Decreased urine production in the near-term fetal lamb after maternal ethanol infusion

Intravenous infusion of 1 gm ethanol/kg maternal body weight over 1 hour to three conscious catheterized near-term pregnant ewes decreased fetal urine production for 3 hours (overall decrease of 54% from control). This effect in the near-term fetus is opposite to the ethanol-induced diuresis that occurs in adults.     

Braxton Hicks' contractions and motor behavior in the near-term human fetus

The transient relationship between Braxton Hicks' contractions and fetal motor behavior was studied in 14 healthy nulliparous women near term. Two-hour recordings of fetal heart rate and uterine contractions and of real-time scanning for fetal body movements, breathing, and eye movements were made. The recordings were divided into state 1F and non-state 1F. Braxton Hicks' contractions were not influenced by fetal behavioral states and state changes were not related to these contractions. Fetal body movements did not stimulate contractions, but contractions coincided with a specific clustering of body movements during the ascending part of contractions. Breathing was clustered during the descending part of short-lasting contractions but decreased gradually during the long-lasting ones. Heart rate variation was increased during contractions.     

Fetal heart rate patterns in the small-for-gestational-age human fetus

A total of 24 pregnant women with growth-retarded fetuses were studied to examine the distribution of fetal heart rate accelerations between 30 and 40 weeks' gestation, as compared with those of fetuses of normal growth that were matched for gestational age and length of fetal heart rate tracings. Growth-retarded fetuses had significantly lower PO2 levels in the umbilical artery at birth (3 mm Hg less) than did healthy fetuses (p less than 0.05), but without metabolic acidosis. There was a larger proportion of small amplitude (less than 10 beats/min) and a smaller proportion of large amplitude (greater than 20 beats/min) fetal heart rate accelerations in the small-for-gestational-age fetuses than in the fetuses of normal growth. Although the number of accelerations was significantly reduced (50% less) in growth-retarded fetuses compared with healthy fetuses, there was no significant difference in the mean basal fetal heart rate and the mean number of decelerations between the two groups. Currently used definition of an acceleration as greater than or equal to 15 beats/min for greater than or equal to 15 seconds was applicable only in fetuses of normal growth. We hypothesized that a decrease in absolute acceleration frequency might be a useful index to detect the chronically hypoxemic fetus before severe metabolic acidosis and irreversible damage occurred.     

Nitric oxide modulates angiotensin II-induced drinking behavior in the near-term ovine fetus

OBJECTIVE: Human and ovine fetuses demonstrate an enhanced rate of spontaneous and angiotensin II-stimulated swallowing. Angiotensin II and nitric oxide synthase have been localized to thirst centers in the brain. This study was performed to determine whether central nitric oxide contributes to the regulation of angiotensin II-induced fetal swallowing. STUDY DESIGN: Six pregnant ewes with near-term singleton fetuses were chronically prepared with fetal vascular and lateral ventricle catheters and electrocorticogram and esophageal electromyogram electrodes. After a 2-hour control period, fetuses were administered serial lateral ventricle injections (1 mL) of angiotensin II (3.2 microg; time, 2 hours) and N omega-nitro-L -arginine methyl ester (3 mg; time, 3 hours) and a repeat angiotensin II injection (3.2 microg; time, 5 hours). All fetuses received an additional control study of lateral ventricle injections of artificial cerebrospinal fluid on a previous day. RESULTS: Angiotensin II injection significantly increased mean +/- SEM fetal swallowing (0.9 +/- 0.1 to 2.7 +/- 0.4 swallows/min). N omega-nitro-L -arginine methyl ester significantly decreased fetal swallowing to below the basal rate (0.4 +/- 0.1 swallows/min), and swallowing did not increase with the second angiotensin II dose (in the presence of nitric oxide blockade). CONCLUSIONS: These results demonstrate that inhibition of central nitric oxide suppresses fetal swallowing behavior in response to central angiotensin II. We speculate that tonic nitric oxide facilitates angiotensin II swallowing stimulation by maintenance of glutamate activation of hypothalamic N -methyl-D -aspartate receptors.     

