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A Canadian matched cohort study found that pregnancies after kidney donation were associated with higher rates of hospitalization for gestational hypertension, preeclampsia or eclampsia, and small-for-gestational-age births. The absolute rates remained relatively low, and most secondary outcomes showed no clear difference; the researchers say the birth-size finding needs confirmation.
A Canadian study found that women who had donated a kidney were more likely than matched nondonors to be hospitalized with gestational hypertension, preeclampsia or eclampsia during a later pregnancy, although the complications remained uncommon overall. The research, presented at the American Society of Nephrology Kidney Week meeting and published in JAMA on October 22, also linked donation with more small-for-gestational-age births, a finding the lead researcher said needs confirmation.
The study included 385 pregnancies among 252 kidney donors and 1,540 pregnancies among 1,535 nondonors, drawn from administrative health data in three Canadian provinces. Researchers matched pregnancies on factors including maternal age, delivery date, parity, time between cohort entry and delivery, and income quintile. The pregnancies were singleton births at 20 weeks’ gestation or later.
The primary outcome was hospitalization with a diagnosis of gestational hypertension, preeclampsia or eclampsia. It occurred in 11.9% of donor pregnancies, compared with 8.3% of matched nondonor pregnancies (risk ratio 1.51; 95% confidence interval 1.10-2.08). Small-for-gestational-age births—defined as birth weight below the 10th percentile—occurred in 13.8% of donor pregnancies and 7.9% of nondonor pregnancies (risk ratio 1.86; 95% CI 1.37-2.52).
The authors reported no clear differences across 11 other secondary outcomes, including cesarean delivery, gestational diabetes, preterm birth or low birth weight, neonatal intensive care admission, stillbirth and neonatal death. Fewer than 2% of pregnancies in either group had the primary outcome first recorded before 34 weeks, according to lead author Amit X. Garg, MD, PhD, of London Health Sciences Centre in Ontario.
Pregnancy Counseling After Donation
The findings add evidence relevant to people weighing living kidney donation before a possible future pregnancy. About 65% of living kidney donors are women, and roughly 75% are of childbearing age at donation, the report said. A higher relative risk can matter in counseling even when the overall outcome is uncommon: in this study, most donor pregnancies did not have the primary complication.
Garg told MedPage Today that donor candidates who may become pregnant should be counseled about a potentially modestly higher chance of gestational hypertension or preeclampsia. He also said people who become pregnant after donation should have access to appropriate prenatal care, with attention to blood pressure and other signs of hypertensive disorders. The results do not establish that donation itself caused the outcomes, and they do not mean that a future desire for pregnancy should automatically rule out donation.
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How the Canadian Study Fits
The study’s primary finding is consistent with prior research that informed 2017 international guidelines recommending that clinical teams discuss potential gestational hypertensive disorders with kidney donor candidates. Pregnancy increases demands on the kidneys, including renal blood flow and filtration. The authors also cited experimental research in mice without one kidney that found changes in kidney adaptation and placental function; this provides biological context, not proof of the mechanism in human pregnancies.
The higher rate of small-for-gestational-age births was less expected, Garg said, and it arose among several secondary outcomes examined. The authors said it therefore needs confirmation in other studies. Their analysis also found a larger risk ratio for the primary outcome among donors aged 35 or older at delivery: 14.3% versus 7.6% (risk ratio 1.99; 95% CI 1.18-3.33). Among those under 35, the rates were 10.7% and 8.7% (risk ratio 1.41; 95% CI 0.93-2.15). The study does not establish that age changes the effect of donation.
“Donor candidates who may become pregnant should be counseled that donation may be associated with a modestly higher chance of developing gestational hypertension or preeclampsia.”
— Amit X. Garg, MD, PhD, lead author, speaking to MedPage Today
Limits on Risk Estimates
The study was observational, so it shows an association, not proof of cause. The authors noted that some donors are related to the people receiving their kidneys; shared genetic factors could contribute to kidney or pregnancy risks. The administrative data also lacked information on maternal body mass index, blood pressure measurements and medication use during pregnancy, leaving room for residual confounding.
The birth-size result is also less settled than the primary finding because it was one of several secondary outcomes. The study cannot determine whether the differences apply equally to all donor candidates or explain the biological pathway behind them. Its population-based records covered three Canadian provinces, and the reported findings do not resolve how risks may vary in other populations or care settings.
What Researchers Will Check
The next step is confirmation in further studies, particularly for the small-for-gestational-age finding. The published report does not specify a planned follow-up study or a date for new results. In the meantime, the authors’ findings support discussing pregnancy-related risks with potential donors and providing appropriate prenatal monitoring to those who later become pregnant. Decisions about donation and pregnancy care should be discussed with qualified clinicians familiar with the individual’s health history.
Key Questions
The study’s composite outcome occurred in 11.9% of kidney-donor pregnancies and 8.3% of matched nondonor pregnancies. It included hospitalization with gestational hypertension, preeclampsia or eclampsia; the comparison shows an association, not proof that donation caused the difference.
Did the study find more small-for-gestational-age births after donation?
Yes. The rate was 13.8% among donor pregnancies and 7.9% among nondonor pregnancies. The lead author said this secondary finding needs confirmation in other studies.
Does the study mean someone planning a pregnancy should not donate a kidney?
No. Garg said a desire for future pregnancy should not, by itself, exclude someone from living donation. The findings are relevant to counseling and should be considered alongside the benefits and risks for the donor and recipient.
Were most pregnancies after kidney donation complicated?
No. The primary outcome occurred in 11.9% of donor pregnancies, meaning most did not have a recorded hospitalization for the specified hypertensive disorders. The report also said fewer than 2% in either group had that outcome first recorded before 34 weeks.
What are the main limitations of the research?
The observational study cannot establish cause and effect. The researchers also lacked data on factors such as body mass index, pregnancy blood pressure measurements and medication use, and noted possible genetic similarities between some donors and recipients.
Source: rss
