Rare Case of a Woman Giving Birth to Twins Conceived Simultaneously by Two Different Men

In 2018, a woman came to the Laboratory of Population Genetics at the National University of Colombia seeking to identify the fathers of her two-year-old twins. This laboratory routinely conducts paternity tests, which were performed twice in this case to ensure accuracy. The results were astonishing: although the twins were born to the same mother, each twin had a different father. This extremely rare phenomenon is known as “heteropaternal superfecundation.” According to scientific records worldwide, only 20 such cases have been documented so far. While the experts at the Colombian university had theoretical knowledge of this possibility, they had never witnessed it firsthand. Upon confirming this occurrence in their own lab, the scientists expressed increased interest in studying it further.

For the paternity testing, the lab employs a technique called “microsatellite marker” analysis. Simply put, this method involves examining and comparing small DNA segments collected from the child, mother, and potential fathers. “We analyze between 15 to 22 microsatellite loci in each individual’s DNA and compare them one by one,” explained Professor William Usaken, the test director. The process is complex: after collecting a blood sample via finger prick, scientists isolate small amounts of DNA by removing other components through chemical treatment. The DNA is then amplified using specialized equipment. A fluorescent dye is added to the resulting solution, highlighting the microsatellite regions that need to be analyzed.

In the case of the Colombian twins, the scientists compared 17 microsatellite loci from the twins, their mother, and the tested individuals. The results showed that one twin’s DNA matched with one man’s DNA, while the other twin’s DNA matched with a different man. This was an exceptionally unusual finding. “I have been the director of this laboratory for 26 years, and this is the first and only such case we have ever observed,” said Usaken.