Relationships between reproductive hormones and maternal pregnancy physiology in women conceiving with or without in vitro fertilization

We evaluated maternal pregnancy adaptations and their relationships with circulating hormones in women who conceived with or without in vitro fertilization (IVF). Pregnancies were grouped by corpus luteum (CL) number: 1 CL with physiological plasma relaxin concentration (P RLN ; spontaneous pregnancies); 0 CL without circulating RLN (programmed cycles); >1 CL with elevated P RLN (ovarian stimulation). Major findings were that declines in plasma osmolality (P osm ) and plasma sodium concentration ([Formula: see text]) were comparable in the 1 CL and 0 CL cohorts, correlated with plasma estradiol and progesterone concentrations but not P RLN ; gestational declines in plasma uric acid (UA) concentration (P UA ) were attenuated after IVF, especially programmed cycles, partly because of subdued increases of renal UA clearance; and P RLN and cardiac output (CO) were inversely correlated when plasma estradiol concentration was below ∼2.5 ng/mL but positively correlated above ∼2.5 ng/mL. Unexpectedly, P RLN and plasma sFLT1 (P sFLT1 ) were directly correlated. Although P sFLT1 and CO were not significantly associated, CO was positively correlated with plasma placental growth factor (PLGF) concentration after the first trimester, particularly in women who conceived with 0 CL. Major conclusions are that 1) circulating RLN was unnecessary for gestational falls in P osm and [Formula: see text]; 2) P RLN and CO were inversely correlated during early gestation, suggesting that P RLN in the lower range may have contributed to systemic vasodilation, whereas at higher P RLN RLN influence became self-limiting; 3) evidence for cooperativity between RLN and estradiol on gestational changes in CO was observed; and 4) after the first trimester in women who conceived without a CL, plasma PLGF concentration was associated with recovery of CO, which was impaired during the first trimester in this cohort.