OBJECTIVE: The present study was designed to determine the relation of umbilical venous blood flow (UmbBF) to fetal weight (FW) at different times in late pregnancy, and to assess fetal O-2 supply near term.STUDY DESIGN: In 46 pregnant women, UmbBF was calculated just before delivery using the product of flow velocity and the cross section of the umbilical vein determined by pulsed Doppler technique and measuring of the diameter of the vessel, respectively. Based on the gestational age at delivery ( range, 29-42 weeks), infants were divided into a preterm group ( PT; <= 36 weeks, n = 13) and a full-term group ( FT; <= 36 weeks, n = 33). Blood gas, pH, and hemoglobin analysis was performed in specimens of umbilical venous and arterial blood obtained after delivery.RESULTS: UmbBF was higher in FT infants ( 515 +/- 125 mL/min, mean +/- standard deviation) than in PT infants ( 423 +/- 120 mL/min; P <.05). This was associated with a larger increase in umbilical vein diameter: FT 8.8 +/- .7 mm, PT 8.1 +/- .6 mm ( P < .01). Partial pressure of O2 ( pO(2)) did not differ significantly between FT and PT; the correlation of pO(2) with gestational age showed a weak decrease (P < .05). Hemoglobin was elevated in FT ( P < .01), whereas O-2 content remained constant in PT and FT. The ratio UmbBF/FW was considerably reduced in FT [ 154 +/- 37 (mL/min)/kg], relative to PT [ 221 +/- 37 (mL/ min)/ kg; P <.001], and was accompanied by a marked reduction of O2 transport capacity: FT 17.6 +/- 6.7 and PT 26.6 +/- 9.2 ( mL/ min)/ kg ( P < .01).CONCLUSION: Due to the growth of the umbilical vein, UmbBF increases over the last weeks of gestation. The ratio UmbBF/FW is reduced in FT. Despite a constant O-2 content, the continuous weight-related decrease in UmbBF results in a reduction of the fetal O-2 transport capacity per unit that may contribute to an adverse intrauterine environment at the end of gestation, especially in postterm pregnancies.

Intrauterine uptake of vitamin B2 in preterm and full-term infants was examined. Factors of influence on vitamin supply were considered. Forty-four women and their infants were included in the study. Fetal vitamin uptake was calculated as arteriovenous concentration gradient in cord plasma times umbilical plasma flow. Concentration of vitamin B2 (free riboflavin and flavocoenzymes) was determined by high performance liquid chromatography of placental tissue and blood plasma (maternal vein, umbilical artery, umbilical vein). Flavocoenzymes were analyzed as flavin mononucleotide after acid hydrolysis of flavin adenine dinucleotide. Umbilical plasma flow was measured using pulsed Doppler sonography. Both free riboflavin and flavocoenzymes were transferred from the maternal plasma to the umbilical vein, but only free riboflavin was accumulated (∼1:4 for preterm and full-term infants, respectively). Flavocoenzyme concentration was higher in the umbilical vein than in the umbilical artery (p < 0.05). This indicated a median uptake of flavocoenzymes of 1.5 nmol/min-kg in preterm infants and 0.4 nmol/ min-kg in full-term infants (preterm versus full-term, p < 0.01). Fetal vitamin supply depended on umbilical plasma flow and on maternal vitamin status (the latter was shown only in full-term infants). No dependence on placental vitamin concentration was observed (p > 0.05). Concentration of free riboflavin was higher in umbilical artery than in umbilical vein (p < 0.05). This indicated a release of free riboflavin from fetal tissues independent of gestational age (0.4 nmol/murkg, preterm; 0.2 nmol/ min-kg, full-term; p > 0.05).