Supplementary Material for: Gender-Specific Antenatal Growth Reference Charts in Monochorionic Twins

<b><i>Objective:</i></b> To create antenatal gender-specific reference growth charts in uncomplicated monochorionic diamniotic twins. <b><i>Materials and Methods:</i></b> This is a prospective longitudinal study in which uncomplicated monochorionic (MC) twin pregnancies were included from 23 + 4 weeks of gestation onwards. Estimated fetal weight (EFW) and biometric parameters (biparietal diameter, head circumference, abdominal circumference, and femur length) were evaluated in both fetuses every 2 weeks using standardized methodology. Maternal and fetal complications were excluded. Charts were fitted for each biometric parameter and EFW in relation to gestational age and fetal gender using multilevel mixed models. <b><i>Results:</i></b> The final analysis included a total of 456 ultrasound examinations in 62 MC twins, with a mean of 7 scans per pregnancy (range 5–8). The mean as well as 5th and 95th percentiles of each biometric parameter and EFW were adjusted in relation to gender and gestational age between 24 and 37 weeks of gestation. Male fetuses have higher reference values than females, and the disparity is larger in the upper centiles of the distribution. <b><i>Discussion:</i></b> We provide gender-specific reference growth charts for MC twins. We suggest that these charts will improve prenatal MC twin assessment and surveillance, with a more accurate classification of normal or growth-restricted fetuses adjusted per sex.