SGA fetuses with normal umbilical artery Doppler waveforms and abnormal uterine arteries and fetal middle cerebral artery waveforms have an increased risk of developing distress and being delivered by emergency Cesarean section. Particularly when both uterine and fetal cerebral waveforms are altered at the same time, the risk is exceedingly high (86%) and delivery as soon as fetal maturity is achieved seems advisable. On the other hand, when both vessels have normal waveforms, the chances of fetal distress are small (4%) and expectant management is the most reasonable choice.

Our results and the review of literature suggest that absence of the ductus venosus is associated with a high incidence of fetal anomalies and adverse outcomes, including associated malformations, chromosomal aberrations, in utero heart failure and absence of the portal vein. Heart failure and absence of the portal vein seem particularly frequent when absence of the ductus venosus is associated with a connection of the umbilical vein to either the inferior vena cava or the right atrium.

In normal fetuses the CSP should always be visualized between 18 and 37 weeks, or with a BPD of 44-88 mm. Failure to observe the CSP in this interval, or possibly the presence of a large CSP, may indicate abnormal cerebral development and warrant further investigation. Conversely, absence of the CSP prior to 18 weeks, or later than 37 weeks, is a normal finding.

ABSTRACT

The objective of this study was to assess the feasibility of using the frontal suture as an acoustic window to visualize sonographically the midline cerebral structures (transfrontal view) in midtrimester fetuses. The study design was prospective and observational. In 124 healthy fetuses and in 2 fetuses with agenesis of the corpus callosum at 19 to 24 weeks' gestation, an attempt was made to obtain a transfrontal view by using transabdominal sonography. The transfrontal view was successfully and rapidly obtained in 110 (89%) of the healthy fetuses; it always provided detailed visualization of the entire corpus callosum, cavum septi pellucidii, third ventricle, brain stem, fourth ventricle, vermis cerebelli, and cisterna magna. The anatomic information was comparable with that obtained from a median sagittal scan obtained through the anterior fontanelle. In both fetuses with agenesis of the corpus callosum, the transfrontal view provided clear evidence of the anomaly. The transfrontal view is feasible in midtrimester fetuses and allows rapid demonstration of the cerebral midline structures and the corpus callosum in particular. It may be helpful in the diagnosis or exclusion of cerebral anomalies, and at least in some cases, it may obviate the need for a transvaginal examination. The transfrontal view may also be used to standardize the scanning plane for the evaluation of the fetal facial profile.

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Current ultrasound equipment allows the antenatal identification of many central nervous system anomalies from early gestation. In selected cases, special techniques (transvaginal sonography, three-dimensional ultrasound, colour Doppler) may enhance the diagnostic potential. Diagnostic accuracy, however, remains heavily dependent upon the expertise of the sonologist. Fetal ultrasound is effective in identifying neural tube defects, although alpha-fetoprotein screening seems to yield a greater sensitivity. The sensitivity in the diagnosis of central nervous system malformations other than neural tube defects remains unclear because of the ascertainment biases of the few large prospective studies that have been carried out so far. Magnetic resonance imaging may play a major role in the evaluation of cases with suboptimal ultrasound visualization, or when specific anomalies are suspected, such as intracranial haemorrhage or migrational disorders.

No abstract