After he talked about his family’s fertility struggles on the campaign trail, Democratic vice presidential nominee Tim Walz is facing criticism from his opponent for not accurately having identified the treatment his wife, Gwen, received.

The Republican vice presidential nominee, Sen. JD Vance, of Ohio, accused Walz on Tuesday of lying about having conceived his children via in vitro fertilization. Vance seemed to be responding to an article in Glamour magazine, in which Gwen Walz said she had undergone a fertility treatment called intrauterine insemination.

“It’s just such a bizarre thing to lie about, right? There’s nothing wrong with having a baby through IVF or not having a baby through IVF. Like, why lie about it? I just don’t understand that,” Vance told reporters in Milwaukee.

“Anybody who’s had a friend or themselves on fertility treatment, you know the difference,” he added.

Both IVF and IUI are forms of assisted reproductive technology. IVF involves retrieving eggs from the ovaries and fertilizing them with sperm in a laboratory, then transferring one or more embryos into the uterus. IUI involves putting sperm directly into the uterus. Either way, a doctor inserts a small, flexible tube into the vagina to place the sperm or an embryo into the uterus.

Some staunch abortion opponents are against the practice of discarding embryos, a common part of the IVF process. Like most Republicans, Vance has voted against Democratic legislation to protect IVF.

Tim Walz has never directly said he and his wife had their children via IVF, but some of his past statements have implied that was the case.

In February, after the Alabama Supreme Court ruled that embryos created through IVF were considered children (meaning people theoretically could be sued for destroying them), Walz wrote on Facebook that he and his wife “have two beautiful children because of reproductive health care like IVF.”

And last month, he said on the “Pod Save America” podcast that, if it were up to Vance, “I wouldn’t have a family because of IVF and the things that we need to do reproductive. My kids were born through that direct — you know, that way.” 

Mia Ehrenberg, a spokesperson for the Harris-Walz campaign, said in a statement Tuesday that Walz “was using commonly understood shorthand for fertility treatments” in his previous comments.

“The Trump campaign’s attacks on Mrs. Walz are just another example of how cruel and out of touch Donald Trump and JD Vance are when it comes to women’s healthcare,” Ehrenberg said.

Several fertility doctors said it’s common to conflate IUI and IVF.

“Whenever someone thinks they’re doing fertility treatments, they think automatically they’re doing IVF,” said Dr. Brian Levine, founding partner of CCRM Fertility New York.

In reality, he added, “there’s gradations of treatment, and IUI is one of the tools that’s in my toolbox.”

Dr. Eli Reshef, an infertility specialist at the Advanced Fertility Center of Chicago and an advisory board member at WINFertility, said “the majority of my patients, not all, know the difference” between IUI and IVF.

There can be overlap between the two processes. For instance, Gwen Waltz said in a statement Tuesday that her treatment involved injections, which are typically the shots IVF patients use.

“The only person who knew in detail what we were going through was our next door neighbor. She was a nurse and helped me with the shots I needed as part of the IUI process,” she said. “I’d rush home from school and she would give me the shots to ensure we stayed on track.” 

In most cases, patients undergoing IUI take pills to stimulate the production of eggs, but a minority use injectable hormones. In that sense, medications most commonly associated with IVF have played a role in some couples’ success with IUI.

Injections may be used in the IUI process for a few reasons, said Dr. Shaun Williams, a partner in reproductive endocrinology at Illume Fertility in Connecticut.

“If we haven’t been successful with getting two or three eggs each month, then we’ll sometimes move to the more potent medication to try to have a higher likelihood of success,” Williams said.

He added that some people also opt for injections because they “are limited by the number of attempts that they can do, based on either insurance coverage limitations or cost.”

IUI has a lower success rate per cycle than IVF, but it’s less expensive and invasive. People undergoing IVF must give themselves shots daily for one to two weeks and get frequent ultrasounds and blood draws. The egg retrieval procedure requires anesthesia and involves inserting a needle into the ovaries to remove the eggs.

Many fertility specialists suggest trying IUI first. Some patients also aren’t candidates for IVF.

“I tell my patients: ‘Let’s do three IUIs. If that’s not successful, let’s talk about the more involved and expensive cousin: in vitro,’” Reshef said.

Both IVF and IUI are often highly stressful and emotional for couples hoping to conceive.

“When my wife and I decided to have children, we spent years going through infertility treatments,” Walz said this month at a rally in Philadelphia. “And I remember praying every night for a call for good news, the pit in my stomach when the phone rang and the agony when we heard that the treatments hadn’t worked. So it wasn’t by chance that when we welcomed our daughter into the world, we named her Hope.”