CAP trial Blood pressure

The hypothesis that early pregnancy calcium supplementation modifies the pathogenesis of pre-eclampsia by having a direct effect on blood pressure.

This is the data used for a secondary analysis of a parallel arm, double-blind, randomised trial in South Africa, Zimbabwe and Argentina (PACTR201105000267371). Participants with previous pre-eclampsia/eclampsia received 500 mg calcium or placebo daily from enrolment pre-pregnancy until 20 weeks’ gestation. Both groups received unblinded calcium 1.5g daily after 20 weeks. We compared blood pressures between groups at 20 and 32 weeks’ gestation and investigated the effect of compliance on the two main trial outcomes.

We compared diastolic and systolic blood pressures between calcium and placebo groups at 20 weeks’ and at 32 weeks’ gestation. We also investigated the effect of compliance from the last visit before pregnancy to 20 weeks’ gestation (25%, 50%, 75%, and 80%) on blood pressure and the main trial results (pre-eclampsia, and ‘pregnancy loss or pre-eclampsia’).
The sample size for the current sub-study was opportunistic and based on the main study primary outcome (pre-eclampsia). Analyses were conducted by intention-to-treat (ITT), as well as at varying levels of compliance.

本研究的核心假说为：早孕阶段补钙可通过直接作用于血压水平，改变子痫前期（pre-eclampsia）的发病机制。
本数据集来自一项在南非、津巴布韦及阿根廷开展的平行组双盲随机试验（PACTR201105000267371）的二次分析。既往有子痫前期/子痫病史的受试者，自孕前入组至妊娠20周期间，每日服用500mg钙剂或安慰剂；两组受试者在妊娠20周后均需每日服用1.5g非盲钙剂。本研究比较了两组受试者在妊娠20周及32周时的血压水平，并分析了服药依从性对两项主要试验结局的影响。
我们进一步比较了妊娠20周及32周时，钙剂组与安慰剂组受试者的舒张压与收缩压水平；同时分析了自孕前末次随访至妊娠20周期间的服药依从性（分为25%、50%、75%、80%四个层级）对血压水平及两项主要试验结局（子痫前期、‘妊娠丢失或子痫前期’）的影响。
本次亚研究的样本量为机遇性选取，且基于主研究的主要结局指标（子痫前期）确定。分析过程采用意向性治疗（intention-to-treat, ITT）原则，同时也针对不同层级的服药依从性开展了相应分析。