UC San Diego

Abstract Introduction The majority of low placentation identified on first‐trimester transabdominal ultrasound resolves; however, whether this resolution is associated with adverse outcome remains poorly understood. This investigation aimed to determine whether patients with resolved first‐trimester low placentation had different delivery outcomes compared to patients who never had low placentation. Methods This is a retrospective cohort study of singleton pregnancies with low placentation, defined as low‐lying placenta or placenta covering the internal os, on first‐trimester transabdominal ultrasound between 12+0 weeks and 13+6 weeks, delivering at a single tertiary care center from January to December 2022. We compared outcomes stratified by first‐trimester low placentation that resolved by the second trimester, or those without low placentation at any point. The primary outcome was quantitative blood loss at delivery by volumetric measurement. Secondary outcomes included postpartum hemorrhage (PPH) defined as blood loss ≥1000 cc, unplanned cesarean delivery, preterm birth, 5‐min Apgar < 7, and composite maternal adverse outcomes including the use of atony device, retained products of conception, blood transfusion, peripartum hysterectomy, intensive care unit admission, or death. Results This cohort included 437 low placentation patients and 491 patients without low placentation. Resolved first‐trimester low placentation was associated with a significant increase in quantitative blood loss at delivery (405 ± 369 cc vs. 331 ± 253 cc, p  < 0.01) but no difference in incidence of PPH (6.4% vs. 4.7%, p  = 0.25). Resolved first‐trimester low placentation was also associated with increased tranexamic acid (TXA) administration (11.9% vs. 7.7%, p  = 0.03), blood transfusion (1.8% vs. 0.4%, p  = 0.04), and unplanned cesarean delivery (15.3% vs. 9.2%, p  < 0.01) without differences in the indications for unplanned cesarean delivery. In our multivariable regression, resolved first‐trimester low placentation remained associated with TXA administration (adjusted odds ratio [OR], 1.70; 95% confidence interval [CI], 1.07–2.70) and unplanned cesarean delivery (adjusted OR 1.73; 95% CI, 1.12–2.68). There were no associations with adverse neonatal outcomes or composite maternal outcome. Conclusion Resolved first‐trimester low placentation is not associated with clinically significant adverse outcomes. However, given changes in unplanned cesarean delivery rate, resolved low placentation may indicate altered uterine physiology. Future research would be valuable to better understand the relationship between resolved low placentation and unplanned cesarean deliveries.