Effect of oral sucrose on ingestive behavior in the near-term ovine fetus

BACKGROUND: Dipsogen-mediated ingestion matures acutely in late gestation because the preterm fetus may demonstrate absent responses to putative dipsogens. Although central appetite-mediated ingestive behavior is functional near term, it is unknown whether peripheral mechanisms for stimulation of appetite also are functional. In the adult, sweet taste stimulates and potentiates ingestive behavior. We sought to determine whether oropharyngeal sucrose exposure stimulates ingestive behavior in the near-term ovine fetus. STUDY DESIGN: Time-dated pregnant ewes with near-term singleton fetuses (n = 6) were chronically prepared with fetal vascular and sublingual catheters and esophageal electromyogram electrodes and studied at 129 +/- 1 days of gestation. After an initial 2-hour baseline period, successive solutions of distilled water and 2.5%, 10%, and 40% sucrose were infused sublingually (0.25 mL/min), each for 2 hours. Maternal and fetal arterial blood samples were drawn at timed intervals. RESULTS: During the basal period, fetal swallowing averaged 0.9 +/- 0.1 swallows per minute. Swallowing did not change in response to distilled water (0.9 +/- 0.2 swallows per minute) but significantly increased after sublingual infusion of 2.5% sucrose (1.3 +/- 0.1 swallows per minute), 10% sucrose (1.8 +/- 0.1 swallows per minute), and 40% sucrose (1.3 +/- 0.1 swallows per minute, P =.001). There were no significant changes in other fetal or maternal parameters. CONCLUSIONS: The stimulation of fetal swallowing in response to sublingual sucrose infusion suggests that taste-mediated ingestive behavior is functional in the near-term fetus and that both central and systemic appetite mechanisms are intact near term. Fetal swallowing increased in response to an increase in sucrose concentration to peak at 10% and then decreased with further rises in concentration, possibly mediated by aversive fetal reaction to a high-intensity sucrose concentration.     

Ovine fetal urine production following maternal intravenous furosemide administration

The response of the ovine fetus to maternal furosemide administration was studied in six chronically catheterized fetal lamb preparations. These studies indicate that in the chronic sheep model maternally administered diuretics do not augment fetal urine production. Additionally, passage of the drug from the maternal intravascular compartment to the fetal intravascular compartment could not be demonstrated. It is suggested that on the basis of these data, the results of the "Lasix challenge test" should be interpreted with caution when they are used to evaluate human fetal renal function.     

Neuropeptide Y administered into cerebral ventricles stimulates sucrose ingestion in the near-term ovine fetus

OBJECTIVE: In adults, nutrient intake is controlled by opposing actions of appetite stimulants (eg, neuropeptide Y [NPY]) and suppressors (eg, leptin). Because NPY may exert a preferential role in mediating adult carbohydrate intake, we sought to determine the effect of central NPY on near-term fetal carbohydrate ingestion. STUDY DESIGN: Five pregnant ewes and fetuses were prepared with fetal vascular, sublingual, and intracerebroventricular catheters, electrocorticogram, and esophageal electromyogram electrodes and studied at 131+/-2 days' gestation. After a 2-hour baseline period, 10% sucrose was infused sublingually for the duration of the study. At 4 hours' time, NPY was injected into the fetal cerebral ventricles and fetal swallowing monitored for an additional 6 hours. RESULTS: During the basal period, mean (+/-SEM) swallowing averaged 0.8+/-0.1 swallows per minute. Fetal swallowing increased significantly in response to sublingual sucrose (1.3+/-0.1 swallows/min, P=.001), and further significantly increased at 4 to 6 hours after NPY injection into the cerebral ventricles (1.8+/-0.3, P=.001). CONCLUSION: These results indicate central NPY stimulation of fetal ingestion beyond that resulting from sublingual 10% sucrose. The in utero development of NPY-induced ingestive behavior may be in preparation for high neonatal caloric intake.     

Alterations in maternal corticosteroid levels influence fetal urine and lung liquid production

OBJECTIVE: This study was designed to test the hypotheses that disruption of maternal adrenal secretion in late pregnancy requires fetal adaptations in order to maintain fetal blood volume and fetal viability. METHODS: Pregnant ewes were adrenalectomized at approximately 112 days, and cortisol and aldosterone were replaced to either normal pregnant levels (with 1 mg/kg per day of cortisol and 3 microg/kg per day of aldosterone) or normal nonpregnant levels of aldosterone or cortisol (0.5 mg/kg per day of cortisol or 1.5 microg/kg per day of aldosterone). RESULTS: Fetal blood volume, blood pressure, lung liquid production, urine production, free water clearance, and glomerular filtration rate were measured at 130 days. In a separate group, fetal organ blood flow was measured. Fetal blood volume was not significantly decreased by disruption of maternal corticosteroid secretion. However fetal urine production and free water clearance were reduced in fetuses of low cortisol or low aldosterone ewes. Fetal lung liquid secretion was also significantly reduced in the low aldosterone group. The glomerular filtration rate was reduced in fetuses of all adrenalectomized ewes, regardless of replacement dose. Fetal blood pressure was significantly reduced in the fetuses of low aldosterone ewes; blood flow to several fetal organs was increased in this group, indicating that decreased vascular resistance may contribute to the relative hypotension. CONCLUSION: Alterations in maternal adrenal corticosteroid levels resulted in fetal adaptation to maintain fetal blood volume despite relative maternal hypovolemia. These adaptations occurred at the expense of fetal urine and lung liquid production.     

