The woman, Kate Hill was receiving hormone treatment for polycystic ovary syndrome, a condition which meant she was not ovulating. She apparently conceived the twins at different times despite only having unprotected sex once. Medical experts believe her fertilized egg split into two, a rare phenomenon known as Superfetation.
The twin girls, Charlotte and Olivia Hill, were born 10 months ago with different sizes, weights and gestational development, according to reports. There are only ten cases of Superfetation documented across the world. The couple’s obstetrician, Dr Brad Armstrong said the condition was so rare he was forced to search for it online. “I could not find any literature in the medical review websites at all,” he said.
Pregnancy normally stops the monthly cycle of ovulation but very rarely a woman can release another egg after conceiving. If this is fertilised it could also implant and develop into a healthy pregnancy.
“Normally with twins, both eggs are released at the same time and conceived at the same time. But in this case, one egg appears to have been released 10 days later and the sperm survived in the female genital tract before fertilising the other egg. We do know that sperm can survive in the female genital tract for up to a week, but usually not for 10 days.” Professor Michael Permezel, the president of the Royal Australian and New Zealand College of Obstetricians and Gynecologists said.