Women who have twins naturally may live longer and have other child-bearing advantages compared with non-twin-bearing mothers, a study finds.
But before assuming that having twins gives women a health advantage, researchers believe the reverse might be true, that being healthier could give women better chances of having twins.
The study, released online Tuesday in the journal Proceedings of the Royal Society B, used statistics on 58,786 women who were born between 1807 and 1899--a group that didn't have fertility treatments or artificial birth control at their disposal. The women also lived to at least 50 years old, and were married once after 1850 to men who were alive when their wives were 50. Of those women, 4,603 had twins and 54,183 did not. Women in polygamous marriages were not included.
The data came from the Utah Population Database. For the study women were divided into two categories: those born before 1870 and those born from 1870 to 1899, to distinguish, as the authors wrote, "the natural fertility era from the early stages of fertility planning."
Researchers from the University of Utah in Salt Lake City discovered that twin-bearing mothers lived longer after menopause--women born before 1870 had a 7.6% lower mortality risk after 50 compared with non-twin-bearing moms (twin-bearing moms born between 1870 and 1899 had a lower risk also but it was not significant).
Mothers of twins had more children overall compared with non-twin-bearing moms by virtue of their multiple births, but they also had more single children than moms of single babies.
Twin-bearing moms also had slightly shorter time spans between having children. Among all women in the study, the average time between births was 2.62 years for women born pre-1870, and 3.24 years for women born between 1870 and 1899. Having twins cut the intervals by two weeks.
Mothers of twins won again in the length of their reproductive period. Those born before 1870 had an average span of 18 years, four months, while the period for non-twin-bearing moms was 18 years. For women born from 1870 to 1899, the spans were 14 years, 11 months compared with 14 years, respectively.
Twin-bearing moms tended to be a little older than non-twin-bearing mothers when they had their last baby--about 4.8 months older for those born pre-1870, and 14 months older for those born from 1870-99.
"The prevailing view," said senior author Ken Smith in a news release, "is that the burden of childbearing on women is heavier when bearing twins. But we found the opposite: women who naturally bear twins in fact live longer and are actually more fertile."