Perhaps the most pervasive, and unmerited, argument regarding cousin marriages is that the children born to such couples will have mental or physical disabilities, which become a burden on society in terms of tax dollars.

The question is: How risky is it really to have a child with your cousin? The answer is: Not nearly as risky as so many other factors for which there is no legislation!

The above graph represents what are called "multifactoral" disorders. These multifactoral disorders include a wide range of problems, and are often associated with low birth weight or premature birth. These problems can include stillbirth, SIDS, under-developed lungs and other vital organs, mental retardation or learning disabilities, anemia, and heart conditions.

This chart indicates the 3% background risk shared by all pregnant women, and comparative increases of risk for various groups.
The graph above illustrates various inherited types of conditions, as well as the background risk (which everybody has) and the increased risk for specific groups. In general, a child who inherits a recessive disorder inherits one defective gene from each parent. Examples of recessive diseases include Cystic Fibrosis, PKU, Tay Sachs and Sickle Cell.

Dominant and Gender- or X-linked disorders, on the other hand, are ones in which the defective gene is inherited from only one of the parents. Any parent who is a carrier has a 50% chance of passing the disease on to their children. Dominant gene disorders include Neurofibromatoses, Marfan Syndrome, and PKD. Some examples of X-linked disorders are Hemophilia and Fragile X Syndrome.

The conditions that are of most concern in cousin couples are recessive conditions, where one defective gene is inherited from each parent. First cousins have a 1.5 to 3% increased risk of having a child with birth defects that are inherited. However, some couples may share no recessive traits,  and would therefore have no increased risk.

First cousins, once removed have an increased risk of .75 to 1.5%, and second cousins have no higher risk than an unrelated couple. Double first cousins are rare, but have approximately twice the risk of other first cousin relationships. First cousins whose parents are identical twins are also rare, and have a significantly higher risk as well, having the same number of shared genes as half siblings.

An Issue Of Reproductive Rights

In the spring of 2000, some members of Maryland’s House of Representatives presented a bill to prohibit marriages between first cousins in their state. Although this is an infrequent occurrence in Maryland (counties reported a range of one to three incidents per year, mostly from non-residents) the sponsors of the bill believed that such marriages produced physically and mentally challenged children, thus placing an enormous burden on taxpayers’ money. They argued for the bill based on erroneous statistics, but failed to validate their information with evidence. The bill died in the senate, but the sponsors have expressed a desire to resubmit it in 2002.

In the spring of 2001, quite a different scenario took place in the state of New Hampshire. First cousin marriages had long been forbidden in that state, and at the request of one of her constituents, Delegate Anne Grassie presented a bill to overturn that law, and allow one inidual to marry the woman of his choice.

Do cousin couples who wish to bear children pose such a risk to society that there should be legislation preventing their right to pursue happiness?

More than four million women become pregnant in America each year, each with a 3% background risk of having a child with a birth defect. Out of those four million women, it is estimated that:

  • .1% (4,000) of those women are pregnant by a first cousin
As the charts above indicate, the health risk to unborn children of first cousins is very nominal, particularly when combined with such a low frequency of occurrence.
  • 1.1% (45,000) use cocaine
Cocaine use increases the odds of intrauterine growth retardation by 15%, and also significantly increase odds of premature or low birth weight babies and related health problems, stillbirths, and SIDS.
  • 2.9% (119,000) smoke marijuana
Marijuana use during pregnancy may reduce the size of the fetus and the birth weight, and related health problems. There is also a 10-fold increase in the risk of nonlymphoblastic leukemia in children whose mothers used marijuana before or during gestation. Marijuana may also increase the risk of chromosomal damage.
  • 18.8% (757,000) drink alcohol
Alcohol consumption during pregnancy increases the risk of birth defects by 9%. Additionally, one out of every 750 newborns are born with FAS (Fetal Alcohol Syndrome.)
  • 18-20% of pregnant women are in abusive relationships
Mothers who are in abusive relationships are four times more likely to miscarry, or to have low birth weight or premature babies, and related health problems.
  • 20.4% (820,000) smoke cigarettes
Cigarette smoking causes a 1.4 – 2.5% increase of low birth weight and related problems, learning disabilities, and cleft lip and/or palette.
  • 25% (1,000,000) are teenagers
Adolescent mothers are 2 to 6 times more likely to have a child with low birth weight or prematurity and its related problems, as well as infant mortality rate and SIDS. Teenagers are also at greater risk for anemia, blood pressure problems, and complicated deliveries.
  • Polydrug use during pregnancy
The NIDA National Pregnancy and Health Survey has uncovered a strong link between cigarette smoking and alcohol use and the use of illicit drugs in this population. Among those women who used both cigarettes and alcohol, more than 20 percent also used marijuana and 9.5 percent took cocaine. Conversely, of those women who said they had not used cigarettes or alcohol, only 0.2 percent smoked marijuana and 0.1 percent used cocaine. "This finding reinforces the need for health practitioners to monitor the status of both licit and illicit drug use during pregnancy," said NIDA director Dr. Leshner.
  • Pregnancy in women over 35 is on the rise
Mothers who are over 35 are thirty times more likely to have a child with Down’s Syndrome. Pregnant women who are 40 or over are one hundred times more likely to give birth to a Down’s Syndrome baby. Such chromosomal defects do not follow any hereditary pattern.

