Adoptive parents are welcoming a call to rewrite New Zealand's 54-year-old adoption law - but say the most urgent need is to legislate for "open" adoptions where birth parents can keep in touch with their children.

Acting Principal Family Court Judge Paul von Dadelszen called this week for a review of the 1955 Adoption Act to remove discrimination against de facto and gay couples, who are currently barred from adopting.

But groups representing the country's dwindling numbers of adoptive parents said adoption was now so rare that they had had inquiries from only a handful of de facto and gay couples wanting to adopt.

Simon Kingham of the Adoption Option Trust in Christchurch said the biggest problem with the law was that it was written at a time when adoptions were "closed", meaning birth parents gave up all contact with their children.

Today virtually all adoptions are "open" and birth parents actually choose the adoptive parents for their babies - and stay in touch.

Dr Kingham and his wife, Sue, have an adopted girl aged 6 and a boy aged 4. Both children see not just each of their respective birth parents but also their birth grandparents, aunts, uncles and cousins.

"So in terms of grandparents they have six lots of grandparents," Mrs Kingham said.

"For me, being brought up in an open adoption is no different from a blended family, you just have more people in your life to love you."

Not all adoptions are quite so open. Mrs Kingham said some birth parents still wanted to keep their babies secret and just occasionally receive photos.

But Dr Kingham said Child, Youth and Family's adoption service encouraged open adoptions and New Zealand led the world with them.

The only problem was that, because the law had not kept up with changed practice, birth parents had no legal rights to maintain contact with their children if the adoptive parents later tried to exclude them.

"The law needs to change to give biological parents some legal protection against people changing their minds," he said.

Adoptions have declined dramatically since 1955 as both solo parenting and abortion have become more socially acceptable.

Adoptions outside the birth parents' family rose from about 1000 a year in the mid-1950s to a peak of 2617 in 1968, but have plunged to fewer than 100 a year in most recent years. There were just 77 last year.

A group of Christchurch birth mothers are about to launch their own Birth Mums Support Network to support young mothers wanting to explore open adoption.

Michele Daly of the Auckland-based Open Adoption Network, a social support group for adoptive parents, said she had only 150 couples on her database nationally, 80 per cent of them in Auckland.

She said the group included at least one couple who married so that they could adopt, because of the Adoption Act's rule that only married couples or individuals can adopt.

The network also includes same-sex couples where one partner has adopted but the couples cannot adopt children together.

"My personal view is that the law needs to be changed so that it's a reflection of the society that we have today," she said.

But Catholic bishops yesterday expressed concern that the debate about the law was focusing on the rights of adults, with almost no reference to the rights of children.

Bishop Peter Cullinane of Palmerston North said the church wanted to protect the rights of children.

"We accept the view, held by many researchers, that a mother's and a father's love are different and complementary, and that a child has a right to both."