Leave Sex out of It
If you're absolutely desperate to have a girl, you can try shelling out $20,000 or more to guarantee the XX punch. In vitro fertilization—a procedure that carries a hefty price tag—produces a live embryo in the lab after harvesting eggs from mom and sperm from dad. The embryo could potentially have its DNA tested before implantation to find out whether it's got XX or XY chromosomes. Many people find this method to be extremely immoral and unnatural, and some clinics would only do such testing to find serious hereditary defects.
If spending this much money and going through a lot of uncomfortable medical procedures is not part of your plan, you can also guarantee the sex of your child through adoption. Or, trust in luck, folklore, and a smattering of science to get the baby of your dreams. And you may want to eat another grapefruit, while you're at it!