The XO Directory

Ame and Lia are not twins but the two are born on the same day (just minutes apart) to the same mother, 29-year-old Miss Spence. The five-month-old babies look like twins, but in fact they're not. They were conceived three weeks apart - a million-to-one medical rarity.

An explanation for this unusual case:The girls were conceived through a process known as superfetation, the term used to describe the formation of a foetus whilst another foetus is already present in the uterus.

This occurs when eggs from two separate menstrual cycles are released, as opposed to normal non-identical twins where more than one egg is released in a single cycle. Although common in animals it is rare in humans, but it can result in a twin or multiple pregnancy. It is diagnosed when the foetuses show a marked different in development. The girls are technically not twins. Identical twins occur when one egg splits into two and non-identical, or fraternal, twins occur when two eggs are released and fertilised at the same time.

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