London, March 2 (IANS): Many couples experience involuntary childlessness and seek treatment at fertility clinics and to improve outcomes for such couples, a significant study has revealed that the hotly debated egg stem cells do not exist in human overy.

Researchers at Karolinska Institutet in Sweden analysed all cell types in the human ovary to reach this conclusion.

The new study substantiates previously reported findings from animal studies - that egg stem cells do not exist.

Instead, these are so-called perivascular cells, said the study published in Nature Communications.

"The question is controversial since some research has reported that such cells do exist, while other studies indicate the opposite," said Lanner, researcher in obstetrics and gynaecology at the Department of Clinical Science, Intervention and Technology at Karolinska Institutet, and one of the study's authors.

The researchers used single-cell analysis to study more than 24,000 cells collected from ovarian cortex samples of 21 patients.

They also analysed cells collected from the ovarian medulla, allowing them to present a complete cell map of the human ovary.

One of the aims of the study was to establish the existence or non-existence of egg stem cells.

The question of whether egg stem cells exist affects issues related to fertility treatment, since stem cells have properties that differ from other cells.

"Involuntary childlessness and female fertility are huge fields of research," said co-author Pauliina Damdimopoulou, researcher in obstetrics and gynaecology at the same department.

"This has been a controversial issue involving the testing of experimental fertility treatments."

The new comprehensive map of ovarian cells can contribute to the development of improved methods of treating female infertility, the authors wrote.

"The lack of knowledge about what a normal ovary looks like has held back developments," said Damdimopoulou.

The results showed that the main cell types in the ovary are egg cells, granulosa cells, immune cells, endothelial cells, perivascular cells and stromal cells.

"This study now lays the ground on which to produce new methods that focus on the egg cells that already exist in the ovary. This could involve letting egg cells mature in test tubes or perhaps developing artificial ovaries in a lab," the authors wrote.