Here is the definition you linked to:
Pregnancy
Definition
The period from conception to birth. After the egg is fertilized by a sperm and then implanted in the lining of the uterus, it develops into the placenta and embryo, and later into a fetus. Pregnancy usually lasts 40 weeks, beginning from the first day of the woman's last menstrual period, and is divided into three trimesters, each lasting three months.
Here is the definition of Conception:
Conception is not the same thing as
fertilization.
Contra
ceptives are for the prevention of pregnancy. Some forms of contraception work by preventing fertilization (preventing sperm meeting egg,) while other forms of contraception work by preventing conception (preventing blastocyte from implanting.) Fertilization does not necessarily lead to conception. There are many situations that can cause conception to be difficult to achieve, even though fertilization has occurred.