Ultrasound of the placenta: a systematic approach. Part I: Imaging

Fetal cerebral periventricular halo at midgestation: an ultrasound finding suggestive of fetal cytomegalovirus infection

OBJECTIVE

The objective of the study was to identify a cerebral ultrasound finding indicative of fetal cytomegalovirus (CMV) infection at midgestation.

STUDY DESIGN

All fetuses of 218 patients with primary CMV infection underwent prospective transvaginal neurosonographic examination at 20-22 weeks' gestation.

RESULTS

Transvaginal sonography identified a periventricular echogenic halo with well-defined borders in 6 infected fetuses at a mean gestational age of 20.5 weeks. Transabdominal axial views of the fetal head were normal in all cases. All patients opted for termination of pregnancy. Autopsy in 2 fetuses showed changes compatible with subacute white matter injury resembling telencephalic leukomalacia.

CONCLUSION

A fetal cerebral periventricular halo disclosed by transvaginal sonography at midgestation in pregnant patients with recent CMV infection is suggestive of fetal infection and may be associated with white matter lesions.

Imaging during pregnancy

The use of imaging techniques in women who are pregnant has increased greatly over the past decade. This focused review discusses the risks and indications of ultrasonography, magnetic resonance imaging, computed tomographic scanning, and fluoroscopy for the evaluation of the parturient with non-obstetric disorders. Diagnostic imaging of the pregnant woman for the evaluation of disorders not related to pregnancy is evolving, and protocols will vary from institution to institution. The potential benefit from indicated diagnostic radiological procedures in the parturient nearly always outweighs risk to the fetus because radiation exposure from a single procedure conveys little fetal risk.

Placental blood flow and the risk of preterm delivery

The goal of this analysis was to estimate the influence of variation in uterine artery and umbilical artery resistance indices (RIs) measured across gestation on variation in the risk of preterm delivery (PTD). Analyses were carried out on data collected in a longitudinal study of 523 gravidas. Uterine and umbilical artery RIs were measured on three occasions during pregnancy (16-20 weeks gestation; 21-29 weeks gestation; and 30-36 weeks gestation). Data were analyzed using the Cox proportional hazards regression model. The primary outcome variable was birth prior to 37 weeks gestation. We found that for mothers who delivered preterm the mean uterine artery RI was consistently larger across all gestational ages, while the mean umbilical artery RI decreased significantly more slowly across gestation than for their term counterparts. In analyses pooled by type of delivery, we found that the hazard ratio (HR) for PTD was statistically significant for either uterine artery RI (HR=2.26, 95% CI: 1.65, 3.11) or umbilical artery RI (HR=3.47, 95% CI: 2.43, 4.95) after adjusting for statistically significant covariates. In stratified analyses, the hazard ratio for PTD was also positively associated with an increased uterine or umbilical artery RI in both spontaneous and indicated deliveries. Our data suggest that pregnancies with either a higher uterine or umbilical artery RI across gestation are more likely to be affected by PTD suggesting that disordered placentation resulting in compromised placental blood flow may be an important pathway to PTD.

Recognising gestational trophoblastic disease

Gestational trophoblastic disease (GTD) is a group of interrelated tumours originating from the placenta. Hydatidiform molar (HM) pregnancy is the most common form of GTD; this includes both partial hydatidiform molar (PHM) and complete hydatidiform molar (CHM) pregnancies. The importance of such a condition derives from its potential for persistent trophoblastic disease; this is noted to be more common after a CHM (10-20%) compared to a PHM (0.1-11%). The recent routine use of high-resolution trans-vaginal ultrasound (TVS) in early pregnancy has improved the recognition and thus pre-surgical diagnosis of molar pregnancy. Pre-surgical recognition aids planning of surgery, decreases intra-operative complications and identifies women with potential persistent trophoblastic disease. Despite the introduction of TVS, its performance in preoperative diagnosis is quite poor. This is primarily because of the histomorphometric features of the hydropic villi. A significant proportion of HM cases demonstrates minimal hydropic change in the first trimester and therefore is likely to remain unidentifiable by ultrasound examination prior to surgical evacuation, even with improved sonographer expertise. The overall sensitivity for the ultrasound diagnosis of HM is 50-86%. Ultrasound diagnosis of CHM can be made in approximately 80% of the cases, whilst ultrasound diagnosis of PHM is less accurate and nearly 70% of cases will be missed. Correlation of the ultrasonographic findings with human chorionic gonadotropin levels can further improve the recognition of HM pregnancy pre-surgery. Although ultrasound can be helpful in the diagnosis of molar pregnancies, histological confirmation is mandatory. Histological confirmation post-curettage is still the gold standard for the diagnosis of GTD. In this article, we critically evaluate the role of TVS in the pre-surgical recognition of GTD.

Ultrasound of the placenta: a systematic approach. Part II: functional assessment (Doppler)

Doppler velocimetry is the ideal clinical tool to assess placental performance in high-risk pregnancies. It also has value in predicting later complications and outcome in pregnancies which appear uncomplicated. All three circulations (fetal, placental and maternal) may be interrogated by Doppler technology. In the following review, we present basic physics aspects of Doppler and discuss mainly Doppler investigation of the fetal-placental circulation (umbilical artery, intraplacental circulation) as well as the uterine arteries. The assessment of umbilical blood flow provides information on blood perfusion of the fetal-placental unit. The diastolic blood flow velocity component in umbilical artery increases with advancing gestation. In pregnancies complicated by placental dysfunction, there may be a reduction in the number of functional villi and/or small blood vessels with, as a result, increased impedance, reflected, mainly, by a decrease in end-diastolic velocity. When the resistance increases even more, there is no diastolic forward velocity (absent end-diastolic velocity). Further increase in the resistance causes reversed end-diastolic velocity, which is considered a late step in the cascade of events leading to intrauterine fetal demise. Doppler assessment of the umbilical arteries was found to improve outcome of high-risk pregnancies, and reduce hospital admissions. On the contrary, routine Doppler ultrasound in low risk or unselected populations does not seem to confer benefit on mother or newborn. Uterine artery Doppler is a useful test in predicting pregnancies at high risk of developing complications related to uteroplacental insufficiency. It identifies women who may benefit from increased antenatal surveillance or prophylactic therapy. Three-dimensional power Doppler sonography can provide new insights into placental pathophysiology.