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Association between blunted glomerular hyperfiltration in pregnancy and severe maternal morbidity—a research letter


Background — Glomerular hyperfiltration is one physiological adaptation to pregnancy, marked by a decline in serum creatinine (SCr) concentration by 16 weeks’ gestation. It is not known whether blunted glomerular hyperfiltration leads to adverse maternal outcomes, including severe maternal morbidity (SMM).

Objective — To evaluate the association between blunted glomerular hyperfiltration and subsequent SMM or death.

Design — Population-based cohort study

Setting — Ontario, Canada, from 2008 to 2019.

Participants — Included were births among women who had ≥ 1 SCr measured as an outpatient within 10 weeks before conception (“preconception”), and again, at 110/7 to 206/7 weeks’ gestation (“in-pregnancy”). Excluded were women who died before birth, who had end-stage renal disease or kidney transplantation before conception, or whose pre-pregnancy SCr was 125 μmol/L.

Exposure — Net glomerular hyperfiltration defined as the preconception minus the in-pregnancy SCr.

Measures — The primary study outcome was SMM or death arising from 23 weeks’ gestation up to 42 days after the index birth.

Methods — Adjusted relative risks (aRRs) were calculated using Modified Poisson regression per 1-SD net blunting of glomerular hyperfiltration adjusting for important covariates.

Results — A total of 10,323 births met all inclusion criteria. The mean (SD) SCr was 61.7 (11.0) μmol/L preconception, 48.0 (9.2) μmol/L in-pregnancy, and the mean net difference 13.6 (8.2) μmol/L. Among these births, the adjusted RR of SMM or death from 23 weeks’ gestation up to 42 days post-partum was 1.16 (95% confidence interval 1.14-1.30) per 1-SD (8.2 μmol/L) net blunting of glomerular hyperfiltration.

Limitations — As SCr assessment is not a routine part of pregnancy care, its measurement could have been for a specific health condition thereby imparting selection bias.

Conclusions — Blunted glomerular hyperfiltration in pregnancy may identify some women at higher risk of SMM. Further prospective research is needed about the implications of glomerular hyperfiltration in early pregnancy.



Harel Z, Park AL, Ray JG. Can J Kidney Health Dis. 2021; 8:20543581211035221. Epub 2021 Oct 26.

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