1.   Only one sperm fertilizes an egg, but it evidently requires the backup of many millions of others.

2.   It only takes one sperm to fertilize an egg.

3.   The sperm fertilizes the egg.

4.   A single sperm fertilizes an egg.

5.   IVF is, after all, a very delicate process, which only works if the sperm successfully fertilizes the egg inside the petri dish.

6.   The second hormone causes the eggs to pop off the ovary and enter the fallopian tube, where sperm can fertilize them.

7.   The sperm would fertilize the egg while the cytoplasm, they hoped, would allow the embryo to develop.

8.   Their eggs can turn into embryos without being fertilized by sperm.

9.   When sperm carrying the Y chromosome fertilizes an egg it directs the resulting baby to be a male.