A WOMAN infected with HIV is more likely to pass the virus on to her male partner if they have unprotected sex during her period than if they avoid this time. And an infected man is more likely to infect his female partner if he has had sexually transmitted diseases other than AIDS, such as herpes or genital warts, in the past five years. These are among the conclusions of a new study of risk factors in the transmission of HIV between heterosexuals. Isabelle De Vincenzi, an epidemiologist for the European Study Group of the World Health Organization’s Collaborating Centre on AIDS, based in Paris, announced her team’s initial results at a conference in Chamonix last week. The researchers studied 332 heterosexual couples from the Netherlands, France, Spain, Italy, Belgium, Germany and Greece and interviewed each member of each couple separately about their histories and sexual practices with their partner. ..