Homosexuals who wish to have a child must have recourse to someone other than their regular sexual partner in order to conceive a child. Lesbian couples frequently resort to in vivo artificial insemination with the sperm from a male friend donor, or from the sperm bank of a fertility clinic.
Not all fertility clinics will assist homosexual couples to have children; there are concerns that role models of both sexes are not present in the home for the child, that there will be less parental input from the non-biological parent, and that the child will be unhappy at school because his peers will taunt him about his non-standard family.
Lesbian couples have had children in the USA, the Netherlands and the UK. It is estimated that there might be a few hundred couples in the UK.
Many fertility clinics refuse fertility treatments, including sperm donation, to lesbians on the grounds that they are fertile, and therefore do not need fertility treatments. It's like asking for chemotherapy just to get your hair cut.
A child of lesbian co-parents is very much a wanted child. Obviously there is no such thing as an unwanted pregnancy.