Tagg Romney and his wife, Jen, announced the birth of twin boys in May with the help of a surrogate mother and in vitro fertilization — a form of assisted reproductive technology that could be rendered illegal under the Sanctity of Human Life Act, co-sponsored by Ryan.
The bill states that human life begins the moment an egg is fertilized. But in IVF, some embryos are typically destroyed or discarded in the process after being fertilized by sperm outside the body.
Typically, doctors fertilize several eggs; the ones that fail to thrive after being implanted in the womb are discarded. Leftover embryos that are not implanted are often frozen, used for medical research or destroyed.
Many right-to-life groups oppose IVF since it results in the destruction of human embryos.
Women's groups have been zeroing in on Ryan's anti-abortion record ever since he was unveiled as Romney's running mate over the weekend.
They point out that Ryan, a Catholic congressman from Wisconsin, has consistently earned a 100 per cent voting approval rating from the National Right to Life Committee.
Romney, meantime, has a famously erratic record on abortion, stem cell research and even IVF.
The former Massachusetts governor attempted to explain away his wildly divergent public comments on IVF embryos as recently as May, when he was asked in an interview about his new twin grandsons.
"I believe that when a couple gets together and decides that they want to bring a child into the Earth, and they go to a fertility clinic to do so, and if they're going to be through that process a leftover embryo or two, that they should be able to decide whether to preserve that embryo for future use or to destroy it," he said, adding that those embryos can be utilized for "research and experimentation."
"And so for me, that's where the line is drawn. Those surplus embryos from fertility clinics can be used for research."
Yet Romney has also said he had an "epiphany" in 2004, becoming pro-life during a discussion with an embryonic stem cell researcher. A year later, however, Romney said he supported stem cell research using IVF embryos.
Ryan, on the other hand, has been steady in his belief that human life begins at fertilization throughout his seven terms as congressman. And in addition to co-sponsoring the Sanctity of Human Life Act and Right to Life Act, which both state life begins at fertilization, he also co-sponsored a law that prohibits federal funds from being used for any health-care coverage that includes abortion.
In a presidential election in which Democrats are attempting to portray Republicans as anti-women, Ryan's and Romney's apparently opposing viewpoints on IVF could cause headaches for them on the campaign trail.
"If Romney's sons have done something that the vice-presidential candidate thinks should be criminal, then that absolutely should and will become a campaign issue," Jo Freeman, a feminist writer and political scientist, said in an interview Tuesday.
"It's clear he approved of his son's actions, and now he has a running mate who would criminalize those actions. That's a problem."
As many as 60,000 babies are born in the U.S. every year thanks to IVF. A book written by Ron Scott, a distant cousin of the Republican presidential hopeful, claims that three of Romney's five sons have used the procedure to produce some of his 18 grandchildren.
"Three of the sons have wrestled with fertility issues in their own families and, to help things along, have sought solutions that are seemingly inconsistent with their father's views on abortion and stem cell research," Scott wrote in "Mitt Romney: An Inside Look At The Man And His Politics."
Romney and his children are practising Mormons. The Church of Jesus Christ of Latter-day Saints "strongly discourages" both surrogate mothers and IVF.
In messages on Facebook and Twitter in May, Tagg Romney made a point of thanking the surrogate after his twin boys were born. It was the second time he and his wife had used the surrogate; she also carried their two-year-old son, Jonathan.
"A special thanks to our gestational surrogate who made this possible for us," he wrote on Facebook. "Life truly is a miracle, and we feel so blessed to be able to celebrate the arrival of these precious boys into our family."
Romney's famously spotty record on abortion rights has caused the Republican party's Christian evangelical base to view him with deep suspicion.
While running for governor of left-leaning Massachusetts just 10 years ago, Romney pledged "to protect a woman's right to choose." He also frequently cited his brother-in-law's sister, Ann Keenan, an unmarried teen who died getting a botched illegal abortion in 1963.
Romney's own mother, Lenore, also unsuccessfully ran for the U.S. Senate in 1970 as an abortion moderate.
Freeman says Romney's veering positions are sadly typical of those seeking public office in the U.S.
"There's a strata of politicians in the United States for whom it is very important to be at the head of the parade," Freeman said.
"They don't care which direction the parade is going, so long as they're at the front. That's Romney, and that's why you see him flip-flopping on so many issues. He completely contradicts himself because he's seeking to appeal to whatever constituency he needs at the time, regardless of his personal beliefs."