Can a QTIP be established before a couple gets married?

A QTIP-style trust can be created before a couple gets married, but it will not qualify for the marital deduction against gift taxes unless it is not funded until after the marriage is final. The transfer to a QTIP trust, in other words, will not accomplish what it's normally supposed to accomplish unless the beneficiary of the QTIP transfer is actually the spouse of the transferor. I'm not sure what you mean by your reference to "a QTIP trust regarding [your] fiance's retirement assets," however. The QTIP reference does not make sense in this context, and I'm not sure what you are thinking would happen. If you are not comfortable signing a prenup, then that's your decision, but a QTIP trust does not substitute for a prenuptial agreement in any way, shape, or form. You may want to have a consultation with a good family law attorney to discuss your concerns about the prenup and what your ideas with regard to the retirement account assets are. An estate planning consultation may also be helpful. Best wishes on your pending marriage.