Page 29 - Pro-active Management of Women’s Health after Cardiometabolic Complicated Pregnancies

Hypertension was defined as the use of anti-hypertensive drugs or a blood pressure ≥ 140/90 mmHg. Proteinuria was defined as ≥ 0.3 grams/day urinary protein loss. For both conditions separately the first visit of measured resolution was identified. Because resolution obviously occurred somewhere between visits, actual time of resolution was analyzed as interval censored. If no visit of resolution could be identified and follow-up data was incomplete, women were considered lost-to-follow-up. Turnbull’s extension of the Kaplan-Meier procedure to interval-censored data91 was then used to calculate resolution- curves with 95% confidence bands (SAS 9.1.3, SAS Institute Inc., Cary, NC, USA). The women that were lost-to-follow-up were right-censored in the analysis under the assumption of independent censoring from the time of resolution. This means that after the last known visit, the proportion of right-censored women who showed resolution was equal to the proportion of women with complete follow-up who showed resolution at a specific time.
Hospital files were searched to collect clinical features of preeclampsia. They included maximal systolic and diastolic blood pressure during admission, maximal level of proteinuria during admission, gestational age at onset of preeclampsia and the time interval between diagnosis and delivery. To analyze the correlation between these covariates and the rate of resolution, we used an accelerated failure time (AFT) model with flexible error distribution allowing for interval censoring as described elsewhere92 (smoothSurv 0.3-12 R 2.7.1, Komarek). This model is not restricted to assume a specific distribution for the error like Gaussian or extreme value distribution, but allows a smooth error distribution resulting from the penalized normal mixture.
This study was approved by the Institutional Research Board of the Erasmus University Medical Center (trail number MEC-2009-169).
2.1 Resolution of hypertension and proteinuria| 27