The goal was to get to 24 weeks when the babies would be viable outside the womb, but they held on for an additional month and were delivered in September 2009.
At first their developmental milestones were a bit delayed, but now they are "well adjusted and caught up," according to their mother.
Although the Cunninghams pay little attention to the skin color of their babies, the world is not color blind.
Before they were married, the couple's co-workers had difficulty accepting their biracial relationship. They were ultimately fired from that auto plant where there were "huge racial overtones." Charles was reinstated only after the Ohio Civil Rights Commission investigated.
Later, neighbors in the rural community where they lived called Khristi Cunningham "the little white girl Charles had married."
When the story of their black and white twins was told on the blog, Mixed and Happy, some readers reacted negatively.
"They asked if we'd had genetic tests done," said Cunningham. Another remarked, "How can you do this to your kids?"
"No one gets to say if they are black or white," said Cunningham. "It's not a choice and to me they are perfect and will grow up to be loved.There's too much hate. People should be more worried about whether you're a Republican or a Democrat."
Last year, the same blog first reported a story about middle school in Nettleton, Miss., that restricted who could run for class office by race. The policy was a holdover from late 1960s desegregation orders.
Brandy Springer's daughter, a sixth grader of mixed white and Native American heritage, said her 12-year-old girl came home distraught because she would not be allowed to run for reporter, a position slated only for black students.
Springer also had another son of mixed white and Native American heritage and two younger children, who are mixed white and African American.
After a story ran on ABCNews.com and repeated calls to the school board and administrators, Superintendent Russell Taylor issued a statement revoking the policy that reserved class officers for specific races.
Incidents like these are not uncommon, even today when one in seven marriages is between spouses of different races, according to the Pew Research Center.
And for the first time, the 2010 Census allowed Americans to check more than one box to describe their ethnicity, results that are expected in March.
According to a recent report in The New York Times, the current group of college students is the largest group of mixed-race ever in the United States, fueled by immigration and intermarriage, and their numbers are expected to rise.
The editor for Mixed and Happy, Suzy Richardson, is white, married to a black firefighter and lives in Gainesville, Fla. The couple has four children aged 2, 4, 9 and 12.
"My oldest son has green eyes. Two of my children are dark and two are light," said Richardson, 34 and a former magazine editor.
Richardson grew up with a black stepfather and biracial sister who was "condemned by both sides -- black and white people."
When she met her African-American husband, she said, "I remember a black girl saying to me I would never date someone of another color."
Pregnant with their first child, she and her African-American husband were even denied seating in a small-town Florida diner.