While the controversy rages, the medical establishment has accepted PMS as a bona fide condition. According to the most current clinical handbook of psychiatric diagnoses, the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV, published by the American Psychiatric Association in 1994), "at least 75 percent of women report minor or isolated premenstrual changes." The DSM-IV estimates that 20 to 50 percent of menstruating women suffer from some form of PMS (other sources put the number as high as 75 percent), while 3 to 5 percent of women are estimated to suffer from the most severe form of PMS, PMDD, or premenstrual dysphoric disorder.

Symptoms are considered premenstrual if they appear during the luteal phase of the cycle (the 14 days between ovulation and menstrual flow), begin to remit within a few days of menses and are totally absent in the week following menses. To meet the diagnostic criteria for PMDD, a woman must have at least one severe emotional (as opposed to physical) symptom each month, the severity of which must be great enough to have a major negative impact on normal functioning.

Thompson pointed out that Plath unwittingly recorded experiencing on a cyclical basis all of the major symptoms of PMS, as well as many others, including low impulse control, extreme anger, unexplained crying and hypersensitivity. She also suffered many of the physical symptoms associated with PMS, notably extreme fatigue, insomnia and hypersomnia, extreme changes in appetite, itchiness, conjunctivitis, ringing in the ears, feelings of suffocation, headaches, heart palpitations and the exacerbation of chronic conditions such as her famous sinus infections.

Thompson compared Plath's reported mood and health changes with the journals, letters and biographies and found that her symptoms seemed to appear and disappear abruptly on a fairly regular schedule, with clusters of physical symptoms and depressive affect followed by dramatic changes in outlook and overall physical health. Those patterns can be directly linked to the dates of Plath's actual menses, particularly in 1958 and 1959, when she most habitually noted her cycles. Judging from the pattern of Plath's depression and health in late 1952 and in 1953 until her Aug. 24 suicide attempt, Thompson posited that "it seems reasonable to conclude that this suicide attempt was directly precipitated by hormonal disruption during the late luteal phase of her menstrual cycle and secondarily by her loss of self-esteem at being unable to control her depression."

Thompson showed that a well-known journal entry from Feb. 20, 1956, is clearly traceable to Plath's menses, to which she refers directly a few days later. The journal fragment takes on new meaning in light of having been written during the physically and emotionally debilitating luteal phase of Plath's cycle: "Dear Doctor: I am feeling very sick. I have a heart in my stomach which throbs and mocks. Suddenly the simple rituals of the day balk like a stubborn horse. It gets impossible to look people in the eye: corruption may break out again? Who knows. Small talk becomes desperate. Hostility grows, too. That dangerous, deadly venom which comes from a sick heart. Sick mind, too." On Feb. 24, the same day she notes in her journal that she has a sinus cold and "atop of this, through the hellish sleepless night of feverish sniffling and tossing, the macabre cramps of my period (curse, yes) and the wet, messy spurt of blood," Plath wrote a letter to her mother blaming her dark mood on her physical health: "I am so sick of having a cold every month; like this time, it generally combines with my period."

By perhaps fateful coincidence, Plath's Feb. 24, 1956, period is the first she mentions specifically in her entire journal; the next day, she met her future husband, Ted Hughes, at a party. Thompson explains that disruptions in the menstrual cycle, particularly those caused by pregnancy and breast-feeding, can have a dramatic hormonal impact on PMS sufferers; in the two and a half years between June 1959 and January 1962, Plath experienced three pregnancies, one of which ended in miscarriage. In addition, she breast-fed both of her babies for lengthy periods (10 months for Frieda, about eight months for Nick, according to letters to her mother) and probably experienced very few normal menstrual cycles during that time.

Wrote Thompson, "Her reproductive history almost guaranteed some form of extreme emotional disruption once she began menstruating again after the birth of her second child, with a probable further disruption following the cessation of breastfeeding. Like many women with PMS, Plath seems to have experienced relief from cyclical symptoms during the last two trimesters of pregnancy and to have suffered from lengthy postpartum depressions." That last disruption, in the fall of 1962 when she weaned Nicholas, would have coincided with the writing of the "Ariel" poems.

Thompson's close reading of the "Ariel" poems in terms of Plath's menses noted the discernibly cyclic pattern of rise and fall in mood and tone in the poems as well as their many images and themes of barrenness, fertility, psychic pain, bleeding and relief, always controlled by the overseeing influence of the inspiring but uncaring and all-powerful moon goddess. "If I could bleed, or sleep!" Plath wrote in "Poppies in July," shortly after the discovery of her husband's adultery in July 1962, presumably a time when Plath was not just emotionally distraught but also experiencing suppressed menstruation because of her young baby's breast-feeding.

By the fall of 1962, the poems (which Plath carefully dated as they were completed) seem to follow a pattern of metaphorical renewals and optimistic transformations for roughly two to three weeks of artistic production, then jagged, seething accusations and aggression for a couple of weeks. (As can be seen in the unabridged journals, for at least two years prior to the beginning of her first pregnancy in 1959, Plath's menstrual cycles had regulated to cycles of 30 to 35 days, which corresponds with the timing of the "cycles" of the Ariel poems.)

Thompson's article closes on a note of tragic irony: Dalton, who had coined the term "premenstrual tension" in 1954 and who was the only physician successfully treating women for severe PMS in 1963, practiced in London. Plath, who had moved to London from her country home in December 1962, "died in the only city in the world where she could have received effective medical treatment."

Thompson's PMS theory has been largely ignored by Plath scholars. But it immediately gained two important supporters: Anne Stevenson, Plath's controversial biographer, and Olwyn Hughes, Plath's former sister-in-law, whose letters were published in a subsequent issue of Triquarterly. Though oddly defensive in tone, Stevenson's letter does commend Thompson for her "invaluable contribution to Plath scholarship ... Certainly no future study of Plath will be able to ignore the probable effects of premenstrual syndrome on her imagination and behavior." And it states that she wishes she had been able to utilize Thompson's insights in the writing of her own work on Plath.

A letter from Olwyn Hughes also congratulates Thompson for her scholarship, but unlike Stevenson, Hughes practically stumbles over herself in amazement at the PMS theory. Hughes, who was quoted in Janet Malcolm's book "The Silent Woman: Sylvia Plath and Ted Hughes" as characterizing her long-dead sister-in-law as "pretty straight poison," wrote to Thompson: "It is quite a shock to digest all this -- after thinking for so long that Sylvia's subconscious mind was her prison, and to suddenly realise it may well have been in part, or wholly, her body. But it certainly tallies with Ted's mentions -- he has always felt some chemical imbalance was involved."

Hughes further points out that Ted Hughes had spoken of Plath's ravenous appetite just prior to her periods and asks, "I wonder if that is a known characteristic of PMS?" (According to the PMS literature, it is.) But most tellingly, Olwyn Hughes explains that "one of the reasons I was so bowled over by your piece is that Sylvia's daughter, very like her physically, suffers quite badly from PMS but is, in these enlightened times, aware of it and treats it."

Dr. Glenn Bair, one of the leading experts on PMS treatment and research in the United States, confirmed to Salon that PMS is typically passed from mother to daughter. In a rare interview about her parents, Frieda Hughes told the Manchester Guardian in 1997 that after the "collapse of her health," including extreme fatigue and gynecological problems, she underwent a hysterectomy in her 30s.

Actress Frances McDormand reads Sylvia Plath's "The Bell Jar"