New reference values for biometrical measurements and sonographic estimated fetal weight in twin gestations and comparison to previous normograms

Abstract

Objective To construct new reference values for biometrical measurements and sonographic estimated fetal weight (sEFW) in twin gestations and compare them to previously published normograms. Methods A retrospective analysis of sEFW evaluations of twin gestations was performed between 2011 and 2016 in a single university-affiliated medical center. sEFW was calculated using the Hadlock 1985 formula. To avoid selection bias, one evaluation per pregnancy was randomly selected. Following mathematical transformation to obtain normality of values, normograms were constructed using a best-fit regression model for estimation of mean and standard deviation at each gestational age (GA). Normograms were validated by applying all observations to ensure equal distribution at parallel percentiles. Our normograms were then compared to previously published sEFW normograms for twin gestations. Results A total of 864 sEFW evaluations were performed on 195 twin pregnancies at 22–39 gestational weeks. Of them, 390 entered the primary analysis. The rest were left for validation. Seventy percent of the cohort were dichorionic-diamniotic twins (136/195), 16% (32/195) were monochorionic-diamniotic twins and three (1.5%) were monochorionic-monoamniotic twins. Twenty-four fetuses lacked data on chorionicity. The rest were monochorionic twins or were of unknown chorionicity. Values corresponding to the 2.5th, 10th, 50th, 90th and 97.5th percentiles for sEFW are presented for every GA. Validation by applying all 864 evaluations on constructed normograms was achieved. Comparison to previously published twins’ sEFW normograms demonstrated wide variation between curves. Conclusion New reference values for biometrical measurements and sEFW in twin gestations are presented for clinical and research use. Comparison to other curves demonstrates the wide variability and need for further investigation on twin’s normal growth.

Fetal Medicine Foundation charts for fetal growth in twins

“…To compare the FMF twin growth models presented in this study with findings of other studies, we collected details from nine previous models, based on a total of 6152 DC twin pregnancies (n per study ranged from 136 to 1802), 1920 MCDA twin pregnancies (n per study ranged from 32 to 688) and 884 twin pregnancies without information regarding chorionicity (Figure 5) [12][13][14][15][16][17][18][19][20] . The pattern of growth, relative to the FMF singleton growth charts, was similar to that of our model in three of the nine published models [14][15][16] .…”

Twin charts should be the standard reference to assess growth in twin pregnancy

“…On the other hand, given that the growth velocity of twins and singletons are similar in the second trimester, it might be considered that the growth lag seen in twins in the third trimester is likely to be pathological because of uteroplacental insufficiency or other extrinsic factors, continued use of singleton growth standards may be deemed appropriate [30]. Several twin-specific charts have been developed by various investigators [19,25,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]48 && ,49,50], and with emergence of evidence citing superiority of twinspecific standards, an increasing number of professional societies appear to be endorsing twin-specific standards to monitor growth in twin pregnancies. For example, the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends the use of twin-specific growth standards, while expressing concern that reduced foetal growth velocity in the third trimester in twin pregnancies may also include a component of uteroplacental insufficiency, which warrants closer surveillance [22].…”

Fetal Growth and Antenatal Testing in Uncomplicated Multiple Gestations

“…Several investigations have examined the growth of individual fetal biometrics in multiple gestations. [6][7][8]14 Compared with singleton counterparts, the greatest disparity in twin growth is found in the abdominal circumference (AC). Most notably, the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)-Fetal Growth Study prospectively followed 171 dichorionic (DC) twins and 2334 women with low-risk singleton pregnancies.…”

“…Several investigations have examined the growth of individual fetal biometrics in multiple gestations 6–8,14 . Compared with singleton counterparts, the greatest disparity in twin growth is found in the abdominal circumference (AC).…”