Having two babies at once is associated to a longer life, according to a new study. But it is not because doubling on dirty diapers increases the duration of life; Instead, the mothers of twins are physically stronger in the first place.
Capture one: research published today (May 10) in the case in the journal of the Royal Society B, based on a population of "natural fertility" women in Utah for the 19th century, the results may not apply in the today of the world of fertilization in vitro (IVF).
However, the findings suggest that rather than being a reproduction accident which drains energy and nutrients, twin mom may be an evolutionary adaptation in which mothers take the chance to spend on the double their genes.
"We expected the exact opposite," researcher study Shannen Robson of the University of Utah told LiveScience. "We expected that since most humans have a baby at the time, having both would be really heavy...". [Twins] are an identifier of these women who are physically exceptional and remarkable people. ?
Natural fertility
Identical twins, created when an embryo is divided into two development, appear more or less randomly. But the twins, which develops from two eggs separate released and fertilized at the same time, shows some two heritability models - they ran in families - and the influence of the environment. Not including the twins designed from IVF, account of twins for every 1,000 births in Asia 6, 10 to 20 of every 1,000 births in Europe and the United States and 40 with every 1,000 births in Africa.
To look at before matching techniques of reproduction and reliable contraception, the team used the Utah Population Database, a huge genealogical record of the residents of Utah dating from the beginning of the 19th century. The database, they taken from the family archives of women who were born between 1807 and 1899 and who lived up to at least 50, so that they have experienced their full range of child-bearing. Excluded widows and wives in the polygamous families to ensure that they were comparing similar women. [History and the future of birth control]
The result was a database of women 58,786, 4,603, who had at least a set of twins. The researchers compared the Moms of twins with the mothers of the singletons, for differences in life expectancy, the number of children, the time between pregnancies and the length of fertility, all measures of health.
Double the pleasure
Flight from the hypothesis that double pregnancy Vienna undermine the strength of women, the researchers found that MOM of twins beat moms only singletons on all measures. They live longer, had more long durations of reproductive life, required less time to recover between pregnancies and had more children together. The mother of twins born before 1870 had averaged 1.9 more children that the mothers of singletons in their age group and Moms in the post-1870 Group had 2.3 children more than their counterparts of mom singleton.
Because the twins have a higher risk of death than singletons, researchers have adjusted this conclusion by the rate of infant mortality, assuming that a MOM of twins may have more babies soon after the death of a child. After this adjustment, moms of twins still out before him, having 1.24 to 1.56 babies more than singleton only moms. That outweighs the effect "plus one" you get to have twins, said Robson.
The results vary with time, even if women pioneers in Utah pre-1870 had worse than born women medical care after. It is difficult to compare the data of the 19th century to our days however, Robson said. IVF has increased the number of twins. And other factors have also changed: women have less overall pregnancies now than women in the 19th century in Utah, so their overall chances of a spontaneous twin pregnancy are lower. A 2001 study of women in rural areas in the Gambia, however, found that mothers of twins had better reproductive health that mothers of only singletons. [Read: 5 myths about fertility treatment]
Robson and his colleagues now hope to watch the twins of women of Utah, to see how they behaved given the twins are more likely to be premature and have health problems. They also hope to look more closely at the supermoms which birth of twins.
"By their identification, we can then look at other aspects of what is on them that makes them healthier, live longer and have babies at a faster pace than everyone in the population," Robson said.
You can follow LiveScience senior editor Stephanie Pappas on Twitter @ sipappas. Follow LiveScience to the latest science and discoveries on Twitter @ livescience and on Facebook.
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