Sperm donation
Sperm donation is the practice by which a man donates his semen for the express purpose of it being used to produce a baby. A man who donates sperm, a sperm donor, may do so at a clinic known as a sperm bank.
Sperm donation commonly assists couples unable to produce children because of 'male factor' fertility problems, but it is increasingly used as a means to enable single women and lesbian couples to have their own children.
Donors may be either anonymous or non-anonymous, although laws may require donors to be one or the other, or restrict the number of children each donor may father. Although many donors choose to remain anonymous, new technologies such as the internet and DNA technology has opened up new avenues for those wishing to know more about the biological father, children or half-siblings.

# Types of donors

## General
Many sperm donors donate their sperm for purely altruistic reasons so that childless women or couples may produce their own children. Where such donations are through a sperm bank, the sperm bank will generally re-imburse the donor his reasonable expenses.
Some sperm donors may however, seek financial compensation, particularly those who supply sperm samples to order at specific times and at a specific sperm bank on a regular basis for what may be many months, in the knowledge that these samples will be used to produce a number of pregnancies. Many sperm banks therefore offer financial rewards which more adequately compensate for such a commitment. A sperm donor will rarely, if ever, know the exact number of pregnancies which his samples have produced, and indeed, an accurate or exact figure very often will not exist.
In the past sperm banks were keen to recruit as sperm donors men who had already fathered children. However, with the advances of microbiology, sperm can readily be checked for its fecundity, and sperm banks will now rely upon their own tests to ensure the quality of sperm.
Sperm donors are required to be fit and healthy and generally their 'sperm count' will be well above average to ensure that pregnancies may be easily and swiftly achieved by the use of their sperm.

## Anonymous or non-anonymous

### Anonymous
Most sperm donors are anonymous, i.e. the clinic will never give contact information of the receiving woman/couple and the woman/couple will not be told the identity of the donor. However some information about the donor may be released to the woman/couple. A limited donor information at most includes height, weight, eye, skin and hair colour. In Sweden, this is all information a receiver gets. In the US, on the other hand, additional information may be given, such as a comprehensive biography and sound/video samples.
The law usually protects sperm donors from being responsible for children produced from their donations, and the law also usually provides that sperm donors have no rights over the children which they produce.

### Non-anonymous
Several countries, e.g. Sweden, Norway, the Netherlands, Britain, Switzerland, Australia and New Zealand only allow non-anonymous sperm donation. The child may, when grown up (15-18 years old), get contact information from the sperm bank about his/her biological father. In Denmark, a sperm donor may choose to be either anonymous or non-anonymous. Nevertheless, the initial information which the receiving woman/couple will receive is the same.

## Private donors
Besides the men who donate to a sperm bank there are also less institutional donations, for example, a would be mother may approach a friend, or may obtain a "private" donor by advertising.  A number of web sites seek to link such donors and donees, while advertisements in same sex publications are not uncommon.  Although artificial insemination is usually used, frozen sperm need not be.  Most such donors meet the donees and are therefore usually known to the recipient.  Private donations are usually free - avoiding the significant costs of a more medicalised insemination - and theoretically, where fresh rather than frozen semen is used the chances of pregnancy may be higher.  Against this are the usually higher risks of disease transmission and the risk of a legal dispute regarding access or maintenance.  The laws of some nations (e.g. New Zealand), allow for recognition of written agreements between donors and donees in a similar way to institutional donations. In others, e.g. Sweden, this is not guaranteed.

# Limitation
Where a sperm donor donates sperm through a sperm bank, the sperm bank will generally undertake a number of medical and other checks to ensure that the donor's sperm are fertile and motile, that the donor's sperm will withstand the freezing and thawing process necessary to store and quarantine the sperm, and that the donor is healthy and will not pass on any diseases through the use of his sperm. The cost to the sperm bank for such tests is not inconsiderable. This normally means that clinics may use the same donor to produce a number of pregnancies in a number of different women.
The number of children permitted to be born from a single donor varies according to law and practice. Laws vary from state to state, and a sperm bank may also impose its own limits. The latter will be based on the reports of pregnancies which the sperm bank receives, although this relies upon the accuracy of the returns and the actual number of pregnancies may therefore be somewhat higher. Nevertheless, sperm banks frequently impose a lower limit on geographical numbers than some US states, although they may not, in practice, limit the overall number of pregnancies which are permitted from a single donor world wide. When calculating the numbers of children born from each donor, the number of siblings produced in any 'family' as a result of sperm donation from the same donor are almost always excluded (but see below for the provisions in various states).
Where a limit on the number of offspring which are allowed to be produced from each donor is imposed, this is usually in order to reduce the chance of consanguinity by the half-siblings of the donor. Nevertheless, some donors may produce substantial numbers of offspring, particularly where they donate through different clinics, where sperm is exported to different jurisdictions, and where countries or states do not have a central register of donors.
A sperm donor generally enters into an agreement with the sperm bank to supply sperm usually once a week for a period of between six months and two years, depending on the extent to which the sperm bank may be able use the samples donated. Some sperm banks impose a maximum length for the period of donation (usually not more than two years) specifically so that this acts as a limit on the overall number of samples which it will have available from a single donor.
A single donation prepared for ICI or IUI use will usually produce at least one pregnancy, while samples prepared for other ART use may fertilise up to eight batches of eggs. The success rate for embryos subsequently implanted in a woman is approximately between 20 and 45% (see assisted reproduction).
Sperm banks frequently publish their 'pregnancy rates' which are success rates according to the number of pregnancies achieved as a percentage of the total number of treatments provided. These rates vary from clinic to clinic, according to the method of insemination used and of the ages of the recipients. Sperm from a sperm donor may be used by a clinic until the maximum number (if any) of live births in each case has been achieved.

