To be clear, the Court of Appeal doesn't say that the trial court is required to make such an order; only that it may permissibly do so in its discretion. Moreover, here, the mother allegedly agreed to pay half of the IVF costs -- though the Court of Appeal holds that this agreement is only one of the various factors that the trial court might consider in exercising its discretion. (Accordingly, it may well be that, in a different case, a mother might perhaps be permissibly ordered to reimburse these costs even if she never agreed to do so.)
The Court of Appeal holds that the relevant statute authorizes such an order, and it's easy to see why. Section 7637 of the Family Code provides: "The judgment or order may direct the parent to pay the
reasonable expenses of the mother’s pregnancy and confinement.” Well, the costs of IVF do indeed facially seem to be part of the "reasonable expenses of the mother's pregnancy." So you can see why the Court of Appeal holds that the statute means what it says.
Mind you, sometimes, we create public policy exceptions to otherwise clear statutory mandates. For example, one of the topics we discuss in my seminar is whether a parent can sue the other parent for fraudulently saying they're on birth control when they're not, and thereby recover the expenses that the defrauded parent was required to pay for the child. There's a rule against fraud, of course, but lots of cases hold that our public policy desire for child support, or other social principles, trump the usual rule in this context. You could see a similar argument here, and one might argue that we don't want fathers being able to sue for IVF repayments because it might reduce (or at least offset) child support payments made to the mother, it might be inequitable since both parties consented to the creation of the child (somewhat akin to an "assumption of the risk" argument), etc.
But, at least for now, repayment for half of the expenses of IVF is on the table.
