Qualitative and quantitative study of fetal posterior fossa during the first trimester in a Chinese population

Background

To establish the normal reference ranges for parameters related to the fetal posterior fossa in the first trimester (11 ~ 13+6 weeks of gestation) and to analyze the relationship between them and crown-rump length (CRL) among the Chinese population.

Methods

Singleton pregnancies of 11 ~ 13⁺⁶ weeks (CRL:45 ~ 84 mm) with both parents from China were randomly selected from January 2021 to November 2021. The related parameters of the posterior fossa including cisterna magna (CM), intracranial translucency (IT), brain stem (BS), brain stem to the occipital bone (BSOB), and brain stem/brain stem to occipital bone (BS/BSOB) were evaluated and measured in nuchal translucency (NT) mid-sagittal section clearly by an experienced sonographer (operator 1). To assess the reproducibility of the measurements, we randomly selected 50 pregnant women. According to the blind method, operators 1 and 2 respectively screened and measured relevant parameters. In addition, operator 1 examined and measured relevant parameters again 2 h after the first.

Results

This study included 1663 fetuses. All fetuses can clearly show the three spaces of the fetal posterior fossa. The ICCs (95% CI) of intra-operator reproducibility of CM, IT, BS, BSOB, BS/BSOB were 0.981 (0.952 ~ 0.991, P < 0.001), 0.929 (0.866 ~ 0.961, P < 0.001), 0.970 (0.946 ~ 0.983, P < 0.001), 0.991 (0.974 ~ 0.996, P < 0.001), 0.939 (0.892 ~ 0.965, P < 0.001), respectively; The ICCs (95% CI) of inter-operator reproducibility 0.926 (0.860 ~ 0.960, P < 0.001), 0.810 (-0.083 ~ 0.940, P < 0.001), 0.820 (0.645 ~ 0.904, P < 0.001), 0.804 (0.656 ~ 0.888, P < 0.001), 0.772 (0.599 ~ 0.871, P < 0.001), respectively. There was a linear correlation between CRL and the parameters related to the posterior fossa (CM, IT, BS, BSOB, BS/BSOB). CM (mm) = -1.698 + 0.532 × CRL (cm) (r = 0.829, P < 0.001); IT (mm) = 0.701 + 0.179 × CRL (cm) (r = 0.548, P < 0.001); BS (mm) = 0.403 + 0.349 × CRL (cm) (r = 0.716, P < 0.001); BSOB (mm) = -0.277 + 0.719 × CRL (cm) (r = 0.829, P < 0.001); BS/BSOB = 0.747—0.021 × CRL (cm) (r = 0.196, P < 0.001).

Conclusions

Qualitative and quantitative assessment of the fetal posterior fossa structure was feasible in the first trimester. We constructed the normal reference ranges of CM, IT, BS, BSOB, and BS/BSOB. Furthermore, CM, IT, BS, and BSOB were positively correlated with CRL, but BS/BSOB was negatively correlated with CRL.

First trimester examination of fetal anatomy: clinical practice guideline by the World Association of Perinatal Medicine (WAPM) and the Perinatal Medicine Foundation (PMF)

This recommendation document follows the mission of the World Association of Perinatal Medicine in collaboration with the Perinatal Medicine Foundation. We aim to bring together groups and individuals throughout the world for precise standardization to implement the ultrasound evaluation of the fetus in the first trimester of pregnancy and improve the early detection of anomalies and the clinical management of the pregnancy. The aim is to present a document that includes statements and recommendations on the standard evaluation of the fetal anatomy in the first trimester, based on quality evidence in the peer-reviewed literature as well as the experience of perinatal experts around the world.

Low torcular Herophili position and large brainstem-tentorium angle in fetuses with open spinal dysraphism at 11-13 weeks' gestation

OBJECTIVE

To evaluate whether in fetuses with open spina bifida (OSB) the tentorium can be seen to be displaced downwards and vertically oriented by the time of the 11-13-week scan and whether this is reflected in an alteration of the brainstem-tentorium (BST) angle.

METHODS

The study population was recruited between 2015 and 2020 from three fetal medicine referral centers and comprised a control group and a study group of pregnancies with OSB. The control group was recruited prospectively and included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome. The study group was selected retrospectively and included all cases with OSB between 2015 and 2020. All cases underwent detailed ultrasound assessment at 11 + 0 to 13 + 6 weeks' gestation. The position of the torcular Herophili (TH) was identified in the midsagittal view of the fetal brain with the use of color Doppler and was considered as a proxy for the insertion of the tentorium on the fetal skull. The BST angle was calculated in the same view and was compared between the two groups.

