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Two researchers have launched a study to determine whether Covid-19 mRNA vaccines cause abnormal periods such as heavy bleeding.

Dr. Kathryn Clancy and Dr. Katherine Lee say they launched the study when they both experienced heavy menstrual bleeding after taking the vaccines.

When Clancy and Lee asked their Twitter followers to describe their abnormal menstrual cycles after taking the vaccines, hundreds of women replied.

Clancy and Lee are now compiling data from a questionnaire asking women to describe their abnormal periods. As of Monday, more than 25,000 women have completed the questionnaire, Dailymail.com reported.

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In a series of tweets in February, Clancy discussed her heavy menstrual bleeding after taking the first shot of Moderna.

"I'm curious whether other menstruators [sic] have noticed changes too?" she wrote.

"I'm a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I'm in my 20s again. I'm on day 3 of my period and am still swapping out extra long overnight pads a few times a day. Typical for me at this time is maybe one or two regular pads."

On April 7, Clancy tweeted out a link to a survey in which women could document their menstrual irregularities.

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Thrombocytopenia, or low blood platelets, was among the adverse effects reported to the Vaccine Adverse Event Reporting System (VAERS) system.

Low blood platelets causes abnormal bleeding, weakness and fatigue.

Experts say Pfizer, Moderna and Johnson & Johnson did not report any menstrual irregularities during their relatively short clinical trials.

They say it's too early to suggest a link between heavy cycles and vaccinations until a larger study is conducted.

The Food & Drug Administration approved the mRNA vaccines on an emergency basis.

The FDA approval allowed pharmaceutical companies to forego longterm studies of their vaccines.

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A blood disorder that affects the platelets has been reported in at least 2 dozen people who received Covid-19 mRNA vaccines in the United States.

Thrombocytopenia is among the adverse effects reported to the Vaccine Adverse Event Reporting System (VAERS) system, which is jointly run by the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration.

Thrombocytopenia is an abnormally low platelet count in the blood. A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.

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Low platelets causes abnormal bleeding, weakness and fatigue.

Signs and symptoms of low platelet count are frequent nosebleeds, bleeding gums, bruising all over the body, longer periods in women, small red or purple spots on the skin, spontaneous bleeding under skin, blood filled blisters inside the mouth.

MSN reports that by the end of January, 32 cases of a decreased platelet count, 14 cases of thrombocytopenia, and 11 cases of immune thrombocytopenia were recorded in people who had received either Pfizer or Moderna COVID vaccines in the U.S.

If you notice any unusual signs of bleeding after getting the mRNA vaccine, contact your doctor or healthcare provider immediately.