Postpartum imaging of renal structure following hypertensive and normotensive pregnancy

Abstract Background Pregnancy-related hypertension is linked to adverse kidney function during pregnancy and higher incidence of renal disease later in life. It is unknown at what timepoint early signs of structural maladaptation can be identified which predispose women to later disease. Purpose To compare structural changes in the kidneys 6 to 12 months postpartum in women with previous hypertensive and normotensive pregnancies. Methods 125 pregnant women (61 with preeclampsia, 33 with gestational hypertension and 31 with normotensive pregnancies), aged 18 and over, were followed up at 6 to 12 months postpartum. Anthropometric measurements, demographic characteristics, blood pressures and blood samples were collected during pregnancy and postpartum. Kidney structure was assessed postpartum using magnetic resonance imaging. Renal volumes, lengths, widths and depths were measured on 3D volumetric interpolated breath-hold examinations and corticomedullary differentiation was calculated using T1 mapping. Results At 6 to 12 months postpartum, total kidney volume (mean difference: -15.42, 95% confidence interval: [-30.84, -0.005], p = 0.0499) and right kidney volume (mean difference: -7.11, 95% confidence interval: [-14.13, -0.09], p = 0.046) were smaller in women who had preeclampsia compared to normotensive pregnancy, with no difference in total or right kidney volume between women who had a normotensive pregnancy or gestational hypertension. However, the gestational hypertension group had lower corticomedullary differentiation than both the normotensive (mean difference: 0.07, Z: 2.009, p = 0.067) and preeclamptic group (mean difference: 0.08, Z: 2.41, p = 0.024) 6 to 12 months postpartum. These differences were independent of blood pressure during pregnancy or postpartum. At birth, 14 women with preeclampsia (23.0%), 3 women with gestational hypertension (9.1%) and one normotensive woman (5.9%) had estimated glomerular filtration rates (eGFRs) of ≤90mL/min/1.73 m². By 6 to 12 months postpartum, one woman with gestational hypertension and 5 women with preeclampsia still had eGFRs ≤90mL/min/1.73m². Total kidney volume postpartum was significantly correlated with eGFRs at birth (ρ: 0.47, p < 0.001) but not postpartum. Conclusions Women who develop preeclampsia have smaller kidney volumes at postpartum follow up and their renal size is associated with the degree of subclinical renal impairment during pregnancy. In contrast, women who develop gestational hypertension predominantly have evidence of renal differences at the microstructural level. Further work is needed to understand whether subclinical changes in renal size are a clinically useful marker to identify women with hypertensive pregnancy who are predisposed to progressing to preeclampsia. In addition, longer term follow up will help establish links between these subclinical changes in renal volume and microstructure to longer term renal and cardiovascular risks after hypertensive pregnancy.Graphical Abstract