There is a custom that some people follow not to permit a new bride or groom during the week after their wedding to attend somebody else’s wedding. For example, according to this custom, a bride would not be allowed to attend the wedding of a friend who gets married during the week of her Sheba Berachot. The reason for this custom is the concern for an "Ayin Ha’ra" (evil eye) that might be triggered by the sight of two new grooms or two new brides together. By the same token, this custom forbids women who just gave brith to attend weddings, as the sight of new mother with a bride could arouse an "Ayin Ha’ra."
Hacham Ovadia Yosef noted that there is no Halachic source at all for this custom, and therefore new brides and grooms and pregnant women who attend weddings have no reason for concern. He adds that even those who do follow this practice allow brides to attend weddings if she exchanges her hairpin with the bride getting married at that wedding, as this negates the possible effects of the "Ayin Ha’ra." Therefore, if one follows this custom, he or she may certainly employ this method to eliminate any concern. This ruling is codified in the work Mishnat Yehoshua (p. 49; listen to audio recording for precise citation).
