When she was told it could be two years before a donor agreed to his sperm being used by a single woman, she advertised.
"When you get to my age you might only have a year or two when you can have more children, so I could be out there in the dating scene and trying to meet men and all of that is just so unstable for my little son.
"And even if I met the perfect man tomorrow it's going to take a year or two to get to know each other, decide you want to have a child, and then it's almost too late biologically."
The woman, who would also foot the $1500 bill for the donor insemination cycle, said many single women made dedicated mothers.
Karen described herself as a well-educated professional who was able to provide a stable, happy home for another child and had support from her family.
She did not want to ask friends to be sperm donors because "that's a really awkward conversation to have", but she hoped the donor would eventually be known to the child.
So far she had received eight genuine responses through Repromed Auckland, a private fertility clinic, though it is expected not all of them will be able or want to continue the process.
Repromed clinical director Dr Guy Gudex said finding donors in New Zealand, where it is unpaid, had always been difficult and demand for them had increased.
"But it's got even harder over the past 10 or 15 years. One of the reasons is the whole identifiability issue.
"That requirement that you one day might be identifiable might put some people off."
Dr Gudex said a significant amount of sperm donation is for same-sex couples and single women.
"There's just an increasing number of women who either by choice or by circumstance don't have a partner and are getting concerned about age.
"A lot of them approach us in their mid to late 30s and the dilemma with that is donor insemination works best in women under the age of 40."
He said there was at least a 12-month wait and in some cases longer.
Donors can specify who gets their sperm, for example, they may exclude single mothers.
Process for NZ donors
• Sperm donation is not commercialised in New Zealand, making it illegal to pay a sperm donor. And a child conceived through donation has the right to identifying details at 18.
• The process for a donor involves a comprehensive health questionnaire, blood screening for HIV, hepatitis and genetic disorders, counselling including with the donor's partner, banking the sperm over several months, and a final round of blood screening.
• The donor can withdraw consent right up until fertilisation with an egg or insemination.
• The aim is to make up to five families from one donor.
• Donors can be between 18 and 50 but preferably younger than 45, when sperm quality declines.
