Effects of ritodrine and fetal oxygenation after in utero fetal surgery in sheep.

Surgical procedures which involve the pregnant uterus are associated with preterm labor contractions in the postoperative period. Because uterine contractions decrease fetal oxygen tension, we investigated the effect of maternal ritodrine infusion on fetal oxygen consumption in catheterized fetal sheep 5 h postoperatively. During ritodrine infusion, uterine activity promptly abated, but the oxygen tension in the umbilical vein and descending aorta decreased. The arterial-venous oxygen content difference, the umbilical blood flow, and consequently, fetal oxygen consumption did not change significantly. We conclude that fetal oxygenation is not improved by eliminating uterine activity with maternal ritodrine infusion in the postoperative period.

Fetal oxygen uptake during uterine contractures.

During contractures there are decreases in fetal oxygen tension. In order to determine if there are concomitant changes in fetal oxygen consumption, we calculated the latter during contractures from measurements of the umbilical blood flow and venous arterial oxygen content differences across the umbilical circulation. There were decreases in both the umbilical venous (from 8.8 +/- 0.2 (SEM) to 8.5 +/- 0.2 ml.dl-1, P less than 0.01) and umbilical arterial (5.9 +/- 0.1 to 5.2 +/- 0.2 mg.dl-1, P less than 0.001) oxygen contents. The umbilical venous-arterial oxygen content difference increased from 2.9 +/- 0.1 to 3.3 +/- 0.2 ml.dl-1 (P less than 0.005). Umbilical blood flow was 194.3 +/- 4.5 ml.min-1 kg-1 during relaxation and was unchanged during contractures. Fetal oxygen uptake increased from 5.7 +/- 0.3 to 6.5 +/- 0.4 ml.min-1 kg-1 (P less than 0.005) during contractures. This observation is consistent with our previous speculation that there is increased muscular activity of tone associated with contractures.

Fetal cardiorespiratory changes during spontaneous prelabor uterine contractions in sheep.

Fetal cardiorespiratory changes during spontaneous prelabor uterine contractions (called contractures) were studied in 12 chronically catheterized fetal sheep at 120 to 143 days' gestation. During contractures the carcass blood flow increased significantly from 27 +/- 2 (SEM) to 32 +/- 3 ml/min/100 gm. There were no significant changes in combined ventricular output or in blood flow to the umbilical circulation, brain, heart, adrenal glands, gut, kidney, and lung. Fetal arterial blood pressure increased from 57 +/- 2 to 62 +/- 1 mm Hg (p less than 0.001) during contractions. There were no significant changes in fetal heart rate. In the fetal femoral artery during contractures the oxygen content decreased from 6.1 +/- 0.2 to 5.4 +/- 0.2 ml/dl of blood (p less than 0.001), and carbon dioxide tension increased significantly from 44 +/- 0.4 to 45 +/- 0.4 mm Hg (p less than 0.001). The pH did not change. The increase in carcass blood flow during contractures suggests that there was an increase in fetal skeletal muscular activity or tone. An increase in fetal skeletal muscle activity, together with a decrease in uterine blood flow could explain the small decrease in fetal oxygen content that occurs with each contracture. Fetal compression and/or changes from rapid eye movement to synchronized sleep or arousal observed during contractures are possible stimuli causing increased fetal skeletal muscle tone or activity. Since contractures periodically result in neuromuscular activity in the fetus in its protected fluid-filled environment, they may play a key role in fetal neuromuscular development by stimulating "exercising" in the fetus in utero.

Comparison of glucose polymer and glucose for screening and tolerance tests in pregnancy.

Forty-eight of 100 pregnant women received a 100-g (nonfasting) glucose screening test at about 28 weeks' gestation, followed by a 100-g glucose tolerance test. Another 52 received a 100-g (nonfasting) glucose polymer screening test followed by a 100-g glucose polymer tolerance test. Mean plasma glucose one hour after the glucose screening test was significantly lower than after the glucose polymer screening test. A further 178 women received a glucose polymer screening test and a glucose polymer tolerance test (230 in total). These women and the infants they delivered were studied to derive diagnostic criteria for the 100-g glucose polymer tolerance test by correlating maternal carbohydrate tolerance with indexes of neonatal metabolic performance, and to determine an adequate method of screening for carbohydrate intolerance of pregnancy (gestational diabetes). Diagnostic criteria similar to those of O'Sullivan and Mahan were also developed for the glucose polymer tolerance test. These values are up to 5% lower than those recommended by the National Diabetes Data Group (1979) for the 100-g glucose tolerance test.

