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Association Between Blunted Glomerular Hyperfiltration in Pregnancy and Severe Maternal Morbidity-A Research Letter
Ziv Harel1,2, Alison L Park2, Joel G Ray2,3
1Division of Nephrology, St. Michael's Hospital, Toronto, ON, Canada.
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.
