Fertility options for women have never been greater but one vital ingredient is in short supply - sperm donors.
This means women hoping to conceive with the help of a fertility clinic will have to wait longer and have less choice about who their donor is.
Director Richard Fisher said the number of potential donors had dropped to less than a fifth of those in the late 1980s when there were about 65 men on the books.
Fertility Associates had 40 women waiting for a sperm donation at its Auckland and Hamilton clinics. It had enough sperm to treat 29 of them in the next six months. It was likely anyone registering with the clinic would have to wait at least 12 months.
Dr Fisher said the clinic had changed the profile of the men it accepted.
"Fifteen years ago we felt comfortable with younger men with good sperm counts, who may have been single. We have now changed our view. Donation of sperm is not just a physical issue, it's a social issue, particularly once we made a commitment that donors would be identifiable."
Men aged between 25 and 45, who already had families, were mature, recognised the value of having children and the importance of children having access to their genetic information were preferred donors.
They could give donations to up to three families, Dr Fisher said.
A potential donor must have sperm that is biologically sound and withstands freezing and thawing.
Recipient couples are offered donor profiles to choose from, which include information about the donor's background and medical history. Most people are offered no more than two choices.