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Bridgewater, NJ
OCTOBER 2005
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In Learn More the National Geographic magazine team shares some of its best sources and other information to expand your knowledge of our featured subjects. Special thanks to the Research Division.
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 Did You Know?
The Yoruba people of southwestern Nigeria have the highest occurrence of twinning in the world. With 45 twins for every 1,000 births, the rate is almost four times the world average. No one knows why, but there are many theories.
The most surprising explanation points to diet. While some women in Bridgewater, New Jersey, take fertility drugs, most women in towns like Igbo Ora, the self-proclaimed land of twins, eat agida. This local yam variant, a staple in the Nigerian diet, is believed to stimulate egg production.
In 1998 a group of obstetricians from Yale University, led by Frederick Naftolin, in conjunction with obstetricians from the University of Benin in Nigeria, decided to test the idea. Kunle Odunsi, one of the researchers, says evidence suggests that yam consumption does indeed correlate with twinning rates. "In some societies people eat a lot of yams, kind of like having hamburgers," Dr. Odunsi says. "Mothers of twins are more likely to eat yams for breakfast, lunch, and supper."
Based on this unpublished research and on lab results, Dr. Odunsi and his colleagues think there is a chemical in these yams similar to clomiphene citrate, a fertility drug used to encourage ovulation. This chemical has not yet been extracted or tested.
Dr. Odunsi says the researchers also found that twinning rates are higher in older mothers who have had previous pregnancies. Genetics may also play a role. Skeptics of the yam theory attribute the high twinning rates in Nigeria and other African countries to a combination of other factors.
The incidence of twins varies by race. Africans have the highest rate worldwide, Asians the lowest.
—Elizabeth Quill
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Related Links
American Society for Reproductive Medicine
www.asrm.org
Patients and professionals with an interest in infertility and reproductive medicine will benefit from the information on this website, including the "Find a Doctor" feature.
American Fertility Association
www.theafa.org
The AFA works to raise awareness of infertility issues and provides information about medical treatments, legal and insurance concerns, and support services. Contact the association for one-on-one support and referrals to professionals.
National Infertility Association
www.resolve.org
This 30-year-old advocacy group focuses on educating and supporting men and women experiencing the challenges of infertility. Physician referral services, a member-to-member contact system, and publications about infertility can be found here.
National Organization of Mothers of Twins Clubs, Inc.
www.nomotc.org
A network of hundreds of local clubs representing over 23,000 parents, this organization is a leader in promoting child development relating specifically to multiple-birth children. If you have twins, triplets, or more—or are expecting soon--visit this website to find a club near you.
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Bibliography
American Society for Reproductive Medicine. Multiple Pregnancy and Birth: Twins, Triplets, and Higher Order Multiples—A Guide for Patients. 2004. Available online at
www.asrm.org/Patients/patientbooklets/multiples.pdf.
Centers for Disease Control and Prevention and American Society for Reproductive Medicine. 2002 Assisted Reproductive Technology Success Rates: National Summary and Fertility Clinic Reports. U.S. Department of Health and Human Services, December 2004. Available online at www.cdc.gov/reproductivehealth/ART02/index.htm.
Laut, William, Kristin Benit, and Sheila Laut. Raising Multiple Birth Children: A Parents' Survival Guide. Chandler House Press, 1999.
Luke, Barbara, and Tamara Eberlein. When You're Expecting Twins, Triplets, or Quads: Proven Guidelines for a Healthy Multiple Pregnancy. HarperResource, 2004.
Moskwinski, Rebecca, ed. Twins to Quints: The Complete Manual for Parents of Multiple Birth Children. Harpeth House Publishing, 2002.
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NGS Resources
Rossi, Ann. Voices "From Colonial America: New Jersey, 1609-1776." National Geographic Books, 2005.
Newman, Cathy. "Greetings From the Jersey Shore." (August 2004), 80-99.
Phillips, Angus. "ZipUSA: Ocean Grove, New Jersey." (August 2001), 122-6.
Peffer, Randall. Driving Guides to America: New York and Pennsylvania and New Jersey. National Geographic Books, 1997.
Hart, Jim. "New Jersey: A State of Surprise." National Geographic (Novemeber 1981), 568-99.
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