Non-identical twins, Grace and Lana Jennings, are believed to have been conceived at different times, in a rare phenomenon called superfetation. Superfetation is where a foetus begins to grow in the womb when another developing foetus is already there.
Doctors think two eggs from two different menstrual cycles were released and that the girls grew at different rates in the womb. Twins usually occur when one egg splits or when two eggs from the same menstrual cycle are fertilised.
Mum Alison Jennings, 39, from Essex, and husband Stephen realised their twins were special when they had their 12-week scan. Grace was too small for the sonographer to do the scan.
Grace was born first, weighing 2.4kg, and sister Lana came next, weighing 3kg. The twins are now 5 months old, and mum Alison has said: “The girls are doing wonderfully. Grace is very laid back while Lana is a bit of a prima donna and wants to be number one.”
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