Though it's been tried for millennia, it is of course as yet unproven that crying works as birth control. But laughing may help fertility.
In a quasi-randomized study, researchers at Assaf Harofeh Medical Center in Zrifin, Israel found that the pregnancy rate following in vitro fertlization and embryo transfer was more than 16% higher among women who were visited immediately after embryonic transfer by a medical clown. As reported in "The Effect of Medical Clowning on Pregnancy Rates after In Vitro Fertilization and Embryo Transfer (IVF-ET)" the clown performed 12-15 minute routines of jokes, tricks, and magic at each woman's bedside.
The researchers point out that the immune benefits of humor have long been understood, and that the beneficial effect of stress reduction on successful egg implantation has been demonstrated recently in rats. They also suggest that, even though their method requires one clown per IVF mom, it's a cheaper and more successful intervention than many other stress reduction techniques that fertility clinics have historically advocated.