In adult pregnancy, the gravid uterus receives a high priority status for nutrient partitioning. A shift in this hierarchy in favor of maternal tissues, as seen in adolescent pregnancy, compromises placental growth and fetal development. This situation occurs during gestation in growing heifers and lactating cows, as a high priority status of respectively maternal tissue growth and lactation is then observed. To assess the effect of dam lactation and growth on placental and fetal development, placentas of 49 multiparous (MP) Holstein Friesian (HF) cows and 43 growing heifers [27 HF and 16 Belgian Blue (BB)] were compared with afterbirths of 27 non-growing, nonlactating MPBB cows. Placentas were weighed and cotyledons were removed, after which their surface was calculated by the formula area(ellips) = πab; with a = half of major diameter and b = half of minor diameter. Placental efficiency (PE) was assessed by the calf weight:cotyledonary surface ratio. Analysis of variance was used to compare placental weight and cotyledonary surface, differences in cotyledon number and PE were assessed by the Kruskal-Wallis test. Placentas of MPBB dams weighed 5.9 ± 1.79 kg with a cotyledonary surface of 0.53 ± 0.110 m². Placentas of MPHF dams were 0.9 kg lighter (P < 0.01) but tended to have a larger total cotyledonary surface (0.58 ± 0.106 m², P = 0.05). Placentas of heifers were smaller (4.7 ± 1.34 kg and 0.48 ± 0.085 m², P < 0.05), without significant breed effect. The number of cotyledons in MPBB placentas (91 ± 27.2) was lower than in placentas of heifers and MPHF (respectively 114 ± 29.0 and 115 ± 28.2, P < 0.05). In addition, MPHF dams had a greater proportion of small (<60 cm²) cotyledons; as mentioned in nutrient-restricted ewes. MPBB cows had the highest PE of 107 ± 25.1 kg/m², compared with 74 ± 13.5 kg/m² in MPHF dams (P < 0.01). BB and HF heifers had a similar PE of 96 ± 23.0 and 84 ± 18.0 kg/m² respectively. These preliminary findings suggest maternal growth and lactation during gestation to have a similar nutrient restrictive effect on placental development, which may result in a lower PE. This could be, at least partly, responsible for the differences in size of the offspring. Further research is necessary to assess the influence on organ development and future health of the calves.