Tina Nevill of Essex, England, holds Poppy, who was conceived by in vitro fertilization. The U.K.'s health system records all IVF cycles performed in the country. Barcroft Media/Landov hide caption

itoggle caption Barcroft Media/Landov

Human embryos under a microscope at an IVF clinic in La Jolla, Calif. Sandy Huffaker/Getty Images hide caption

itoggle caption Sandy Huffaker/Getty Images