Clearly the evidence proves that legislation against first cousin marriages is an unnecessary measure of prevention. There are far more high risk lifestyles to be concerned with. We, as a society, make use of every opportunity to educate women and couples about how their lifestyle choices can affect their unborn children, while allowing them the freedom of choice. Do first cousins deserve any less consideration?

An Alternative Solution:

While the risk of birth defects is only very slight, it is still something that all first cousin couples should take into consideration. Genetic Counselors are able to determine the margin of risk for a couple by carefully examining the medical history of both sides of the family. In some cases, if a history of genetic disorder is revealed, blood tests can determine whether the couple actually carry the defective gene.

Insurance usually will cover the costs associated with genetic counseling, however, many individuals do not have adequate coverage. Those that do often will not seek counseling for fear of their kinship being exposed, thus making them vulnerable to discrimination and social prejudice. Others may not even realize that medical options exist.

First cousins should be aware of the availability of genetic counseling and testing, and encouraged (but not mandated) to seek the advice of a qualified expert. Information packets could be distributed to any first cousin couple applying for a marriage license, and a voucher program could make counseling more affordable to those who do not have insurance. By providing such information and options, we would be giving cousins the freedom to make an informed decision.

>What do the experts have to say? "In terms of legislation, personally I don’t feel laws against cousin marriages are necessary. I think the legislators could focus on an education program for cousin relationships. Perhaps funding could be found for vouchers for genetic counseling services for those without medical coverage. I don’t feel people should be mandated to see genetic counseling, but every obstacle should be removed to allow them the opportunity."
~ Jacquelyn Krogh, MS, CGC

"We do not restrict people with autosomal dominant disorders such as Huntington disease who have a 50/50 risk to pass the condition to their children from marrying or conceiving! There is no social pathology associated with marrying a cousin and in fact cousin marriages are the norm in many parts of the world…"
>~ Robin L. Bennett, MS, CGC

Buy the book! Click here now!In the near future I would expect more states to make it illegal but, eventually the facts will become known and the trend will reverse. There is no evidence to support the notion that generations of cousin marriage in itself results in genetic problems. The evidence indicates quite the opposite. One must challenge any statements about the dangers of cousins marrying and make people aware of the facts. That way the next generation may give up the myth.
~ Martin Ottenheimer, Professor of Anthropology

I’m not against healthy relationships. I’ve not come across any research to suggest that cousin relationships, between two consulting adults are damaging psychologically in any way. Cousins share an exclusive history with each other. It’s a relationship where you don’t have to create a shared history or experience. You have a head start on intimacy, in a sense the work is already done for you.
~Dr. Robi Ludwig, Ph.D.


Physicians Committee for Responsible Medicine
Journal of the American Medical Association
American Academy of Family Physicians
National Institute on Drug Abuse
Forbidden Relatives

March Of Dimes

Martin Ottenheimer
Jacquelyn Krogh
Ann Stembridge
Alan Bittles

© 2000 Christie Schuler Smith for CUDDLE International and