An increase in the fetal fraction can be associated with birthweight discordance and selective fetal growth restriction

Abstract

Abstract Background Twin pregnancies are more likely to be affected by complications such as selective fetal growth restriction (sIUGR) which increase the risk of perinatal mortality and morbidity. Identifying those pregnancies likely to be affected by eiher sIUGR or birthweight discordant early can optimize counseling, the timing of interventions and may, in future, allow trials of preventative treatments. Objective The onset of sIUGR often correlates with increased levels of cell-free fetal DNA (cffDNA). Here we tested the hypothesis that the fetal fraction (FF) in twin pregnancies can reflect discrepancies in the birthweights. Study design : This is a retrospective study of 237 twin pregnancies who underwent cffDNA screening for aneuploidy and delivered at the International Peace Maternity and Child Health Hospital in Shanghai between January 2018 and December 2021. The FFs and birthweights of the newborns were collected and analysed. Results The FF was found to be positively correlated with the difference of birthweights (β = 0.004, 95%CI: 0.001 ~ 0.006). For every 1% increase in the FF, the difference in the birthweight between twins increased by 0.4%. A higher FF was significantly associated with an increased risk of birthweight discordance of 20% (adjusted OR: 1.073, 95% CI: 1.009 ~ 1.142), 25% (adjusted OR: 1.092, 95% CI: 1.006 ~ 1.185) and sIUGR (adjusted OR: 1.130, 95% CI: 1.038 ~ 1.231). Using ROC analysis, we obtained optimum cut-off points for FFs ≥ 11.790 and ≥ 14.800 for birthweight discordance of 20% and sFGR, respectively. Compared with women with FFs of < 11.790, there were a 1.091-fold higher risk of birthweight discordance of 20% (adjusted OR: 2.091, 95% CI: 1.218 ~ 3.591) when the FF was ≥ 11.790. There were also significantly increased risks of birthweight discordance of 25% (adjusted OR: 3.045, 95% CI: 1.297 ~ 7.149) and sFGR (adjusted OR: 3.526, 95% CI: 1.443 ~ 8.618) among women with FFs of ≥ 14.800. Conclusions This study showed that the FF was positively correlated with differences in birthweights. In addition, the FF could be used as an indicator to predict birthweight discordance and sIUGR for individualized clinical monitoring of twin pregnancies.