The association between the amount of fetal fraction in cell-free DNA testing and adverse pregnancy outcomes: A cohort study.

Background: Noninvasive perinatal testing is a new method of screening for aneuploidy called cell-free DNA (cfDNA). Fetal fraction (FF) plays a crucial role in assessing the reliability of aneuploidy detection through noninvasive perinatal testing.

Objective: We aimed to investigate the association between the amount of FF in cfDNA testing and adverse pregnancy outcomes.

Materials and methods: This cohort study was conducted on 619 singleton pregnant women who were candidates for cfDNA testing and were referred to the perinatology clinics of Shariati hospital and Arash Women's hospital, both affiliated with Tehran University of Medical Sciences, Tehran, Iran from March 2019 to June 2020. The FF was extracted from the cfDNA test results, and the participants were followed until delivery.

Results: A total of 619 singleton pregnant women with a mean $\pm$ SD age and FF of 34.4 $\pm$ 4.85 and 8.39 $\pm$ 3.95, respectively, participated in the study. A significant association between maternal age and FF was not found (p = 0.12). A lower FF was associated with a rise in the incidence of gestational diabetes mellitus (p = 0.02) and a higher FF was associated with a rise in the incidence of fetal growth restriction (p $<$ 0.001). However, high or low FF was not associated with pre-eclampsia, premature rupture of membranes, birth weight, or delivery time. No significant association was found between FF and multiple of the median of pregnancy-associated plasma protein-A and free β-human chorionic gonadotropin.

Conclusion: The amount of FF may be considered a predictor of certain adverse pregnancy outcomes. Therefore, maternity care should be performed more carefully for women with high or low FF.