Insulin sensitivity and abdominal fat mass both have been reported to be inversely related to
birthweight differences within twin pairs, with a one standard deviation increase in birthweight associated with a 16% decrease in insulin sensitivity in elderly twins and with a 3.2 volume/%
decrease in intra-abdominal fat mass in young twins.Thus, twin conception, a naturally occurring phenomenon, is associated with altered fetal growth and endocrine development with consequences for life-long metabolic health. This has implications not only for the epidemic of twins that has accompanied assisted reproductive techniques but potentially also, as the origins of these effects appears to be in early pregnancy, for our understanding of the fundamental mechanisms that underlie these
observations