Wiegel RE, Jan Danser AH, Steegers-Theunissen RPM, et al. - In this two observational prospective cohort studies, researchers sought to examine maternal renin-angiotensin-aldosterone-system (RAAS) determinants in early pregnancy. Pregnancies (n = 277) have been stratified by CL number and in-vitro fertilization (IVF) protocol: 0 CL (programmed cycle frozen embryo transfer [FET], n = 28), 1 CL (natural cycle FET, n = 41 and spontaneous conceptions, n = 139) and >1 CL (ovarian stimulation and fresh embryo transfer, n = 69). According to findings, prorenin and renin were lower in the absence of a CL at all-time points compared with 1 CL, whereas prorenin, renin and aldosterone were higher in the presence of >1 CL vs 1 CL. CL number, IVF protocol, BMI, PCOS, and AMH affect maternal RAAS activation during early pregnancy and can therefore lead to complications in pregnancy.