The official Democratic platform for every cycle from 1976 to 2000 (except 1984-88 when abortion was not mentioned at all) explicitly acknowledged that abortion was controversial, that abortion opponents were welcome in the party, and that decreasing the number of abortions that are necessary is a worthy goal. The issue got more polarized when it became clear that no compromise or detente less than overturning Roe v. Wade would ever be accepted. I don't know of any specific pledges not to expand abortion access, again because the Hyde amendment prevented any proposals to expand abortion access.