The Importance of Plasma Volume Expansion and Nutrition in Twin Pregnancy

Abstract

The exaggerated physiological adaptation to pregnancy in women bearing twins is exemplifed by the increased plasma volume in both primigravidas and multiparas, as compared to singleton pregnancies. There is a significant relationship between birth weight and plasma volume in both primigravid and multiparous singleton pregnancies and in multiparous twin pregnancies but not in primigravid twin pregnancies. This paper considers the relative importance of plasma volume expansion, maternal nutrition (particularly zinc), and birth weight in twin pregnancies. One hundred seventeen primigravid twin pregnancies with deliveries after 37 weeks of gestation were studied. The pregnancies were divided into three groups: those in which the mothers were normotensive, those in which they had mild preeclampsia, and those in which they developed proteinuric preeclampsia. There was a significant relationship between plasma volume and birth weight in primigravid twins whose mothers had mild preeclampsia. In primigravid twins whose mothers were normotensive, the association was almost identical with that in multiparous twin pregnancies, but, on account of the greater scatter of values, the correlation coefficient was not significant at 0.29. There was no positive relationship between plasma volume and birth weight in twins whose mothers had proteinuric preeclampsia. The results from twins of normotensive mothers and those whose mothers had mild preeclampsia were combined. There was a significant relationship between plasma volume and the combined birth weights of twins born after 37 weeks of gestation to primigravidas. The 117 primigravid twin pregnancies were divided according to presence or absence of preeclampsia and allocated to the appropriate birth weight centile categories (Table 1). In the total group, there was an over-representation of those under the 25th centile, with fewer in the intermediate categories. In those who were normotensive, 40 per cent were under the 25th centile, but in those with mild preeclampsia there was over-representation in the intermediate category (50th to 75th centile; 36 per cent). In proteinuric preeclampsia, as expected, nearly 47 per cent were under the 25th centile birth weight. When twins of normotensive pregnancies and those of mildly preec-lamptic pregnancies were grouped together, there was still a greater than expected proportion over the 25th centile (35 per cent).