The somatotropic axis plays an important role for embryonic growth and development. However, less is known about the effect of early pregnancy (embryo signaling) on the maternal GH-IGF-system. The aim was to investigate endocrine endpoints of the somatotropic axis in pregnant vs. non-pregnant dairy heifers until d18 of pregnancy. Blood samples of Holstein Friesian heifers (n=30) were taken on d0 (day of ovulation, defined by ultrasonography) and days 7, 14, 16 and 18 in repeated consecutive pregnant (p) and non-pregnant (np) periods. Additionally, liver biopsies were taken on d18. Heifers received artificial insemination or embryo transfer and pregnancy was verified either on d18 (P4 >2.0 and successful recovery of a conceptus [n=12]) or retrospectively on d42 (detection of embryonic heart beat [n=21]). The cows were defined as non-pregnant on d18 if P4 was <2.0 and no conceptus was recovered (n=29). Out of 62 periods, 38 were selected to build 19 pairs (np-p or p-np) for analysis by ANOVA as repeated measurements. Concentrations of progesterone, estrogens, GH, IGF-I and IGF-II were measured by the use of validated immunoassays. The blood concentration of IGFBP-2 to -4 at d0, d14 and d18 was determined using a quantitative western ligand blot. Hepatic mRNA expression of GHR, IGF-I, IGF-II, IGFBP-2 to -4 was detected by qPCR. At d18 the IGF-I [ng/ml] serum concentration tended to be lower in pregnant compared to non-pregnant heifers (284.9±82.6 vs. 321.8±81.6; P=0.082). In both groups IGF-I decreased from d0 to d16 (P<0.001) and increased towards d18 in pregnant (P<0.05) and in non-pregnant (P<0.001) heifers. The IGF-II [ng/ml] concentrations between pregnant and non-pregnant were comparable and increased in both groups between d0 and d14 (P<0.05). At d18, the IGFBP-4 [µg/ml] blood concentration was lower in pregnant (0.44±0.26) compared to non-pregnant heifers (0.75±0.36) (P=0.012). In liver biopsies IGFBP-3 expression tended to be lower in pregnant compared to non-pregnant cows (P<0.1). The reduced maternal serum IGFBP-4 may be due to enhanced proteolytic activity and as IGFBP-4 can inhibit IGF-I action, these data propose, that it may also lead to increased free IGF-I levels, potentially useful for local action at the cellular level e.g. in the endometrium of pregnant individuals.