Acute cerebral redistribution in response to invasive procedures in the human fetus.

OBJECTIVES: We sought to investigate the fetal hemodynamic response to the acute stress of invasive procedures. STUDY DESIGN: The middle cerebral artery pulsatility index was measured by Doppler ultrasonography before and after 136 invasive procedures (fetal blood sampling, transfusion, shunt insertion, tissue biopsy, and ovarian cyst aspiration). The response of fetuses submitted to invasive procedures involving transgression of the fetal body, such as intrahepatic vein blood sampling, was compared with that of control procedures at the placental cord insertion. RESULTS: The middle cerebral artery pulsatility index value fell with fetal blood sampling performed at the intrahepatic vein (median, -0.26; 95% confidence interval, -0.35 to -0.15) but not at the placental cord insertion (median, 0.05; 95% confidence interval, -0.04 to 0.19). With transfusions, the middle cerebral artery pulsatility index also fell with procedures at the intrahepatic vein (mean, -0.51; 95% confidence interval, -0.66 to -0.35) but not at the placental cord insertion (mean, -0.04; 95% confidence interval, -0.23 to 0.14). The magnitude of the response was greater with transfusions than with blood sampling alone. The middle cerebral artery pulsatility index value also fell with non-fetal blood sampling procedures involving transgression of the fetal body (mean, -0.32; 95% confidence interval, -0.56 to -0.09) but not with control non-fetal blood sampling procedures. The change in the middle cerebral artery pulsatility index was not related to gestational age, with the youngest fetus showing a fall in the middle cerebral artery pulsatility index value being at 16 weeks' gestation. Although the degree of response was weakly correlated with the duration of needling (y = -0.21 - 0.00014x; R (2) = 0.08; P =.02), multiple logistic regression demonstrated that this was instead a function of the type of the procedure. A response was seen within 70 seconds of fetal puncture. The fetal heart rate did not change significantly with procedures in any of the above-mentioned groups. CONCLUSIONS: The human fetus mounts a cerebral hemodynamic response to invasive procedures involving transgression of the fetal body, which is consistent with the brain-sparing effect.     

Normal range for fetal urine production rate customized by biometry

Objective

The aim of this study was to develop a nomogram for fetal urine production (UPR) using biometric parameters.

Methods

A cross-sectional study was performed in 110 normal singleton fetuses with gestational ages ranging from 20 to 40 weeks. UPR was measured using tridimensional ultrasound (3-DUS) virtual organ computer-aided analysis. UPR (ml/h) was calculated during the filling phase using the equation, UPR = (VFB2?VFB1)/time. The values for UPR were plotted as a function of fetal biometry (femur, humerus, abdominal circumference, and head circumference and biparietal diameter) to obtain a nomogram for each parameter.

Results

A total of 110 normal singleton fetuses with gestational age between 20 and 40 weeks were investigated. Five of them were excluded because the image quality was insufficient for correct visualization of the bladder contour. Linear regression analysis of UPR as a function of femur, humerus, abdominal circumference, and head circumference and biparietal diameter generated curves that represents the normal range for UPR by fetal biometry, and expressed by the following equations: (1) Humerus length (HL): ln (UPR) = ?5.9546 + 0.0958 × HL (mm); (R ² 0.6422); (2) abdominal circumference: ln (UPR) = ?1.0981 + 0.158 × AC (mm); (R ² 0.6328); (3) femur length: ln (UPR) = ?1.5133 + 0.0803 × FL (mm); (R ² 0.6611); (4) biparietal diameter ln (UPR) = ?7.8779 + 0.2368 × BPD?0.0012 × DBP²; (R ² 0.7066). Although BPD has the highest correlation coefficient (R ² 0.7066) there was no statistical significant difference between the parameters investigated for UPR prediction.

Conclusion

The use of biometric parameters for prediction of fetal UPR seems to be useful and can avoid the necessity of building local nomograms for different populations. The same strategy should be considered to other fields in fetal medicine.     

The relationship of heart rate patterns and tissue pH in the human fetus.

The relationship between different FHR patterns and fetal tissue pH in 68 high-risk gravidas in labor was analyzed. A tissue pH electrode was placed in the fetal scalp and tissue pH recorded on a fetal monitor every 15 seconds along with uterine contractions and continuous fetal heart rate. The tissue pH changes correlated with the FHR patterns in a manner consistent with current concepts of fetal stress. Trend monitoring of fetal tissue pH in labor may prove useful in the management of high-risk patients in labor.