Kate Hill from Australia was undergoing fertility treatment in order to have children when she fell pregnant not once but twice.

The woman went down in medical history as there are only ten documented cases of this medical phenomenon called "superfetation" worldwide.

Kate was previously diagnosed with polycystic ovarian syndrome (PCOS) and received hormone treatment before becoming pregnant.

As she fell pregnant the second time while already being pregnant, doctors were baffled after seeing that she had twins.

Doctors found out later that Kate was actually pregnant with triplets but lost one during the first weeks of pregnancy.

Although the twins were given two different due dates, they were born together and named Charlotte and Olivia.

Today, the twins are 10months-old and are different in size, weight and even blood groups.

Photographer Selena Rollason who took the black and white photos of the babies also won Australia's best birth photographer of the year award.

Women who are diagnosed with polycystic ovaries usually have difficulty getting pregnant and have a high infertility rate. Some women with PCOS will ovulate, whereas others do not over ovulate, hence it usually requires treatment to improve chances for pregnancy.