall metabolic function. Women with less available energy experience a proportionally higher burden due to breastfeeding and therefore have less surplus metabolic energy to invest in continued reproduction. The metabolic load model is therefore consistent with the nursing intensity hypothesis, in that more intense nursing increases the relative metabolic burden of breastfeeding on the mother. It also takes into account the overall energy supply of the mother in determining whether she has enough caloric/metabolic resources available to her to make reproduction possible. If net energy supply is high enough, a woman will resume ovarian cycling sooner despite still breastfeeding the current infant.

Infecundity
Amenorrhea itself is not necessarily an indicator of infecundity, as the return of ovarian cycling is a gradual process and full fecundity may occur before or after first postpartum menses. Additionally, spotting or the appearance of first postpartum menses can be a result of either lochia or estrogen withdrawal and not actual ovulation.

Article Evaluation - Wiki Education week 3 exercise
Lactational Amenorrhea: this article is written from the standpoint of using LAM as a form of "natural" birth control which is sanctioned by the Roman Catholic Church. I would like to contribute sections to this article discussing the evolutionary origins of lactational amenorrhea, as well as its physiological consequences and implications.

In our group, I will be responsible for adding to the Physiology section of the article, including the neuroendocrine control of lactational amenorrhea and the role that the suckling stimulus plays in regulating that control.

Sources:

Wood, James. Dynamics of Human Reproduction, chapter 8 - Breastfeeding and Postpartum Infecundability

Article Evaluation


 * Is everything in the article relevant to the article topic? Is there anything that distracted you? - the discussion of the Roman Catholic Church and their views on LAM as a moral/immoral form of birth control seem unnecessary and distracting in a medical context. Conversely, if we include the views of one particular group, could we not include other culture's evaluations of LAM as contraception?
 * Is any information out of date? Is anything missing that could be added? - the Physiology section has a basic explanation of the neuroendocrine controls for LAM but doesn't include much information on the suckling stimulus
 * What else could be improved? - the title of the first section "breastfeeding infertility" is medically and anthropologically inaccurate
 * Is the article neutral? Are there any claims that appear heavily biased toward a particular position? - the bias in question would be looking at LAM purely from a popular standpoint as a form of contraception, not from an evolutionary or medical standpoint as a factor affecting lifetime fertility or birth spacing. It sounds like the article is promoting LAM as a form of birth control
 * Are there viewpoints that are overrepresented, or underrepresented? -LAM in natural fertility populations OTHER THAN Western/European/Catholic populations - ie if we are talking about it as conscious contraception, what other cultures practice this
 * Check a few citations. Do the links work? Does the source support the claims in the article? - links work, one "citation needed"
 * Is each fact referenced with an appropriate, reliable reference? Where does the information come from? Are these neutral sources? If biased, is that bias noted? - in the section on Physiology the sources are scholarly in nature but one source is used multiple times for most of the section.
 * What kinds of conversations, if any, are going on behind the scenes about how to represent this topic? - representing as form of birth control, no discussion of it as a medical/evolutionary phenomenon
 * How is the article rated? Is it a part of any WikiProjects? WikiProject Medicine - rated as start class and low priority
 * How does the way Wikipedia discusses this topic differ from the way we've talked about it in class? - talked about as a form of intentional contraception