Associations between abnormal placental and fetal development after in vitro embryo manipulations have been suggested to play a key role in the occurrence of high birth weights. This study was designed to investigate bovine conceptus development in in vivo- (controls) and in vitro-produced (IVP) concepti and newborn calves, and its association with specific placental proteins usually present in maternal, fetal and neonatal plasma and fetal (amniotic and allantoic) fluids. Females were superovulated to obtain control embryos, whereas IVP embryos were derived from established in vitro embryo production procedures (Bertolini et al., 2002 Theriogenology 58,973). Pregnant animals from each group were slaughtered on Days 90 and 180 of gestation (n = 4 control, n = 5 IVP pregnancies/day), or allowed to develop to term (n = 6/group). Conceptus and neonatal physical traits were recorded after slaughter or delivery (Bertolini et al., 2001 Theriogenology 55, 347; 2002 57, 361; 2002 58, 973). Maternal and fetal plasma and fluids were sampled after slaughter; maternal blood was sampled weekly from Day 30 of pregnancy to term. Neonatal blood samples were collected at 10 min, and at 1, 6, 12 and 24 h after birth. Bovine placental lactogen (bPL) and pregnancy-specific protein B (bPSPB) concentrations were determined in plasma and fluid samples, according to Wallace (1993 Dom. Anim. Endocrinol. 10, 67) for bPL, and by a commercial service for bPSPB (BioTracking, Moscow, ID, USA.). Data were compared by Proc GLM of SAS and Pearson’s correlation test (SAS Institute, Cary, NC, USA.). No major physical differences in conceptus traits were observed between groups on Day 90, but concentrations of bPL and bPSPB were higher in fetal plasma (8.1 ± 0.5 v. 10.7 ± 0.5 ng mL^-1 for bPL, and 4.4 ± 8.2 v. 32.5 ± 5.8 ng mL^-1 for bPSPB) and allantoic fluid (bPL only; 3.6 ± 1.1 v. 7.8 ± 1.0 ng mL^-1) of IVP concepti (P < 0.05). Day-180 IVP pregnancies displayed larger uterine and conceptus traits (P < 0.05), and bPSPB concentrations were 2.9-fold lower (84.3 ± 22.4 v. 20.5 ± 22.4 ng mL^-1) in the allantoic fluid (P < 0.05) of IVP pregnancies, for a 2- to 3-fold larger allantoic fluid volume than controls (P < 0.07). Concentrations of bPL in fetal plasma and fluids were higher than in maternal plasma, but no differences in bPSPB concentrations were observed across fluid types. Newborn IVP calves and fetal membranes were larger, displaying 3- to 4-fold higher concentrations of plasma bPL (P < 0.05) and bPSPB (P < 0.08) than controls (10 and 60 min after birth) and maternal plasma (at delivery). Maternal concentrations of bPL in IVP pregnancies were lower than controls during the last 8 weeks of gestation (P < 0.05), to become similar as parturition approached. Generally, concentrations of bPL and bPSPB in plasma were correlated with physical traits (0.750 > r > 0.958, P < 0.001) and with one another in plasma and fluids (0.715 > r > 0.938, P < 0.001). Our results indicated that differential patterns of secretion of bPL and bPSPB into the maternal and fetal systems occurred at distinct stages of gestation, which were associated with altered conceptus development after in vitro embryo manipulations, indirectly demonstrating deviations in placental function in IVP pregnancies.