Small changes to periods can follow a COVID-19 vaccine but they quickly return to normal, a leading UK menstruation expert has said.

Victoria Male, from Imperial College London, called studies from the US and Norway which tracked women's cycles "reassuring" and she blamed misinformation for fueling concerns over infertility, the BBC reported.

The Medicines and Healthcare products Regulatory Agency has received more than 37,000 reports of unexpected vaginal bleeding, heavier and delayed periods after a COVID-19 jab.

In a British Medical Journal editorial, Male, a lecturer in reproductive immunology, pointed to two studies.

Those who had two doses in the same cycle had a two-day delay but, Male said, that was unlikely among women in the UK, where the gap between doses is at least eight weeks.

The cycle length of one in 10 of the women changed by more than eight days, compared with one in 25 unvaccinated women, but after just two cycles, their periods returned to normal.

Nearly 40 percent saw at least one change, even before being vaccinated, with the most common complaint heavier than normal bleeding.

(This story was published from a syndicated feed. Only the headline and picture has been edited by FIT.)