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Oral Concurrent Session 2 - Clinical Obstetrics and Quality

Oral Concurrent Sessions

Oral Concurrent Session 2 - Clinical Obstetrics and Quality

(28) Investigating selection bias in research using placental pathology samples.

Thursday, January 30, 2025
3:45 PM – 4:00 PM  
Location: Aurora Ballroom B, Lobby Level
Objective: Increasing research interest has focused on placental pathology and pregnancy outcomes.  Clinically-requested pathology cases are often used for research due to convenience, which may lead to selection bias. We leveraged a large cohort of prospectively-collected placentas to compare prevalences of placental pathology in cases with and without a clinically-requested pathology exam (CPE) and to quantify potential selection bias.

Study Design:

All placentas were prospectively collected from participants in the Stress, Pregnancy, and Health (SPAH) study, including those with and without CPE. In all cases, placental pathology was categorized and graded in 4 major groups: acute inflammation (AI), chronic inflammation (CI), fetal vascular malperfusion (FVM) and maternal vascular malperfusion (MVM). We compared the distribution of placental pathology in cases with and without CPE. Odds ratios (OR) for preterm birth (PTB) and small for gestational age (SGA) infant were calculated in the whole SPAH cohort and compared with the CPE sub-cohort. Relative odds ratios (ROR) were used to quantify selection bias. Models were adjusted for sociodemographic and pregnancy characteristics.

Results:

575 placentas were collected and examined, 287 with CPE and 288 without CPE. The prevalence of AI, CI and FVM was similar among the 2 groups. However, the prevalence of MVM was significantly higher in CPE placentas, particularly for high grade MVM (15% vs 8%, p< 0.001). In adjusted models, high grade MVM was significantly associated with increased odds of PTB and SGA in the whole SPAH cohort and the CPE sub-cohort (PTB: SPAH OR=5.62, CPE OR=7.56; SGA: SPAH OR=8.13, CPE OR=8.25). RORs show a 30% overestimation of the association between MVM and PTB, and only a 2% overestimation in SGA when using a CPE sample.

Conclusion: MVM was the only placental pathology seen more frequently in the CPE sample. Research using a CPE only sample may overestimate associations, particularly for MVM and PTB. Because we quantified the selection bias, the RORs from our data can be used to adjust estimates in studies using retrospective CPE samples.