Human fetal ductal flow velocity waveforms relative to behavioral states in normal term pregnancy

Neurodevelopment after fetal growth restriction

Fetal growth restriction (FGR) can emerge as a complication of placental dysfunction and increases the risk for neurodevelopmental delay. Marked elevations of umbilical artery (UA) Doppler resistance that set the stage for cardiovascular and biophysical deterioration with subsequent preterm birth characterize early-onset FGR. Minimal, or absent UA Doppler abnormalities and isolated cerebral Doppler changes with subtle deterioration and a high risk for unanticipated term stillbirth are characteristic for late-onset FGR. Nutritional deficiency manifested in lagging head growth is the most powerful predictor of developmental delay in all forms of FGR. Extremes of blood flow resistance and cardiovascular deterioration, prematurity and intracranial hemorrhage increase the risks for psychomotor delay and cerebral palsy. In late-onset FGR, regional cerebral vascular redistribution correlates with abnormal behavioral domains. Irrespective of the phenotype of FGR, prenatal tests that provide precise and independent stratification of risks for adverse neurodevelopment have yet to be determined.

Neurodevelopment following fetal growth restriction and its relationship with antepartum parameters of placental dysfunction

Placental dysfunction leading to fetal growth restriction (FGR) is an important risk factor for neurodevelopmental delay. Recent observations clarify that FGR evolves prenatally from a preclinical phase of abnormal nutrient and endocrine milieu to a clinical phase that differs in characteristics in preterm and term pregnancies. Relating childhood neurodevelopment to these prenatal characteristics offers potential advantages in identifying mechanisms and timing of critical insults. Based on available studies, lagging head circumference, overall degree of FGR, gestational age, and umbilical artery (UA), aortic and cerebral Doppler parameters are the independent prenatal determinants of infant and childhood neurodevelopment. While head circumference is important independent of gestational age, overall growth delay has the greatest impact in early onset FGR. Gestational age has an overriding negative effect on neurodevelopment until 32-34 weeks' gestation. Accordingly, the importance of Doppler status is demonstrated from 27 weeks onward and is greatest when there is reversed end-diastolic velocity in the UA or aorta. While these findings predominate in early-onset FGR, cerebral vascular impedance changes become important in late onset FGR. Abnormal motor and neurological delay occur in preterm FGR, while cognitive effects and abnormalities that can be related to specific brain areas increase in frequency as gestation advances, suggesting different pathophysiology and evolving vulnerability of the fetal brain. Observational and management studies do not suggest that fetal deterioration has an independent impact on neurodevelopment in early-onset FGR. In late-onset FGR further research needs to establish benefits of perinatal intervention, as the pattern of vulnerability and effects of fetal deterioration appear to differ in the third trimester.

The ductus arteriosus

The ductus arteriosus is a large vessel which connects the pulmonary trunk with the aorta. During fetal life it serves together with the foramen ovale as a shunt at cardiac level. Due to a complex regulatory mechanism it is capable of maintaining patency during fetal life and of rapid closure after birth. However, in premature neonates ductal patency frequently persists, an occurrence which may even be favourable in some situations. Recent investigations on the ductus arteriosus have provided new information about the regulatory mechanisms involved with its function. Initially, most studies on the fetal ductus arteriosus were conducted in animals. With the introduction of the combined use of two dimensional real-time and Doppler ultrasound systems the opportunity became available to study blood flow within the ductus arteriosus in the human fetus and neonate in a noninvasive manner. The increasing use in obstetric care of cyclo-oxygenase inhibitors for tocolysis and for prevention of the development of pregnancy induced hypertension and pre-eclampsia justifies the re-evaluation of the potential adverse effects of these drugs on the ductus arteriosus.

The ductus venosus

The ductus venosus is a blood vessel functioning exclusively in the fetal circulation. According to many reports it was described for the first time by Giulio Cesare Arantius (Bologna 1530–1589) in his bookDe humano foetu libellus(1563) and it is often referred to as the ductus Arantii. Thorough research, however, has made it clear that Andreas Vesalius described this vessel in 1561 in his bookExamen observationium Falloppii, which was published three years later. Moreover, it has been pointed out that the first and second editions of Arantius’s book did not contain a description of the ductus venosus but that this appeared in the 1571 edition.

