(885) Increases in routinely measured red cell indices during pregnancy are associated with obstetric complications

Pregnancy alters hematological indices, but intra-pregnancy changes in complete blood count (CBC) values have not been rigorously evaluated as markers of pregnancy health.

Study Design:

We retrospectively analyzed CBCs routinely measured at 7-14 and 26-29 weeks’ gestation to determine the association of rare changes in nine CBC indices (hematocrit, hemoglobin, red cell count, white cell count, platelets, mean red cell volume, mean red cell hemoglobin, red cell volume distribution width, and mean red cell hemoglobin concentration) with a composite outcome (hypertensive disorders of pregnancy, small for gestational age birthweight, preterm birth [both indicated and spontaneous]) and its individual components. Rare changes, defined as statistically uncommon changes in magnitude and direction, were identified in a discovery cohort of 29,162 pregnancies. Direction was chosen as the least frequent variation exceeding established non-pregnant biological variation, and magnitude as the threshold of change with the highest positive predictive value and significant OR (p < 9×10^-6 with Bonferroni correction). Identified associations were tested in an out-of-sample validation cohort of 50,603 pregnancies.

Results: In validation, increases in red cell indices between 7-14 and 26-29 weeks’ gestation were associated with the composite outcome with an OR [95% CI] of 1.49 [1.30, 1.70] for hematocrit, 1.57 [1.33, 1.86] for hemoglobin and 1.69 [1.48, 1.93] for red cell count. The strongest association with individual outcomes was observed for increases in hemoglobin ( >0.67 g/dL, OR 2.03 [1.58, 2.59]) or red cell count ( >0.07 106/mm3, OR 2.13 [1.74, 2.6]) and preterm birth (Table 1). These rare increases in hemoglobin and red cell count were observed on average 7 weeks before preterm birth; we did not observe a bias for detection of either spontaneous or indicated preterm birth.

Conclusion:

Deviations of routinely measured red blood cell indices from typical longitudinal trajectories during pregnancy may allow for early detection of obstetric complications.