The effect of abnormal placentation on maternal serum fetal fraction of cell-free DNA.

OBJECTIVES: Abnormal placentation may affect the maternal serum fraction of cell-free fetal DNA (fetal fraction) determined as part of non-invasive prenatal screening (NIPS). This study aimed to assess whether the fetal fraction can predict placenta accreta spectrum (PAS) with or without placenta previa (PP). We also investigated the impact of trophoblastic invasion depth on the fetal fraction. METHODS: This is a retrospective case-control study of pregnant women with and without abnormal placentation carrying a singleton and having undergone NIPS prior to 20 weeks of gestation. The eligible subjects were selected from a cohort managed at our institution for PAS suspected antenatally. We compared women with normal placentation (controls) to PAS, PP, or PAS + PP cases. Data were abstracted from electronic medical records, and PAS was confirmed histologically. RESULTS: Of the 146 patients in our cohort, 8 controls, 10 PP, 6 PAS, and 7 PAS + PP cases were eligible for the study. Among the groups, there were no significant differences in baseline demographic and clinical characteristics except the median number of prior uterine surgeries. Also, the groups did not significantly differ in their median fetal fraction. The fetal fraction did not discriminate any group when stratified according to the depth of placental invasion, i.e., no PAS, abnormally adherent, and abnormally invasive placenta. CONCLUSIONS: The maternal serum fraction of cell-free fetal DNA measured before 20 weeks of gestation is not predictive of PAS with or without concurrent PP or the depth of trophoblastic invasion.

Outcomes of pregnancies at high-risk for placenta accreta spectrum following negative diagnostic imaging.

OBJECTIVES: To assess the pretest and negative post-test probability for placenta accreta spectrum (PAS) in a group of patients with high-risk clinical factors. METHODS: We included patients with suspected and/or confirmed PAS at our institution over 8 years. Sonography performed by maternal-fetal medicine specialists, and selected patients underwent MRI. Imaging was considered positive if either sonography or MRI suggested PAS. Histopathology was the gold standard for diagnosis of PAS. We assessed the pretest and negative imaging-test probability, and resources required. RESULTS: We identified 82 high-risk patients with the following: (1) a history of ≥1 cesarean section and/or intrauterine gynecologic procedure and placenta previa in the index pregnancy; (2) a history of >3 cesarean deliveries and/or gynecologic procedures regardless of placental location; (3) prior PAS disorder, or retained placenta requiring manual extraction and/or curettage, complicated by postpartum hemorrhage; and (4) suspected cesarean section scar pregnancy. Histopathology confirmed PAS in 52 patients, with pretest probability of 63%. Imaging correctly identified 44/50 cases with PAS, and excluded this condition in 24/30 cases. Thus, the positive and negative post-test probability for PAS following negative imaging was 88 and 20%, respectively. Of the six patients with false-negative imaging, all had either surgical complications or required care beyond that for routine cesarean section. CONCLUSIONS: Although diagnostic imaging is sensitive, the negative posttest probability remains high in women with high pretest probability for PAS. Therefore, women at high risk for PAS should be managed in experienced centers by a multidisciplinary team even if imaging is negative.