“Intrauterine growth in twin and singleton births in relation to fetal and maternal factors”
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Background: The aim of this study was to present a growth curve for estimated fetal weight (EFW) of twins, stratified for chorionicity, and compare it to that of singletons. We also wanted to assess if maternal factors known to affect growth differed between singletons and twins, and furthermore between monochorionic (MC) twins and dichorionic (DC) twins. Methods: We used data from the Scandinavian SGA study, a prospective, population based study, collected between 1986-88. Our two cohort groups, a singleton group (n=560) and a twin group (n=31), were followed with four serial ultrasound examinations during the 2nd and 3rd trimester. The fetal measures were mean abdominal diameter (MAD), biparietal diameter (BPD) and femur length (FL), which were then used to calculate estimated fetal weight (EFW) using a formula by Hadlock. Then we estimated separate growth curves for singletons, MC twins and DC twins using an algorithm previously published by Villandré et al. We also assessed if maternal age, smoking, BMI and previous spontaneous abortion influenced the three growth curves, and if the degree of influence differed between them. Results: The curves demonstrated that the growth of twins decreased in growth compared to singletons from gestational week 30, and that MC twins decreased more than DC twins. Regarding the birth outcome we found that twins had a shorter gestation and were smaller at birth than singletons, but that there were no differences between MC and DC. We found a significant increase in effect on growth of increase in maternal BMI on the MC twins, and significantly more on the MC compared to the DC twins. The growth of singletons decreased significantly from both maternal smoking and increasing BMI, and this was significantly different from the effects on DC. Interpretation: We have shown, as other studies, that the twin growth is lesser than the singletons’ from week 30, and that MC have a more decreased growth than DC. As expected the singletons had a significant response to both smoking and BMI, but what is more interesting is that the DC had a significantly lesser effect on both of these variables.