In vivo transplacental transport and metabolism in small and appropriate for gestational age fetuses

The results of this thesis include the following:-.; 54 fetuses were studied, of which 33 were appropriate for gestational age (AGA) and 21 SGA. The mean birthweight of the AGA fetuses (3227 471 g) was significantly higher than that of SGA fetuses (2361 245g).; The overall mean umbilical vein blood flow was 86 24 ml. kg.-1 min.-1. Blood flow was significantly lower in SGA fetuses (66 23 ml. kg.-1 min.-1) compared with AGA fetuses (90 18 ml. kg.-1 min.-1).; Mannitol clearance across the placenta decreased as maternal mannitol concentration increased indicating saturation of a transfer process. Mannitol transfer across the placenta was therefore thought to be carrier mediated rather than passive as had been previously thought and implicitly cannot be used as a good extracellular marker. The mean clearance of mannitol in SGA pregnancies (5.6 2.1 ml. min.-1) was significantly lower than in AGA pregnancies (12.8 1.6 ml. kg.-1 min.-1).; L-leucine transport across the placenta was significantly lower in the SGA fetuses.; Glycine transport and fetal uptake were significantly lower in the SGA group. In addition, neonatal glycine levels were significantly lower in the AGA group.;The transport of D-and L-leucine and glycine across the placenta is defective in SGA pregnancies. In addition, fetal uptake of these amino acids is significantly reduced. D-leucine is actively transported across the placenta and the same transporter may be involved in carrying D- and L-leucine. Glycine metabolism in the SGA neonates is significantly slower than that of AGA neonates.