Examining the predictive value of fetal fraction on hypertensive disorders of pregnancy.

BACKGROUND

Cell-free fetal DNA (cffDNA) screening is routinely performed in pregnancy. Abnormal fetal fraction has been associated with adverse pregnancy outcomes, including hypertensive disorders of pregnancy, which are associated with severe maternal and neonatal morbidity and mortality.

OBJECTIVE

This study examined whether abnormal fetal fraction, defined in this study as fetal fraction either <6 or >15 on the basis of restricted-cubic-spline-plot within our study population, was associated with HDP in a retrospective sample, as well as whether fetal fraction improves the prediction of hypertensive disorders of pregnancy (HDP). We hypothesized that abnormal fetal fraction would be associated with HDP and that adding fetal fraction to a model would significantly improve its strength to predict HDP.

STUDY

DESIGN

This was a retrospective cohort study of 729 patients delivering singleton, non-anomalous pregnancies with conclusive cffDNA screening. The primary outcome was HDP. Logistic regression models tested associations between fetal fraction and HDP. We evaluated the impact of including fetal fraction on the prediction of hypertensive disorders of pregnancy (HDP) by comparing the area under the receiver operating characteristic (ROC) curve (AUC) between predictive models with and without fetal fraction.

RESULTS

Among the study sample, there was an HDP rate of 11.5 %. Abnormal fetal fraction was defined as <6 % percentile and >15 %, HDP incidence was significantly higher in patients with fetal fraction <6 % compared to patients with fetal fraction in normal range (fetal fraction 6-15 %) (19.5 % vs 10.7 %, p = 0.006 on post hoc comparison). Model 1 had one predictor (fetal fraction) with an AUC of 0.59, Model 2 had three predictors (BMI, nulliparity, history of HDP) with an AUC of 0.71, and Model 3 had four predictors (BMI, nulliparity, history of HDP, and fetal fraction) with an AUC of 0.73. Models 2 and 3 were not significantly different (p = 0.18).

CONCLUSIONS

More patients who developed HDP had low fetal fraction and fewer patients who developed HDP had high fetal fraction compared to those patients who did not develop HDP. Based on results from multivariable regression models, we cannot conclude that fetal fraction improves HDP prediction. However, developing standardized values for abnormal fetal fraction may be clinically useful.