I remember hearing this from a client a long time ago and it popped back into my head again today when another teacher asked for some advice on Tokophobia - the dread & fear of pregnancy and childbirth that some women may experience.
Empirical evidence shows that women want and benefit from continuity of carer. The Cochrane review (2016) found that women who received midwife-led continuity of care were less likely to experience preterm births or lose their baby in pregnancy or in the first month following birth.
A birth plan (or proposal if you prefer) stops you from going in blind, or at the whim of others. It doesn't need to be set in stone but can act as a learning experience, a guide or a steel beam to your beliefs and hopes around the birth you wish to have.
Do you want to find out the sex of your baby? Because there is a fair chance that your sonographer will be able to tell you at this point. As one rather amusing sonographer said to me once...hamburger or snail?