By Minnie Apolis
In an informal discussion with a school employee in southern Minnesota, I found that Minnesota may have not one but two hot-spots where twins are born in high numbers.
Recently I was helping out a woman who works in the the education field. I had noticed some names in a list of students where two apparent siblings had names that rhymed or started with the same letter. I asked this woman if there were a lot of twins in the area.
She was not sure if there were statistically more than normal, but she said that her child was in a class with TWELVE twins. Oops, not twins, I meant to say twelve SETS of twins.
While Minnesota is not in the top ten as far as statistics on twinning go, it is amazing to me that the eighth grade in Albert Lea boasts an even dozen sets of twins. It is even more amazing that they do not hold the current record – upstate Bemidji has fourteen sets of twins in one grade level.
In 2009, the twin birth rate was 33.2 per 1,000, up from only two years ago. In 2007 the twin birth rate was 32.2 per 1,000 nationally, which did not represent any increase over the previous two years. However, there has been a decrease in multiple births in general. The rate was a whopping 176.9 per 100,000 live births in 2004, but only 148.9 per 100,000 live births in 2006.
Twinning rates by race:
In 2007: Non-Hispanic whites had twins at 36.2 per 1,000 births. Non-Hispanic blacks had 36.8 per 1,000 births. Hispanics had a mere 22.2 twins per 1,000 births. In 2009: Non Hispanic white had 37 twins per 1,000 births. Non-Hispanic blacks had 38 twins per 1,000 births. Hispanics had 22.5 twins per 1,000 births.
Older moms were more likely to have twins – 20 percent of births to women over age 45 were twins, but only 2 percent of teen moms had twins.
For the years 2005-2007, twins accounted for more than 4 percent of all births (that is, over 40 per 1,000) in Massachusetts, Connecticut, and New Jersey. (The above data from http://multiples.about.com/od/funfacts/a/twinbirthrate.htm)
Twinning is Increasing
Interestingly, About.com notes that “the twinning rate rose sharply between 1980 and 2004 (from 18.9 to 32.2) but has been fairly stable in the years since. (http://multiples.about.com/od/funfacts/a/Twin-And-Multiple-Birth-Rate.htm) What could be the reason for that? One reason is the continued delay in starting a family, since older moms are more prone to having twins. Another is that perhaps more women are resorting to fertility drugs to get pregnant in later years.
[2004 Statistics on Twinning nationally and by state: http://www.twinstuff.com/twin-facts/145-twinning-rates]
It is generally believed that in Caucasian populations the rate of monozygotic (MZ) twinning is approximately equal to the rate of like-sex dizygotic (DZ) twinning so that representative samples of like-sex twins should contain approximately equal numbers of MZ and DZ twins. Recent evidence suggests, however, that the rate of DZ twinning in Caucassian populations has declined over the past 50 years so that there are now many more MZ than like-sex DZ twin births (Jeanneret and MacMahon, 1962; James, 1972; Mostelleret al., 1981; Doherty and Lancaster, 1986; Lykkenet al., 1990). We report additional evidence of a higher rate of MZ than like-sex DZ twinning from Minnesota for the birth years 1971–1984. The convergence of evidence thus suggests that the observation of a greater number of MZ than DZ twins in a volunteer twin sample can no longer necessarily be taken as a sign of ascertainment bias.