Intrauterine growth in twin pregnancies

Multiple pregnancies have always been the subject of intense medical and social interest, representing a unique opportunity for determining the relative contributions of genetic and environmental influences upon human growth and development. Birth statistics for the year 2003 show that the multiple birth rate in England & Wales is 1.5% of all maternities. In the past two decades it has increased by 50% in England and Wales (1) and by 74% in the United States (2). Although one-fourth of this is due to child bearing among women of older ages, three-fourths is due to infertility treatments and assisted reproductive techniques (3). The combined effects of congenital anomalies, premature deliveries, maternal antenatal complications and low birth weight ensures that the perinatal mortality for multiple pregnancies remains considerably higher than that of singletons despite advances in perinatal care. Preterm delivery and intrauterine growth restriction are the leading causes of poor outcome in twin pregnancies (4). There is a larger increase across weight categories for a given gestational age than across gestational ages for a given birth weight (5). Twins are almost 10 times more likely than singleton to have a low birth weight (< 2500 g or < 1500 g) and their mean birth weight is approximately 1000 g less than that of singletons (2400 compared with 3400 g). This weight difference compared with singletons caused by slower growth and by birth at earlier gestations in approximately equal measures. Controlled for gestational age, twins weigh approximately 500 g less at term. Hence accurate prenatal assessment of the size of twins is essential in preventing perinatal death. There is a need for greater understanding of twin pathophysiology, including growth, and adoption of effective management strategies. Twins and lenght of pregnancy