I don't suppose you have an HSA?
You can always withdraw your contributions (not gains) from Roth IRAs without tax or penalty.
You can withdraw from an IRA for any medical expenses over 7.5% of AGI. At least that's my interpretation of
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-tax-on-early-distributions -- you'll want to make sure IVF counts in case there's some restriction on elective procedures.
Since you can't get money back into retirement accounts, a home equity loan seems like a decent idea if you can afford the payment. Remember that the interest will not be tax deductible under the new tax bill.
The only type of loan you can take against retirement accounts is a 401(k) loan if your employer's plan allows it. You'll need to look at your specific employer's policy to find out how that works for you. You usually have to pay back the whole thing if you leave employment, although the tax bill change it so they now have to give you at least until October of the year following when you stopped work.
Looks like you can undo an IRA contribution as long as you do it by the tax filing deadline for the year of the contribution:
https://finance.zacks.com/can-ira-contributions-reversed-same-year-2098.html. Before you do this consider the tax implications of greater income last year vs greater income in 2018 since not contributing to your 401(k) in 2018 is effectively the same (in terms of reduced balance) as undoing the 2017 contribution. Of course, on the one hand spreading out the reduced tax deferment across years could help, and on the other your tax liability will likely be lower in 2018 thanks to the lower brackets. While I was writing this I see that MDM replied with the idea of recharacterizing the contribution to Roth, then withdrawing that, which I had thought of as well before finding the zacks article, but which seems to contradict the possibility of undoing contributions, so make sure you find more evidence to corroborate the zacks article (or talk with the administrator as they should know) before relying on it, because MDM is usually right. Even if undoing is possible, recharacterizing might be a better option since it keeps the money in a Roth IRA if you end up going another route and not needing it.
Worst case scenario, you can always withdraw and pay the 10% penalty.
I'd probably lean towards one of the loan options before one of the withdrawal or not contributing options since you can pay the loan back, but you can't get money back in accounts. Of course this assumes that you can afford to pay the loans back without reducing future contributions, otherwise it has the same effect plus the hassle and possibly added expense of taking out the loans. Also consider whether you're the type of person who will be stressed more by the loans than withdrawing from the accounts. I don't know much about IVF, but I imagine lower stress increases the likelihood of success, so may as well do everything you can to reduce the number of rounds you have to do.
Good luck!
Edit: to followup on Freedom2016's post, here are the states that require some type of coverage:
https://attainivf.attainfertility.com/ivf-insurance