And then there was one

Abstract

WHILE you were quietly growing, waiting to be born, was someone there beside you? Tucked up alongside may have been a twin brother or sister, whose ghostly form disappeared long before your mother even felt you kicking. At least 1 in 20 of us is in fact a twinless twin. Do the maths, and the statistics for these vanishing twins seem shocking - of the estimated 133 million people born in the world last year, at least 7 million should have had a twin. For parents who learn that one twin of a pair perished early in pregnancy, the news can be heartbreaking. They need answers. What happened? Viewed in the cold light of biology, such losses are sadly unsurprising. As any woman who has suffered an early miscarriage knows, human reproduction is brutally inefficient. About three quarters of all conceptions never make it to term, most being lost in the first few weeks of pregnancy. And a twin may appear on an early ultrasound only to disappear by the next. "Losing one or both offspring is too common to be called phenomenal, and occurs for too many different reasons to qualify as a syndrome," says Charles Bocklage, a developmental biologist at East Carolina University in Greenville, North Carolina. For women who lose a twin, the knowledge that the process is a natural one may help ease the feelings of guilt they often suffer. But vanishing twins are more than just a grim example of nature's wastefulness. They may also help us to understand some of the causes of many infant disabilities such as heart defects and cerebral palsy.