Fetal behaviour in normal and compromised fetuses. An overview

Fetal intrauterine behaviour is not a stable situation but a continuous alternation of states characterized by significant changes in fetal motility, heart rate, hemodynamics, metabolism and response to stimulation. Associations between fetal heart rate patterns and movements occur from 26-28 weeks of gestation onwards. As fetuses grow older these variables become gradually more related temporally and clustered in behavioural states similar to those present in newborns. This article describes the technique of recording and analyzing fetal behaviour, its development in normal pregnancy and its influence on different physiological parameters that are assessed in clinical practice. Furthermore the deviations from the norm occurring in compromised fetuses are described.

Inferior vena cava flow velocity waveforms relative to fetal behavioural states and sample site in normal term pregnancy

Reproducibility and behavioural state dependency of flow velocity waveforms from the proximal and distal part of the fetal inferior vena cava were studied in a total of 27 normal pregnancies at 36-39 weeks of gestation. Within patient coefficients of variation in fetal inferior vena cava waveform recording were markedly higher for the proximal part compared with the distal part. This is also reflected by lower reliability values as a measure of the relative proportion of within patient and between patient variance components. No statistically significant changes in flow velocity values could be detected at proximal and distal level of the fetal inferior vena cava relative to fetal behavioural states. A marked difference in flow velocity values was, however, observed between the two measuring sites with the highest velocities at proximal level. Since a considerable variation in fetal inferior vena cava flow recording was established, a possible behavioural state related modulation may have been obscured by these waveform variabilities.

Behavioural states and cardiovascular dynamics in the human fetus; an overview

Behavioural state dependent changes occur in the circulation of the normally developing human fetus at term. During fetal behavioural state 2F (active sleep), there seems to be preferential blood flow through the ductus venosus and foramen ovale into the left heart. Increased left ventricular output of well-oxygenated blood during fetal behavioural state 2F will be necessary to meet the raised energy demands both at cerebral and trunk level as demonstrated by reduced pulsatility index values in the descending aorta, renal artery and intracranial arteries during this behavioural state. The limited studies in IUGR suggest behavioural state independency in the descending aorta and internal carotid artery which may be attributed to the fetus being incapable of adjusting its circulation to the existing behavioural state in the presence of circulatory centralization.

Ductus venosus flow velocity waveforms in relation to fetal behavioural states

OBJECTIVES

To establish the reproducibility of flow velocity waveforms in the human ductus venosus and to assess the influence of fetal behavioural states on these waveforms in normal term fetuses.

DESIGN

Reproducibility of Doppler waveform recording and analysis was studied in 10 normal pregnancies. The relation between ductus venosus flow velocities and behavioural states was investigated in 19 other term fetuses. Time-averaged, peak systolic, peak diastolic velocity, peak systolic/diastolic ratio and period time were calculated in both cross sectional studies.

SETTING

Outpatient clinic, department of obstetrics (prenatal diagnosis section), Academic Hospital, Rotterdam--Dijkzigt.

SUBJECTS

Twenty-nine women with normal singleton pregnancies at 36 to 39 weeks of gestation, resulting in uncomplicated births of healthy infants.

RESULTS

Within-patient coefficients of variation, ductus venosus waveform recordings were approximately 8 to 10% except for the peak systolic/diastolic ratio (4.3%). A decrease of approximately 30% was established for peak systolic, peak diastolic velocity and time-averaged velocity during behavioural state 1F (quiet sleep) as compared with state 2F (active sleep).

CONCLUSIONS

Flow velocity waveform recording in the ductus venosus demonstrates acceptable reproducibility. Fetal behavioural state-dependent changes were observed, suggesting a redistribution of umbilical venous blood through the ductus venosus shunt during the quiet sleep state.

