Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term.
http://en.wikipedia.org/wiki/Infertility
THE FIRST COMMANDMENT that God gave to Adam and Eve pertained to their potential for parenthood as husband and wife. We declare that God’s commandment for His children to multiply and replenish the earth remains in force. We further declare that God has commanded that the sacred powers of procreation are to be employed only between man and woman, lawfully wedded as husband and wife.
WE DECLARE the means by which mortal life is created to be divinely appointed. We affirm the sanctity of life and of its importance in God’s eternal plan.
http://www.lds.org/topics/family-proclamation
This generates an initial question of "If God's plan is inherently that male and female come to earth to procreate, how come He sends males and females here who cannot, naturally, follow the plan?"