New Stats on Twins: Double the Odds

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Since 1980, there has been a dramatic and surprising increase of multiple births in the United States. Interesting research is emerging on many levels, from maternal and neonatal health, to a variety of public health issues.

The odds are increasing that a woman in the U.S. will have twins, triplets, or some form of multiple birth. That’s the finding of a study jointly conducted by the Centers for Disease Control and Prevention and the Department of Obstetrics, Gynaecology and Reproductive Biology at Michigan State University’s College of Human Medicine.

Researchers compared statistics on live multiple births from 1980 and 2009 and came up with some surprising findings. The odds of having a twin almost doubled (from one in 53 in 1980, to one in 30 in 2009), and the odds of having triplets more than tripled (from one in approximately 2700 in 1980, to one in 651 in 2009). MSU researcher, Dr. Barbara Luke, who presented her findings at the 14th Congress of the International Society of Twin Studies in Florence, Italy, attributes approximately one third of the rise in multiple birth rates to increased maternal age at conception, and approximately two-thirds of the increase to the use of fertility drugs. The rates for multiple births had been stable for many years prior to 1980 (at an approximate average of 2 percent of all live births), so the increase in rates over the last few decades has been nothing short of dramatic.

Carrying multiple fetuses brings increased health risks to mothers, and poses additional risks during the birth process as well as postpartum development. And presently, close to 12 percent of mothers undergo some type of fertility enhancement procedure, which increases the chance of multiple births. That’s why researchers like Dr. Luke at MSU and her colleague Joyce Martin at CDC are working so hard to better understand the connection between fertility treatments and various increased health risks. A previous study, for example, found that the loss of an embryo early in a multiple pregnancy significantly impacted the birth weight and survival rate for the remaining fetuses. Other factors are sure to be uncovered as well. But as advances continue in both prenatal and neonatal care, and as we come to better understand the overall impact of fertility treatments, the rates for multiple births will probably only increase over their already higher than normal level.

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Twins have long been a source of interest not only for medical scientists, but also for the average person. Identical twins especially pique our interest. As opposed to “fraternal” or “sororal” (dizygotic) twins, that develop from two separate eggs fertilized by different sperm, identical (monozygotic) twins develop from the same fertilized egg, that for some reason splits into two separate embryos. And these twins can provide us with invaluable information about the roles of genetic, hormonal, environmental, and lifespan factors in areas of concern in public health, such as the propensity for various diseases, neurobiological development, psychological functioning, and the formation of personality patterns. That’s one of the reasons why research centers like the one at Michigan State University have created twin registries. Twins not only fascinate us, but also provide us with a wealth of information about the genetic and environmental influences on our health and behavior.

I must confess a special interest in twins. I myself am a twin, and an identical twin, at that. My brother died shortly before he was born, and according to the doctor, I was very fortunate to have survived. And while all this happened long before I could remember anything, I often found myself in childhood musing about what it would have been like to grow up with a carbon-copy companion — someone who looked like, talked like, and perhaps even acted like myself. So, as fascinating as twins are in general, they hold a somewhat special fascination for me.

With multiple birth rates increasing, the odds of having twins almost doubling, and survival rates steadily improving, the chances are quite good that there will be a substantial increase in valuable information compiled by twin research centers across the country over the next few decades. And although the vast majority of twins will still be non-identical, our knowledge about the role of genetic factors in human development and functioning should still improve. I for one will be watching the research carefully. Twins will always hold a unique interest for me, and it’s always a bit special when I come across a surprising new finding that emanates from twin research.

All clinical material on this site is peer reviewed by one or more clinical psychologists or other qualified mental health professionals. This specific article was originally published by on and was last reviewed or updated by Dr Greg Mulhauser, Managing Editor on .

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