There are no rest-activity dependent changes in fetal ductus arteriosus flow velocity patterns at 27-29 weeks of gestation

Blood flow velocity waveforms recorded in the fetal ductus arteriosus were related to fetal heart rate pattern (FHRP) in 13 normal pregnancies at 27-29 weeks of gestation. Recording time was always 65 min or more. In three women no low fetal heart rate (FHRP-A) variability was present, in the remaining 10 women high fetal heart rate (FHRP-B) variability was established in 80% of the recording time. There was no statistically significant difference between FHRP-A and FHRP-B pattern for all ductal flow velocity parameters, indicating rest-activity state independency in late second and early third trimester pregnancy.

Fetal cardiac flow velocities in the late 1st trimester of pregnancy: a transvaginal Doppler study

In 30 normal women with a singleton pregnancy, transvaginal Doppler ultrasound was used to record flow velocity at the fetal atrioventricular (AV) valve and outflow tract levels (ascending aorta and pulmonary artery) at 11 to 13 weeks of gestation. Technically acceptable flow velocity waveforms were recorded at the AV valve level in 19 fetuses and in the ascending aorta and pulmonary artery in 15 and 17 fetuses, respectively. Successful documentation of both transmitral and transtricuspid flow velocity waveforms was achieved in six fetuses only. Peak velocities during atrial contraction (A wave) were nearly twice as high as those during early diastolic filling (E wave), reflecting low ventricular compliance. Peak and time-averaged flow velocities in the outflow tract were lower than those observed in 2nd and 3rd trimester pregnancies with mean values of 32.1 +/- 5.4 (+/- SD) and 11.2 +/- 2.2 cm/s, respectively, in the ascending aorta and 29.6 +/- 5.1 and 10.8 +/- 2.1 cm/s in the pulmonary artery.

Human fetal foramen ovale flow velocity waveforms relative to behavioral states in normal term pregnancy

In 16 normal pregnancies the relationship between foramen ovale flow velocity waveforms and fetal behavioral states at 37 to 38 weeks' gestation was studies with Doppler techniques. Foramen ovale flow velocity waveforms are characterized by a typical systolic/diastolic component. Average flow velocity was statistically significantly increased in behavioral state 2F (active sleep) as compared with state 1F (quiet sleep), which was mainly determined by an increase in flow velocity during the end-systolic and passive atrial filling phase. The increase in the average flow velocity at the foramen ovale level during active sleep suggests a redistribution of blood flow at the cardiac level, resulting in an increased right-to-left shunt.

Ductus arteriosus flow velocity modulation by fetal breathing movements as a measure of fetal lung development

A test is needed that would accurately predict favorable neonatal lung performance in the presence of prolonged severe oligohydramnios caused by ruptured membranes so that optimal obstetric care can be provided. We propose such a test that is based on the degree of modulation of fetal ductal blood flow velocity by fetal breathing movements after maternal glucose loading. In a prospective cross-sectional study of 49 normal pregnancies (50 fetuses) between 25 and 38 weeks an exponential increase in breathing-related ductal blood flow velocity modulation was observed with advancing gestational age, reflecting the developing pulmonary vascular bed. Fetal ductal flow velocity waveforms were also recorded in 13 cases of prolonged severe oligohydramnios after ruptured membranes before 28 weeks' gestation. Normal ductal blood flow velocity modulation values were associated with normal neonatal lung performance, whereas reduced ductal blood flow velocity modulation values were associated with pulmonary hypoplasia. Fetal breathing-related ductal flow velocity modulation appears to be a promising predictor of neonatal lung performance.

Effects of behavioural states on cardiac output in the healthy human fetus at 36-38 weeks of gestation

Doppler velocity waveforms from atrioventricular valves were recorded in 20 healthy fetuses at 36--38 weeks of gestation during both behavioural states 1F (quiet sleep) and 2F (active sleep). No significant changes were found in the ratios between the velocities during early passive ventricular filling and active ventricular filling (E/A ratios) at the level of both mitral and tricuspid valves when the measurements obtained during states 1F and 2F were compared. Moreover, during state 2F the left ventricular output increased and the right ventricular output decreased, resulting in a marked modification of the right to left cardiac output ratio. Our data suggest a redistribution of cardiac output in favour of the left side of the heart during state 2F.