## Australia
In Victoria, there is a limit of 10 families per donor.
In Western Australia, the Human Reproductive Technology Act 1991 (HRT Act) limits the number of families for each donor to 5.

## Belgium
The medical practitioner performing the procedure will set his or her own limit on the number of pregnancies from each donor which will depend upon the size of the community where the recipient is resident. This also applies to foreign women who are treated in Belgium.

## Denmark
In Denmark, one donor may give rise to 25 children. 
However, Denmark also exports semen to other countries, and for the donors participating in that way there is practically no limit. Since the limits for each country that is receiving the samples are followed, the risk of consanguinity is reduced.

## New Zealand
In New Zealand, a voluntary policy law by fertility clinics limit one donor to "fathering" a maximum of 10 children to 4 families.

## Spain
The medical practitioner performing the treatment will set his or her own limit of live births from one donor according to the size of the community where the donee is resident. This also applies when foreign women are treated in Spain.

## Sweden
In Sweden, a donor may give a child to a maximum of 6 couples. However, each pair may have a sibling in addition. Thus, the limit is 12 children per donor.   Nevertheless, the Swedish National Board of Health and Welfare (Socialstyrelsen) recommends a maximum of 6 children per donor.

## UK
The HFEA sets a limit of 10 families within the UK which can be created using the gametes of one donor. However, there is no limit to the number of children which may be born to each such family from the same donor. A donor may set a lower limit and may impose conditions on the use of his sperm. In addition, there is no prohibition on the export of sperm from the UK provided that the number of families created in the UK does not exceed ten at the time of the export. This means that in practice some donors may produce substantial numbers of children, particularly where sperm samples are exported within the European Union to countries such as Belgium or Spain. Special permission is required from the HFEA for the export of embryos.

## USA
In the USA, the ASRM guidelines limit a donor to 25 live births per population area of 850,000, although this is not enforced by law, there is no central tracking, and it has been estimated that only about 40% of births are reported.  It is likely that some donors have over one hundred genetic children.
Some sperm banks impose lower limits; e.g., the Sperm Bank of California has a limit of ten families per donor , and the Rainbow Flag Sperm Bank has a limit of donor children by six different women.

# Donor tracking
Even when the donor had chosen to be anonymous, there are still opportunities to find the biological father for curious people conceived by donor sperm. Registries and DNA-databases are useful for this purpose.

## Tracking by registries
The Donor Sibling Registry (www.donorsiblingregistry.com)is a registry to facilitate donor conceived people, sperm donors and egg donors to establish contact with genetic kindred. They are mostly used by donor conceived people to find genetic half-siblings from the same egg- or sperm donor.
Some donors are non-anonymous, but most are anonymous, i.e. the donor conceived person doesn't know the true identity of the donor. Still, he/she may get the donor number from the fertility clinic. If that donor had donated before, then other donor conceived people with the same donor number are thus genetic half-siblings. In short, donor sibling registries matches people who type in the same donor number.
Alternatively, if the donor number isn't available, then known donor characteristics, e.g. hair, eye and skin color may be used in matching siblings.
Donors may also register, and therefore, donor sibling registries may also match donors with their genetic children.

## Tracking by DNA-databases
However, even sperm donors who have not initiated contact through a registry are now increasingly being traced by their offspring. In the current era there can be no such thing as guaranteed anonymity. Through the advent of DNA testing and internet access to extensive databases of information, one sperm donor has recently been traced. In 2005 it was revealed (3-Nov-05 New Scientist Magazine) that an enterprising 15-year-old used information from a DNA test and the internet to identify and contact his genetic father, who was a sperm donor. This has brought into question the ability of sperm donors to stay anonymous.