More than half a million women still die every year in pregnancy or after childbirth in spite of two decades of efforts to bring down the toll, reports reveal today.

Little has changed, particularly in much of the developing world. Women die of avoidable complications such as high blood pressure or haemorrhage in childbirth - and often the baby dies too or does not survive the next few years without a mother. Tens of thousands die painfully in backstreet abortions in countries where contraception is not readily available and abortion is heavily restricted or banned.

Papers prepared for a major conference in London next week and published in the Lancet today reveal the scale of the failure. New figures show it is highly unlikely that the Millennium Development Goal 5 - to slash death rates by 75% from their 1990 level by 2015 - will be achieved.

In 1990 it was estimated that 576,300 women died in pregnancy, labour or after giving birth. The latest calculations, from the Harvard Centre for Population and Development Studies in Cambridge, Massachusetts, show that 15 years later, in 2005, some 535,900 died. The maternal mortality ratio dropped from 425 in 100,000 to 402 in 100,000.

But that, says Ken Hill, lead author of the paper, is a best estimate. Because of the lack of data from some of the countries with the worst death tolls, calculations have to be based on better performing countries that do collect figures. That makes it look as though there has been a drop of 2.5% in the mortality rate a year but it could be as low as 0.4%.

"0.4% unfortunately I think is the more realistic figure for the globe as a whole," said Professor Hill. "The proportion of sub-Saharan African births is going up and maternal mortality is not going down."

Abortion rates have dropped, mostly due to a big rise in contraceptive use in eastern Europe. Globally numbers came down from 46m in 1995 to about 42m in 2003. But the picture in Africa and parts of Asia remains dire and some experts accuse the Bush administration of worsening the problem due to its anti-contraception, pro-abstinence policies there.

"There couldn't be a better set of findings to show the failure of the Bush administration policy - the emphasis on abstinence and monogamy, the obsession with abortion, the defunding of good family planning organisations because they talk about abortion," said Sharon Camp, president and CEO of the Guttmacher Institute, which carried out the abortion study with the World Health Organisation.

"You'd think people who want to reduce abortion would stand up for family planning services, but as soon as you scratch the surface they have a much broader agenda. They are basically opposed to sex outside marriage in the more extreme cases," she said.

In Uganda, which she calls "the Bush administration showcase for monogamy in relation to HIV/Aids", the abortion rate is 54 for every 1,000 women aged 15-44, whereas in the US it is 21 for every 1,000.

Ann Starrs, executive vice-president of Family Care International in New York, one of the organisers of the Women Deliver conference in London next week, said the key message would be that "investing in women's health and wellbeing is fundamental to the economic development of families, communities and nations".

The loss of a woman in childbirth was the loss of a breadwinner and had serious consequences for a family. Nine times out of 10 the baby would die with her or within the next few years. Older children were less likely to be educated and more likely to be malnourished or sick. She estimated the cost of the loss to women's productivity at $15bn (£7.3bn) a year.

Several UN agencies are involved in the conference. "In this 21st century no woman should die giving life," said Thoraya Ahmed Obaid, executive director of the UN Population Fund. "It is unacceptable that one woman dies every minute during pregnancy and childbirth when proven interventions exist. Millions of lives are at stake, and we must act now."

Several interventions are proven to cut deaths, she says in an editorial in the Lancet. They include access to voluntary family planning, which could reduce women's and infant deaths by a third. Ensuring skilled attendance at all births and having emergency obstetric care available could reduce the death rate by about 75%.