About 150 women have frozen their eggs for non-medical reasons at a Melbourne IVF clinic over the past 15 years - but only 15 women have returned to use them. The low return rate has prompted researchers to study their cases to help inform other women contemplating egg storage. Melbourne IVF director John McBain said egg freezing had long been an option for women wanting to preserve their fertility ahead of cancer treatment, but was now becoming more common for ‘‘social reasons’’ - particularly single women concerned they may not meet a partner until later in life. Associate Professor McBain said a new study would invite women who had frozen their eggs at Melbourne IVF for social reasons to share their experiences, including what led them to store eggs and why they may not have gone on to use them. He said the study, being conducted by Melbourne IVF in partnership with Monash University’s Jean Hailes research unit and Melbourne University’s department of obstetrics and gynaecology, was important amid growing interest in egg freezing for social reasons. The procedure costs about $10,000. With few women returning to use frozen eggs, Associate Professor McBain said it was important ''‘to know what happened to the others so we can better inform people considering that option now''. Associate Professor McBain said of the 15 women who returned to use their frozen eggs, five went on to have successful pregnancies. But he said a new freezing technique called vitrification had greatly improved the chance of eggs surviving the freezing and thawing process in recent years, making successful fertilisation through IVF more likely. ''A woman would once have needed to freeze about 40 eggs to have a good chance of having a child, but that is now down to about 10 eggs,'' he said. Associate Professor McBain said women would ideally freeze their eggs by the age of about 32, after which fertility began to decline. But he said many women contemplating egg freezing for social reasons were in their mid-30s or older and he warned that advancing age could have a negative impact on the number and quality of available eggs. ''The reality is that while the success of egg freezing has improved significantly over the past 20 years, egg freezing still only offers a finite number of opportunities to have a successful pregnancy in the future,'' he said. A Melbourne mother who wanted to remain anonymous said she was single and still looking for the right partner when she chose to freeze eggs aged 38. She had a fresh IVF cycle at 42 after deciding to go ahead and have a child, but found she had no viable eggs left. ''I ended up having to use my frozen eggs and now I have an 18-month-old incredible child who has changed my life. [Freezing my eggs] was the best decision I’ve ever made,'' she said.