technically it takes just one sperm to fertilize an egg and achieve a pregnancy but for each sperm that reaches and fertilizes an egg there are many millions that don't. the average ejaculation contains close to 100 million sperm and according to the world health organization men who have fewer than 20 million sperm per milliliter of semen may have difficulty conceiving. why do you need so many sperm if it takes just one to make a baby? because the journey from the vagina to the fallopian tubes through which the eggs travel from the ovaries to the uterus is an arduous one that few sperm survive. for those that complete the trip penetration of the egg is far from a sure thing. the egg is covered by a thick layer that makes fertilization more difficult. experts believe this process may be nature's way of allowing only the healthiest sperm to fertilize the egg thereby providing the greatest chances for a healthy baby.
how many sperm do you need to achieve a pregnancy?