(876) Low fetal fraction on cell free DNA screening is associated with preterm birth and preeclampsia

Objective: To evaluate the association of low fetal fraction on cfDNA screening with pregnancy outcomes.

Study Design: All patients from 2016-2021 were divided into two groups based on cfDNA fetal fraction results into normal and low fetal fraction ( < 2.8%) groups. Baseline demographics and clinical characteristics were extracted from the medical records. Maternal and neonatal outcomes were collected. Variables were compared using t-test, chi-square, and logistic regression with a statistical significance considered at p < 0.05.

Results: During the study period, 780 patients underwent cfDNA screening: 765 with adequate results, and 15 with a low fetal fraction. Groups were similar when comparing ethnicity, age, parity, BMI, obesity, maternal diabetes, gestational age at time of testing, gestational age at time of delivery, high risk cfDNA results, birth weight, NICU admission, or composite fetal outcomes. Smoking occurred more frequently in the low fetal fraction group (2.2% v 13.3%; p = 0.006) and smoking increased risk for a low fetal fraction result (OR 6.3: 95%CI 1.3–31.1; p = 0.02). The incidence of preeclampsia (5.5% v 26.7%; p = 0.001) and preterm birth (9.7% v 35.7%; p = 0.001) were greater with a low fetal fraction result. In regression analysis, low fetal fraction (OR 3.7: 95%CI 1.1–13.1; p = 0.03) was an independent predictor of preterm birth (Table 1).

Conclusion: Low fetal fraction on cfDNA screening is associated with preeclampsia and preterm birth, both placenta mediated morbidities. Smoking increases risk for low fetal fraction on cfDNA screening.