An analysis by the UK's health regulator said there was no evidence to support concerns that menstrual disorders and unexpected vaginal bleeding were caused by COVID-19 vaccines.
The Medicines and Healthcare products Regulatory Agency (MHRA) said it would continue to monitor safety data for the use of the vaccines during pregnancy.
The agency said it had carried out a "rigorous evaluation" into reports of changes to menstrual cycles and related symptoms in women who had received a COVID vaccine but concluded that the proportion of people experiencing such conditions was "low in relation to both the number of people who have received COVID-19 vaccines to date and how common menstrual disorders are generally".
It said reported menstrual changes were "mostly transient in nature".
It added: "There is no evidence to suggest that COVID-19 vaccines will affect fertility and the ability to have children."
'Reassuring'
Dr Jo Mountfield, consultant obstetrician and vice president of the Royal College of Obstetricians and Gynaecologists, said: “It is reassuring that the MHRA has investigated reports of suspected side effects of menstrual disorders and unexpected vaginal bleeding and not found any links to the COVID-19 vaccine.
"We recognise that changes to periods can be concerning, but we want to stress that these changes appear to be temporary, and most women's menstrual cycles return to normal after one to two cycles.
"If you do notice any bleeding that is unusual for you, we recommend talking to your doctor."
Yellow Card Reporting
Last week, the MHRA confirmed that it had received 30,304 reactions through the yellow card system relating to a variety of menstrual disorders from women who had received one of the three vaccines currently approved for use in the UK. The reports mentioned heavier than usual periods, delayed periods, and unexpected vaginal bleeding.
In context, this followed approximately 44.8 million COVID vaccine doses administered to women up to August 4 this year.
The MHRA pointed out that despite the uncomfortable or distressing nature of the conditions, period problems were extremely common. Also, stressful life events could disrupt menstrual periods, it said.
Infection with the SARS-CoV-2 virus, and people who have experienced long COVID, could also be affected, according to the regulator.
Dr Mountfield agreed that there was "no evidence that the COVID-19 vaccine will affect a person's fertility, or ability to have children".
COVID Vaccines Recommended for Pregnant Women
In April, the Joint Committee on Vaccination and Immunisation said that pregnant women should be eligible for a COVID vaccine at the same time as the rest of the population.
It advised that pregnant women should receive the Pfizer/BioNTech or Moderna vaccines. However, there was no reason to suggest at this stage that other COVID vaccines were unsafe for them, it said, although more research was needed.
Ongoing research, co-ordinated by St George's Vaccine Institute, is currently investigating COVID vaccines and pregnancy. The Department of Health and Social Care said it had committed £7.5 million to help fund clinical trial data on the best dosing interval for more than 600 participants in the Preg-CoV study.
