The 65-year-old actress - who has a 26-year-old daughter, Eva, with former partner Franco Amurri - admitted after being diagnosed with severe endometriosis, a common cause of infertility, she struggled to fall pregnant until she visited the 300-year-old steps in the summer of 1984.
She said: "If anyone out there`s having trouble getting pregnant, go to Italy. Have a summer and don`t worry about it and eat and drink and ... f**k, and you`ll probably get pregnant. And that`s what happened with Eva on the Spanish Steps.
"That`s where Eva was conceived, on the Spanish steps?"
Speaking about her diagnosis with endometriosis as a young woman, Susan explained it was a "devastating" experience to learn she might not become a mother naturally.
During a `Lucid Conversations` talk with Alan Cumming in New York, which sees the actor host a monthly chat with his celebrity pals, she said: "I had been put in the hospital and they said I had very severe endometriosis, which is a condition that a lot of women have.
"It`s one of these not diagnosed conditions that can be quite, quite devastating."