Few women have competed in the Olympics while pregnant, but the suspicion that the Zika virus in mothers is causing birth defects is central to calculations by athletes and others planning travel to Brazil in August for the summer games.
Chief among their concerns is whether Zika, unlike similar mosquito-borne viruses, can be transmitted sexually, or remain latent in the body - possibly presenting a risk for women who become pregnant after the Olympics have ended.
More than a dozen disease experts, in interviews with Reuters, said there is no evidence at this point of long-term risk for future pregnancies. But, given the surprises seen with the virus so far, they said people should remain cautious until studies give scientists a better picture of how the virus works.
They said it would take months or even years of study for definitive answers to questions about Zika's risks.
Public health agencies have urged pregnant women to avoid travel to Zika outbreak areas but have given little guidance for couples planning to start a family.
The virus, which is spreading rapidly through the Americas, has been linked to a spike in microcephaly, a rare birth defect, in Brazil. The condition is defined by unusually small heads in newborns and can cause brain damage.
Zika has not been proven to cause microcephaly, but evidence of an association led the World Health Organisation to declare the outbreak a global health emergency.
The US Centers for Disease Control and Prevention says pregnant women should consider skipping the 2016 Olympics because of the risk of Zika infection. For women who are considering becoming pregnant - and their male partners - the agency recommends consulting their physicians in deciding whether to go to the Games.
The US Food and Drug Administration, however, has suggested a more detailed time frame. It called this week for a six-month delay in all human cell or tissue donations, including of semen and eggs, from people who have had Zika infections or travelled to an outbreak area.
Canada's national health agency on Wednesday advised women who want to get pregnant to wait at least two months after travelling to countries affected by the Zika outbreak.
Eighteen women have competed in modern Olympics while pregnant according to a group of Olympic historians who publish their statistics at Sports-Reference.com. The number includes US beach volleyball gold medallist Kerri Walsh, who was not yet aware she was pregnant when competing in London in 2012.
Some current Olympic hopefuls say they might think twice about the Rio Games if Zika could threaten future pregnancies, and they are hoping for some better answers before the competition begins.
"If things stood as they are right now, I probably would not go," renowned US soccer goalkeeper Hope Solo told CBS last week. "At some point I do want to start a family, and I don't want to be worried."
DeeDee Trotter, a 33-year-old Olympic sprinter and medallist who aims to make the US team again this year, said in an interview she wasn't worried "if the only danger is to women who are pregnant".
That sentiment could change if a prior Zika infection is shown to pose a risk later "when I do decide to have children", she said.
The US Olympic Committee has told athletes that babies may be at risk if the mother is infected with Zika while pregnant, or if she becomes pregnant within an unknown time frame after being infected.
"We have worked to ensure that all potential Olympic and Paralympic athletes are aware of the CDC's recommendations, and we will continue to do so," USOC spokesman Mark Jones said in an emailed statement. "They are the experts."
The CDC says experiencing a Zika infection once likely protects a person from future infection, although that immunity - like so many aspects of Zika - is not yet proven.
Separately, the CDC is investigating at least 14 cases of possible sexual transmission.
Zika was first identified in 1947 in Uganda and previously linked to smaller outbreaks. Many people who are infected show no symptoms, while those who become ill report relatively mild effects of rash or fever.
There is no vaccine or treatment for the virus, which is in the same family as dengue, West Nile virus and yellow fever.
