Multiple Birth Watch

Quadruplets were born to a 55-year-old woman last April. The Associated Press reported on 23 April 1998 that quadruplets (three girls and one boy) had been born to a 55-year-old woman at the Birch Hospital for Women in San Diego, California, five days earlier. According to a spokesman from the American Society for Reproductive Medicine, the woman, who requested that her name be withheld, is believed to be the oldest woman in the United States ever to give birth to quadruplets. The hospital would not disclose the infants' weights, but did reveal that the babies were two months premature and were delivered by Caesarean section. A local television station reported that one of the babies weighed only 10 ounces (280 grams) and was in critical condition. The new mother was not married and had been impregnated by in vitro fertilization. The ethics of fertility treatment for older and unmarried women has been a topic for vigorous debate, and this new case triggered considerable additional controversy. Sadly, on 28 April, Reuters News Service reported that one of the premature neonates, a 10-ounce girl, had died after being disconnected from life support.

From reading the news one is left feeling that there is a competition to produce the largest litter at the latest possible age. Agence France-Presse reported on 2 June 1998 that a 52-year-old Australian woman had given birth to triplets (two girls and a boy) five weeks prematurely on 28 May at Adelaide's Women's and Children's Hospital. The new mom, Wendy Kenyon of South Australia, was believed to be the oldest person to give multiple birth in Australian history. The birth followed from an in vitro fertilization of donor eggs of a friend. The health of the newborns was not reported, but there were no suggestions of problems.

In the U.S., the state of Iowa has recently become an international hotspot for multiple birth. Of course, the birth of the McCaughey septuplets in Iowa last November drew tremendous media attention. More recently, but with somewhat less fanfare, the Associated Press reported on 10 April 1998 of the birth of two sets of quadruplets in two days at the University Hospital in Iowa City. This event would have been noteworthy, but it was made more so by the fact the four girls born to Kimberly and Daniel Grady were genetically identical (monozygotic). Identical quadruplets are extremely rare. Dr. Jerome Yankowitz, head of the University Hospitals' division of maternal and fetal medicine, was quoted as saying, "The odds are at least 1 in 100 million and possibly greater." Unfortunately, the four girls were born 14 weeks premature and none weighed as much as two pounds (900 grams). I have no further information on their health status.

Predictably, the fraternal quadruplets were born to a couple (Jody and Mike Eastridge) undergoing treatment for fertility problems (in this case by in vitro fertilization), whereas the identical quadruplets were a natural event. Monozygotic (MZ) twinning and MZ higher-order births (triplets, quadruplets, etc.) do not occur markedly more often in most forms of infertility treatment. Dizygotic (DZ) twinning and polyzygotic (PZ) higher-order multiple births are much more common in in vitro fertilization and in women taking fertility-enhancing drugs. This is because the drugs increase the number of eggs a woman produces, and multiple eggs may lead to multiple, genetically distinct offspring. In in vitro fertilization, multiple embryos (usually two to six) are implanted to increase the probability that at least one will be successful. The fertility drugs and in vitro techniques have little or no effect on the probability than a zygote will split to form multiple, genetically identical (MZ) offspring. Thus, while the rate of higher-order multiple birth has increased dramatically in recent years, the rate of higher-order MZ multiple birth has been relatively stable.