Continuous measurement of oxygen consumption in fetal sheep.

A microcomputer-based system has been developed to measure oxygen consumption continuously in fetal sheep. The system includes an umbilical artery electromagnetic blood flow transducer and two fiberoptic catheter oximeters for measuring umbilical artery and vein oxyhemoglobin saturation in vivo. The electrical signals from these instruments are digitized and sampled by a microcomputer. Fetal oxygen consumption is calculated from the Fick principle by use of the digitized signals and hemoglobin concentrations. The latter is measured intermittently and updated if necessary. System validation required that artifacts in oxyhemoglobin recordings could be avoided and that the catheter readings agreed with values from intermittent samples. Continuous heparin infusion and careful catheter placement facilitated attainment of these requirements. The system can be used to obtain continuous recordings of fetal oxygen consumption during rapidly occurring physiologic events.

Effects of beta-adrenergic blockade on blood flow distribution during hypoxaemia in fetal sheep.

Hypoxaemia in fetal sheep causes a decrease in vascular resistance of the heart, brain and adrenal gland which results in increased blood flow to these organs. Placental blood flow is maintained. To investigate whether increased beta-adrenergic activity during hypoxaemia is involved in these changes, the effects of propranolol on organ blood flows (using the microsphere method) and other cardiovascular variables were studied during fetal hypoxaemia (50% reduction of fetal haemoglobin saturation) in 5 chronically catheterized fetal sheep at 126 to 130 days of gestation. Beta-blockade during hypoxaemia caused a fetal bradycardia and a 30% drop in cardiac output. Placental and myocardial blood flows fell by 39% and 37% respectively. Total peripheral resistance increased by 35% mainly due to increased fetal placental vascular resistance. Heart and lung vascular resistances increased following propranolol. In 3 similarly catheterized animals, propranolol administered in the absence of hypoxaemia led to a 9% drop in cardiac output and placental blood flow but no redistribution of blood flow to fetal organs. It is concluded that the increased beta-adrenergic activity associated with fetal hypoxaemia limits the negative chronotropic effects of concomitantly increased vagal activity, maintains placental blood flow through its inotropic and chronotropic activity as well as by maintenance of placental vasodilatation and may be one of several factors which increase myocardial blood flow during hypoxaemia.

Comparison of glucose and a glucose polymer for testing oral carbohydrate tolerance in pregnancy.

Forty-six pregnant patients with potential diabetes were studied to compare the use of glucose and a glucose polymer for carbohydrate tolerance testing. The first 26 patients had a glucose tolerance test and a glucose polymer tolerance test in randomized order an average of one week apart. The mean tolerance curves and insulin curves were similar for both agents. Patients preferred glucose polymer to glucose because of a lower incidence of associated nausea. A second group of 20 patients was randomly divided so that patients had two glucose tolerance tests or two glucose polymer tolerance tests an average of one week apart. Comparison of the variability and correlation of the incremental areas under the paired tolerance curves showed that the reproducibility of the glucose polymer tolerance test exceeded that of the glucose tolerance test.

Fructosamine in diabetic pregnancy.

Fructosamine, an indicator of glycosylated serum protein, was measured in 79 non-diabetic pregnant women and 20 women with gestational diabetes. The test provided a clear discrimination between groups; it detected 17 (85%) of the women with gestational diabetes and gave only 4 (5%) false-positive results. 19 women with established diabetes before pregnancy had very high levels. Maternal fructosamine at 29 weeks' gestation correlated significantly with both fasting blood glucose levels at the time and birthweight ratio. Levels of fructosamine in cord blood were significantly higher in gestational diabetic than in normal pregnancies, suggesting a possible additional role for fructosamine in retrospectively detecting the hyperglycaemic fetus. Fructosamine estimation is fully automated and may provide a simple, inexpensive means to screen for diabetes in pregnancy.

Molar pregnancy of hyperthyroidism.

A report on a patient with clinical hyperthyroidism associated with hydatidiform mole is presented. Some biochemical characteristics of the thyroid stimulator isolated from the tumour are discussed.