Eggs may be more vulnerable to freezing than embryos, but that's just one factor that affects the odds of having a baby with frozen eggs. Jean-Paul Chassenet/Science Source hide caption

itoggle caption Jean-Paul Chassenet/Science Source

Heroin sold in the U.S., like this dose confiscated in Alabama last fall, is often cut with other drugs. Tamika Moore/AL.com/Landov hide caption

itoggle caption Tamika Moore/AL.com/Landov

Michael Arnott, of Cambridge, Mass., says he used to have trouble staying awake on long drives. Sleep specialists discovered he has obstructive sleep apnea, though not for the most common reasons — he isn't overweight, and doesn't smoke or take sedatives. M. Scott Brauer for NPR hide caption

itoggle caption M. Scott Brauer for NPR

Frozen sperm straws and embryos are stored in liquid nitrogen, in a process known as cryopreservation. One question confronting the courts: Should embryos such as these be treated as property, or as children subject to custody action? Veronique Burger/Science Source hide caption

itoggle caption Veronique Burger/Science Source
Katherine Streeter for NPR

Bacillus subtilis may look like pasta under the microscope, but the bacteria are common in the gut of humans. Could the microbes be contributing to our belly fat? Too soon to tell, scientists say. BSIP/UIG via Getty Images hide caption

itoggle caption BSIP/UIG via Getty Images