Association of fetal fraction and cell-free fetal DNA with adverse pregnancy outcomes: A systematic review

Background: Adverse pregnancy outcomes, which can be caused by multiple factors, present a significant threat to the health of mothers and their babies. Cell-free fetal DNA (cffDNA) from placental trophoblast cells might be able to reflect placental and fetal status. Previous studies have yielded controversial results regarding the association of FF or cffDNA with various adverse pregnancy outcomes. A previous study has attempted to systematically assess the association between low fetal fraction (FF) and adverse pregnancy outcomes, but it failed to perform quantitative analyses due to the few studies included. In the present study, we attempted to quantitatively assess the association of FF (or cffDNA) with adverse pregnancy outcomes and further analyze the causes of heterogeneity.

Objectives: To investigate the association of high/low FF or cffDNA with adverse pregnancy outcomes.

Search strategy: We searched the databases of PubMed, Embase, Cochrane, and Web of Science from January 1, 1990, to June 15, 2022 in this meta-analysis.

Selection criteria: Studies on the relationships of adverse pregnancy outcomes in women with FF or cell free DNA were included. Non-English literature was excluded.

Data collection and analysis: Data about pregnancy outcomes and cell free DNA were extracted and meta-analyzed. Subgroup analysis was performed by different outcomes.

Main results: There were 11 studies included involving 8280 participants. No significant heterogeneity was observed among the studies (I² = 27%, 25%), and a fixed-effect model was used for weighted quantitative analysis. The results revealed that the FF or cffDNA during pregnancy was significantly associated with adverse pregnancy outcomes in pregnant women (OR = 1.57, 95% CI [1.24, 1.99], P = 0.233). The overall incidence of the maternal adverse outcomes was 8% (95% CI: 5-13). Subgroup analysis of different outcomes showed an evident association between low FF or cffDNA and hypertensive disorders of pregnancy (HDP) (OR = 1.76, 95% CI [1.36, 2.27], P = 0.581). There was no evidence that the occurrence of spontaneous preterm birth (sPTB) and placental abnormality was associated with FF or cffDNA. No association was observed between low FF or cffDNA during pregnancy and adverse outcomes in fetuses (OR = 1.39, 95% CI [0.99, 1.94], P = 0.242). The overall incidence of adverse outcomes in fetuses was 8% (95% CI: 6-11). There were controversies over the association between high FF or cffDNA and HDP, and sPTB and small for gestational age infant, among different studies.

Conclusions: Pregnant women with low FF or cffDNA during the first or second trimester of pregnancy have an overall increased risk of adverse pregnancy outcomes, especially HDP. However, the association between FF and various pregnancy outcomes needs to be further explored by more prospective studies.