An estimated 114 million acts of sexual intercourse take place in the world every day.

Some 910,000 lead to conception and in 356,000 cases, a sexually transmitted disease is passed on, says the International Planned Parenthood Federation (IPPF).

The result can be pregnancy, infertility and, in the case of HIV, death.

Many of those affected are teenagers and adolescent sexual health is likely to emerge as one of the most contentious issues at the United Nations population conference in New York.

A spokeswoman for the UN Population Fund (UNFPA) said: "It is very contentious. Everyone is concerned because we have never had so many adolescents on the planet.

"Proponents of family planning say if we do not do something about it, there will be a huge problem.

"Even if adolescent couples only have two children, which is unlikely, the world's population will double in the next 50 years.

"But opponents say it is the beginning of a slippery slope."

A UN conference in Cairo five years ago agreed measures to tackle population growth, and basic education on reproduction issues was agreed to be a priority.

Click here to see UN Population Fund (UNFPA) figures on the impact of funding shortfalls.

The issue of family planning could also have a big impact on migration since 99% of the world's current one billion adolescents, aged 15 to 24, live in developing countries.

Church 'lobbying hard'

The crux of the problem centres around attitudes to sex education, contraception and the concept of individual reproductive rights.

The Catholic Church is said to have been lobbying hard against increased access to contraception. It believes it is immoral to prevent human life.

Pro-family groups believe sex education increases teenage pregnancy rather than the reverse.

Ann Widdecombe, former shadow health secretary in the UK, which has the highest levels of teen pregnancy in western Europe, recently stated: "There has never been so much sex education, free advice and contraception and yet we have record levels of teenage pregnancies".

However, family planning groups say sex education has been shown the world over to reduce pregnancy and accuse opponents are adopting a 'head in the sand' approach.

Dr Pramilla Senanayake, assistant secretary general of the IPPF, told a panel discussion on adolescent health: "To perceive young people as sexual beings still seems to be one of the hardest things to accept in most societies."

The issue of individual rights and sexual health is also highly political.

Family planning groups say reproductive health is the same as any other form of health and should therefore be a right of everyone.

But some countries, particularly in the developing world, argue that the idea of individual rights is a Western one.

They say the good of the community, including its moral wellbeing, should come before that of the individual.

Statistics

• It is estimated that one in 10 births a year is to teenage mothers. The number is one in six in the least developed countries.
• Some 70% of teen pregnancies are thought to be unwanted.
• In addition, one in 20 teenagers a year become infected with a sexually transmitted disease, according to the IPPF.
• Other issues related to teenage sexual health include female circumcision. It is estimated that up to two million young women a year undergo female circumcision. The process, which is traditional in many parts of the world, can lead to death and infection.
• Health experts believe providing modern family planning services to men and women could substantially improve health. The UNFPA estimates 350 million couples worldwide do not have access to the services they need.

Cairo and the world picture

The Cairo declaration calls for all countries to make reproductive health services more accessible, including to adolescents.

It also emphasizes the need for sexual health programmes to target men.

The IPPF says many couples do not discuss family planning because men are perceived to be against it when this may not be the case.

Since Cairo, a number of countries have reviewed their procedures for promoting sexual health.

For example, South Africa's new constitution recognises that everyone has the right to reproductive heath care.

Many are tying sexual health to women's empowerment.

Sri Lanka has approved a Women's Charter which accepts women's right to control their reproductive lives.

And several countries have set up bodies to safeguard women's rights.

In China, home of the notorious one-child policy, the government has abandoned birth quotas in some regions in favour of the introduction of high quality modern family planning services.

This includes offering couples more choice of contraceptives, such as the Pill.

Presently, the most common methods are IUDs and sterilisation.

The programme is accompanied by educational projects and financial incentives aimed at increasing women's participation in the Chinese economy.

Aids has accelerated efforts to raise awareness about sexual health

Hao Linna, deputy director of the Department for International Co-operation in the Chinese government's Family Planning Commission, said: "When you combine these elements with a renewed effort to deliver quality reproductive health services to more people, offering them a wider choice of contraceptives and services, we are convinced that people will make rational choices."

Health experts say that, ironically, the emergence of Aids has had the positive effect of forcing many countries to talk more openly about sex.

Aids is now the number one killer in Africa and is in the top five most dangerous contagious diseases worldwide.

The threat of the disease has led to urgent attempts to improve access to contraception and sex education in many countries.