It has always been assumed that having twins was influenced by hereditary factors, but now there is some evidence that whether or not you are a vegetarian can have some bearing on whether you will be more predisposed to having twins.... So if you're hoping for twins, have a read....
http://www.aphroditewomenshealth.com/news/20060422233107_health_news.shtml
http://www.aphroditewomenshealth.com/news/20060422233107_health_news.shtml
