Revisiting Severe Maternal Morbidity Recurrence: Selection Bias and the Implications for Risk Estimation Across Pregnancies.

Authors

Rashida S Smith-Webb, Martha M Werler, Samantha E Parker, Jennifer Weuve, Collette N Ncube

Published in

Epidemiology (Cambridge, Mass.). Jul 21, 2026. Epub Jul 21, 2026.

Abstract

Selective attrition may bias estimates of severe maternal morbidity (SMM) recurrence; however, no study has quantified this bias. Using inverse probability (IP) of continuation weights, we examined bias from selective attrition for the effect of SMM (versus no SMM) at the index delivery on the risk of SMM at the second delivery.
Using data from the Pregnancy to Early Life Longitudinal Data System in Massachusetts, we identified nulliparous individuals aged 12-55 years with singleton, in-hospital deliveries, from 1998-2021. We followed individuals from their index delivery (N = 571,862) until a second hospital delivery, competing event, loss to follow-up, or administrative end of the study (12/31/2021). We applied logistic regression to model attrition from competing events and loss to follow-up and computed IP of continuation weights. Risk differences (RD, per 10,000 in-hospital deliveries) and risk ratios (RR), along with 95% confidence intervals (CIs) were estimated from modified Poisson regression models with identity-link and log-link functions, respectively.
In unweighted, multivariable-adjusted analyses, SMM at the index delivery was associated with an increased risk of SMM at the second delivery (RD: 506.1 [95% CI: 379.6, 632.7]; RR: 5.39 [4.37, 6.65]). Weighting to account for attrition resulted in a slight increase (RD: 510.6 [383.0, 638.0]; RR: 5.42 [4.39, 6.68]). Unweighted estimates were biased downward (<1%). Black individuals had the highest rates of SMM recurrence (RD: 1076.6 [624.2, 1528.9]; RR: 6.24 [4.27, 9.13]).
Selective attrition had minimal influence on estimates of SMM recurrence in this setting.

PMID:
42479546
Bibliographic data and abstract were imported from PubMed on 22 Jul 2026.

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