New Statistics on Multiple Birth in the United States

In the last issue of Twin Research I reported on the availability of data from the National Center for Health Statistics (NCHS; http://www.cdc.gov/nchswww/) on multiple birth in the United States for 1995. The NCHS announced on 30 June 1998 that the data for 1996 are now available as part of their lengthy Report of Final Natality Statistics, 1996. To view the data, go to the web page at http://www.cdc.gov/nchswww/releases/98news/98news/natal96.htm and download the PDF file (you will need the Adobe Acrobat Reader program to view this file-- download this free program from http://www.adobe.com/prodindex/acrobat/readstep.html). The report prints beautifully, but it is 100 pages long, so you might want to print selected pages. According to the report, "The number of twins born in 1996 increased 4 percent (100,750 compared with 96,736 for 1995), while higher order multiple births rose 19 percent to an unprecedented 5,939 (nearly 1,000 more compared with 4,973 in 1995). For comparison, there were approximately 1,000 total higher order multiple births in each year during the 1970s. The higher order multiple birth total included 5,298 triplets, 560 quadruplets, and 81 quintuplets and other higher order multiples. The twinning rate grew by 4 percent (from 24.8 to 25.9 per 1,000) and higher order multiple birth rate by 20 percent (from 127.5 to 152.6 per 100,000) for 1995 96. Since 1980, the twinning rate has risen slightly more than a third (from 18.9 per 1,000) and the higher order multiple birth rate has quadrupled (from 37.0 per 100,000)." p. 2.

Multiple Birth in Armadillos

Genetically identical offspring are anomalies in nearly all animal species (there are a few exceptions among wasps, flatworms and aquatic invertebrates). Genetic diversity of offspring increases the probability that at least some will survive, so the strategy of producing more than one offspring from any single genome is a risky business--putting all of one's eggs in the same basket, so to speak. Those few species that regularly reproduce by creating multiple genetically- identical offspring do it through a process called polyembryony in which a single embryo splits into two or more embryos. (MZ twinning in humans is also accomplished by polyembryony.) Amazingly, only one vertebrate, the armadillo, an American mammal, reproduces regularly by polyembryony. Six species of nine-banded armadillo always produce litters of four genetically identical offspring. The cellular mechanisms through which this remarkable feat is achieved are unknown, but recent research reported by Loughry and colleagues in the May-June 1998 issue of American Scientist (Vol. 86, No. 3, pp. 274-279) sheds some light on how natural selection may have led the armadillo to adopt this unusual reproductive strategy. Loughry and colleagues conducted a series of field studies to determine if armadillos might be benefiting from the altruistic behavior of their genetically identical litter mates. Five years of research led to the conclusion that there was little or no effect of altruism on the survival and reproductive success of armadillos. Anatomical studies of the female armadillo's reproductive tract seem to offer a more promising approach to understanding the evolution of polyembryony than do studies of armadillo behavior. The armadillo uterus is formed such that space allows no more than one blastocyst to implant in the endometrium. This limitation constrains some species of armadillo to one offspring per birth, but in six species of nine-banded armadillo the growing embryo overcomes this limitation by splitting into four identical embryos. Of course, for the female armadillo's reproductive fitness, four offspring are better than one, even if the four are genetically identical. This explanatory theory for polyembryony in the armadillo was first presented by Gary Galbreath of University of Chicago in 1985, and it is the theory most favored by Loughry and colleagues. An abstract and two figures from Loughry et al.'s paper can be viewed at http://www.amsci.org/amsci/articles/98articles/loughry.html along with other information about armadillos and their reproductive habits.

Web Watch

All URLs (web addresses) presented in this author's News and Views articles are also presented as links in a web page at http://taxa.psyc.missouri.edu/twinnews/ so that interested readers can "point and click" to get to the web-based materials instead of typing the URLs. In addition to these links, the web page includes links to some of the news and journal sources cited in the paper.

The author also maintains a e-mail list called BGnews on which he transmits messages about news reports of new research findings in behavior genetics and twin research. Much of the news presented above was announced on the mailing list at the time it was first disseminated. To get an idea of what BGnews messages are typically like, browse the BGnews archives at http://taxa.psyc.missouri.edu/bgnews/. If you would like to subscribe to this e-mail list, simply send an e-mail message to mbmiller@taxa.psyc.missouri.edu with the single word 'subscribe' in the "Subject:" field, and no message text.

Readers with a general interest in twins might like to browse the web sites devoted to twins and twinning that have been indexed in the Yahoo! directory at http://www.yahoo.com/Society_and_Culture/Families/Multiple_Births/Twins/. From this site one may link to the web pages of several organizations for parents of twins, to sites offering products and services for twin families, a usenet news group for parents of twins, and much more.