The reason is the spread of the virus Zeke and his potential danger to the unborn child. Center for control and prevention of diseases under the Ministry of health advised pregnant women protostars from the trip to the Olympics in the center of an epidemic of zika virus.
Yet the Agency does not deny the possibility of sexual transmission of the virus. Therefore, from sex in Rio de Janeiro, experts also advise to refuse. In the U.S. there have been two confirmed cases of disease transmission through sexual contact.
Note that Russia has nothing to fear. The disease is transmitted exclusively Zeke mosquitoes of the genus Aedes, which are in the CIS zone. Now cases of the virus recorded in 39 countries. The danger the disease poses to pregnant women. Virus infection can cause irreversible brain damage of the fetus and the development of hydrocephalus.