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When Women Fail Maternity Tests: The Fascinating World of Natural Chimerism
Several years ago a woman named Lydia Fairchild applied for welfare. She was pregnant and had two children. They forced her to take a DNA test…which showed that she was not the mother of her own children. The children she carried and gave birth to. Fairchild was accused of welfare fraud and illegal surrogacy. Social services threatened to take the children. Her third child’s birth was witnessed, but again, tests showed she wasn’t the mother. She was accused of carrying somebody else’s baby.
There have been a handful of cases of failed maternity tests (and at least one failed paternity tests) that happened because the parent was a chimera. Specifically, a tetragametic chimera. In some cases, fraternal twins are conceived, but they merge together, kind of the reverse of the splitting process that creates identical twins. This results in one person with two sets of DNA. When the gonads are created from a different cell line from the skin, a swab test will show a mismatch between the child and the parent. This is very rare, but may be more common than we think. And yes, it’s possible for somebody to have two cell lines that carry different sex chromosomes. Another variant is twin chimerism, where one twin dies and the other absorbs a few cells, resulting in occasional parts of the body from the other cell line.