It sucks, but there’s not a lot that you can do. Society unilaterally decided that once men share genetic material with women, what occurs thereafter is up to the women involved. For obvious reasons, you can’t force a woman to give birth or to get an abortion because she has rightful autonomy and you have no control over her body (and this should always be the case) so your only real option is to tell her how you feel about the matter and explain your reasoning. (Sidenote: I do believe that fathers should be able to abrogate responsibility in an unwanted pregnancy – **T’s & C’s apply!)
If she does go ahead with this, ask yourself how much you’ll be involved with any resulting offspring. Then TELL her what your decision is. As an example:
- If you’re not ready to be a father, explain that point. Explain that you are uninterested in supporting her or being part of any child’s life so she’ll need to be the one to carry 100% of that emotional burden of being the only real parent.
- Raise the fact that you won’t be there for birthdays, Christmas’s or milestones. She’ll be shouldering all of that.
- Having a child against a partner’s wishes is often the death knell in a relationship… What will her life look like as a solo mother? There’s a chunk of society who are less than kind to women who are forced to raise a child alone.
- If you lack funds to actually help support her and child, explain that too. Help her understand what continuing a pregnancy actually looks like if you aren’t involved and just how much of the work she’ll be creating for herself without support. Point out how little she’s going to get in court ordered support (which is all you may be intending to contribute).
- Point out a little more reality – ask her who will babysit the child when she’s trying to work enough hours just to pay the bills after you ghost her?
Some of this might sound really cruel (I get it) but I’ve had conversations with women who are angry that a biological father (‘dead beat dad’)never changed their stance on an unwanted child and refused to have anything to do with the resulting offspring forcing the mother to shoulder 100% of the burden of raising a child. There’s often some bitterness and even rage that absent dads refused to engage with their offspring. (I’m not sure what these women expect? When they opt to continue an unwanted pregnancy, they’re making a unilateral decision about other people’s lives (the father and any subsequent child).
Being upfront and completely honest at this point is critical.
Sometimes newly pregnant women think that a baby will magically turn even a casual couple, into 
a family
… If she’s under the delusion that you’ll be going to Lamaze classes with her and that you’ll eventually all be happy as family unit, then you need to disabuse her of that notion. Don’t let her believe or assume stuff in this area – tell her clearly what your expectations are so that any decision she makes is made with clarity and an understanding of repercussions. Realizing that she’s going to be going it completely alone often happens way too late, often too late to change minds or choose other options.
I’m not saying that this will change her mind but if you truly clarify and crystallize the situation for her, at least any decision she makes will be made with a clear mind and genuine understanding of what she’s walking into.
Then, look at getting a vasectomy → Girlfriends can’t get pregnant if you can’t get them pregnant. These days, vasectomies don’t even need to be reversed if you change your mind about kids. They can harvest sperm straight from the testes: Testicular sperm aspiration (TEST
