One way to interpret pon farr is that Vulcans only have sex once every seven years. However, TOS writer and continuity story editor D.C. Fontana once explained that pon farr is not the only time Vulcans feel romantic attraction, sexual desire, or engage in sexual activity:
"Vulcans mate normally any time they want to. However, every seven years you do the ritual, the ceremony, the whole thing. The biological urge. You must, but any other time is any other emotion – humanoid emotion – when you're in love. When you want to, you know when the urge is there, you do it. This every-seven-years business was taken too literally by too many people who don't stop and understand. We didn't mean it only every seven years. I mean, every seven years would be a little bad, and it would not explain the Vulcans of many different ages which are not seven years apart." – D.C. Fontana (Captains' Logs: The Unauthorized Complete Trek Voyages)
Memory Alpha, Pon farr
A common misconception associated with the series (and Spock in particular) is that Vulcans only have sex once every seven years. However, pon farr is not coincident with the sex lives of Vulcans, and they are able to have intercourse without the affliction, and thus more than once every seven years. Star Trek: The Original Series writer and continuity story editor D. C. Fontana explains that pon farr is not the only time that Vulcans feel sexual desire or engage in sexual activity:
Wikipedia, Pon Farr, In Star Trek canon
Vulcans can have sex during other times aside from Pon farr.