• Kentucky and Michigan are the key battlegrounds for abortion in the midterm elections.
• Michigan is voting to amend its constitution in order to protect reproductive rights.
• Kentucky is set to entrench its abortion ban.
• Voters in California and Vermont will also decide whether abortion is protected as a right under their state constitutions.

Follow CNBC's live blog covering Tuesday's midterm elections here.

Voters in California, Kentucky, Michigan and Vermont will decide during the midterm elections whether abortion is protected under their state constitutions.

But Michigan and Kentucky are shaping up as the two biggest battlegrounds on abortion in the midterms. Michigan is poised to become a safe haven of constitutionally protected abortion rights in the Midwest, where access is shrinking.

Kentucky, on the other hand, is set to entrench its abortion ban unless reproductive rights activists pull off an upset victory in the conservative Southern state.

"When changing the constitution, you're thinking about the future — putting in place protections that will last decades and perhaps hundreds of years," said Elizabeth Nash, principal policy associate for state issues at the Guttmacher Institute.

The Supreme Court upended U.S. politics in June when it overturned the landmark Roe v. Wade ruling, which protected abortion as a constitutional right nationwide for nearly 50 years. A dozen states swiftly banned the procedure in the wake of the high court's ruling.

Democrats have made abortion rights central to their campaign to maintain control of Congress and expand their majorities in the midterms. President Joe Biden has vowed to codify Roe v. Wade through law if voters elect more Democratic senators and the party keeps the House.

But Americans appear more concerned with the economy. Just 10% of voters said abortion was the most important issue ahead of Tuesday's midterms while 36% said inflation matters the most, according to a November Quinnipiac Poll.

Right now, Democrats and Republicans are in a dead heat for the Senate, while most analysts believe the GOP will retake the House. This means reinstating abortion rights at the federal level is unlikely in the near term. As a consequence, the battle over abortion will likely continue to play out at the state level for the foreseeable future.

Here's what you need to know about Tuesday's referendums.

Kentucky

In conservative Kentucky, voters will either accept or reject an amendment that explicitly says the state constitution does not recognize abortion as a right.

Kentucky immediately banned abortion after the Supreme Court overturned Roe. It is now a crime for a doctor to perform the procedure, punishable by up to five years in prison. There is an exception for when the woman's life is in danger, but not for victims of rape or incest. A woman cannot be prosecuted for having an abortion.

Democratic Gov. Andy Beshear said the constitutional amendment "would protect and keep in place the most extreme law in the country when it comes to abortion services," according to the Louisville Courier Journal.

Although Kentucky has already banned the procedure, activists who oppose abortion rights want to make it ironclad by ensuring that state courts don't rule against the law one day. State courts initially blocked the ban from going into effect before eventually allowing it to proceed.

The leaders of the Yes to Life campaign in favor of the amendment wrote in a local newspaper in October that the goal was to protect anti-abortion laws from activist judges.

Protect Kentucky Access, the campaign to defeat the amendment, is trying to also convince conservatives who support abortion restrictions that changing the constitution is a step too far.

Kaitlyn Soligan, a spokesperson for the campaign, said people in Kentucky believe strongly in small government and the abortion ban is a clear example of the state going too far.

Soligan said she believes voters will reject the amendment once they understand changing the constitution would entrench a law that bans abortion with no exceptions for even the most extreme situations.

"What we have found to be true across this campaign over the last few months is that the people of Kentucky broadly support exceptions, even when they support restrictions on abortion," Soligan said.

Protect Kentucky Access has spent $4.3 million to defeat the ballot measure, much more than Yes for Life, which has spent about $500,000, according to state campaign filings.

There's no public polling on the Kentucky amendment, so it's not clear which way voters are trending heading into the polls. Kentucky is a conservative state where many people oppose abortion, but this doesn't mean the outcome is predetermined.

Kansas, which is also a very conservative state, resoundingly rejected a ballot measure in August that would have stripped abortion rights from its state constitution.

Michigan

In Michigan, voters will decide whether to amend the state constitution to protect not just abortion but reproductive rights broadly.

This includes abortion, contraception, prenatal care, postpartum care, miscarriage management, sterilization and infertility. The state would be able to regulate abortion after the fetus is viable, but not prohibit the procedure when the woman's life or physical or mental health is at stake.

The campaign to protect reproductive rights under the state constitution comes after a legal battle in Michigan last summer over a 91-year-old abortion ban. The Supreme Court's decision to overturn Roe raised the possibility that the ban from 1931 could go back into effect in Michigan.

The old law was blocked and subsequently struck down by a state judge who ruled that it denied women control of their bodies and their lives. The midterm ballot measure would prevent any future legislature from banning abortion. Some 64% of Michiganders support the constitutional amendment, according to a poll from the Detroit Free Press.

Abortion rights activists have spent more than $28 million through the political action committee Reproductive Freedom for All to support the constitutional amendment, according to Michigan campaign filings. Those who oppose it have spent more than $16 million through another PAC, Citizens to Support MI Women and Children.

Michigan is poised to become a crucial access point for women seeking abortions from neighboring Midwestern states. Indiana passed a law in August that almost totally bans abortion. Ohio banned the procedure after fetal cardiac activity is detected, which is often around the sixth week. The Indiana and Ohio laws are both currently blocked by courts pending state constitutional challenges.

Women in Kentucky, where a ban is currently in effect, are also within driving distance of Michigan.

California and Vermont

California and Vermont are also voting during the midterms on whether to protect abortion under their state constitutions.

The California constitutional amendment would prohibit the state from denying or interfering with a woman's freedom to have an abortion or use contraception. Nearly 70% of voters in the Golden State support the amendment, according to the Public Policy Institute of California.

The Vermont amendment would guarantee an individual's right to personal reproductive autonomy. Some 75% of voters in the Green Mountain State support the amendment, according to an October poll from the University of New Hampshire.

Abortion was never in jeopardy in these very liberal states even after Roe fell. Nash, at the Guttmacher Institute, said the state constitutional amendments guarantee the procedure will be available to future generations if the political winds change.