RESULTS

Sixty normal fetuses were included in the control group and 22 fetuses with OSB in the study group. In both groups, the BST angle was found to be independent of gestational age or crown-rump length (P = 0.8815, R²  = 0.0003861 in the controls, and P = 0.2665, R²  = 0.00978 in the OSB group). The mean BST angle was 48.7 ± 7.8° in controls and 88.1 ± 1.18°, i.e. close to 90°, in fetuses with OSB. Comparison of BST-angle measurements between the control group and cases with OSB showed a statistically significant difference (P = 0.0153). In all fetuses with OSB, the downward displacement of the TH and tentorium was clearly visible at the 11-13-week scan.

CONCLUSIONS

In fetuses with OSB, the BST angle is significantly larger than in normal controls, with the tentorium being almost perpendicular to the brainstem. This sign confirms the inferior displacement of the tentorium cerebelli with respect to its normal insertion on the occipital clivus as early as the first trimester of pregnancy and is useful in the diagnosis of Chiari-II malformation at this early stage. In fetuses with OSB, the low position of the tentorium and TH is clearly visible, even subjectively, at the 11-13-week scan. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

The importance of first trimester screening of cranial posterior fossa in predicting posterior fossa malformations which may be identified in the following weeks of gestation

PURPOSE

We aimed to investigate the value of posterior fossa ultrasonography measurements in predicting fetal posterior fossa anomaly at 11-14 weeks of gestation.

METHODS

The study was performed at Zeynep Kamil Women and Children's Diseases Training and Research Hospital. Measurements were made in two groups: the control group consisted of 328 fetuses with normal postnatal outcome and the study group consisted of 22 fetuses with enlarged 4^th ventricle. In the study group, we questioned the value of intracranial translucency (IT) and brainstem (BS) measurements and the BS/brainstem-to-occipital bone (BSOB) ratio in order to predict possible posterior fossa anomalies that may be identified in advanced gestational weeks. The differences of ultrasonographic measurements between groups with p < 0.05 were considered statistically significant.

RESULTS

IT value, BSOB value, and BS/BSOB ratio were determined as ultrasonographic variables in predicting normal development of the fetal posterior fossa, with cutoff values of 2.7, 5.1, and 0.3. Negative predictive values of these three measurements for posterior fossa abnormalities were 100%. There was no statistically significant difference between the three variables for other diagnostic accuracy values (specifities and positive predictive values) (p > 0.05).

CONCLUSION

IT, BSOB, and BS/BSOB ratio can be used as ultrasonographic markers to predict the normal development of the fetal posterior fossa.

First-Trimester Cranial Ultrasound Markers of Open Spina Bifida

OBJECTIVES

To evaluate cranial ultrasound markers during a first-trimester routine ultrasound examination for screening for open spina bifida (OSB).

METHODS

Midsagittal and axial images of the fetal head obtained from fetuses with spina bifida and unaffected control fetuses at 11 weeks to 13 weeks 6 days were analyzed retrospectively. The observed markers of the posterior brain included the 4- versus 3-line view, the brain stem (BS)-to-brain stem-occipital bone (BSOB) distance ratio (BS/BSOB), the position relationship between the maxillo-occipital (MO) line and the midbrain-BS junction, and the crash sign status.

RESULTS

This study included 9 OSB cases, 2 closed spina bifida (CSB) cases, and 200 unaffected controls. Eight of 9 OSB cases had informative midsagittal views of the head. The 3-line view (abnormal) and BS/BSOB greater than 1 (abnormal) were observed in 87.5% (7 of 8) and 100% (8 of 8), respectively. The midbrain-BS junction was below or nearly on the MO line (abnormal) in 100% (8 of 8). Seven of the cases had informative axial views of the head. The crash sign (abnormal) was observed in 85.7% (6 of 7). A 3-line view was seen in all of the cases that had a positive crash sign. Neither of the 2 cases of CSB and none of the controls had any of the 4 first-trimester intracranial ultrasound markers of OSB.

CONCLUSIONS

The 4 first-trimester intracranial ultrasound markers investigated in this study appear to be very good markers of OSB, especially a BS/BSOB greater than 1 and an abnormal MO line. The crash sign and 3-line view were observed in the same fetus. In our study, these ultrasound findings were not helpful in CSB.

First-trimester fetal neurosonography: technique and diagnostic potential

Most brain abnormalities are present in the first trimester, but only a few are detected so early in gestation. According to current recommendations for first-trimester ultrasound, the fetal head structures that should be visualized are limited to the cranial bones, the midline falx and the choroid-plexus-filled ventricles. Using this basic approach, almost all cases of acrania, alobar holoprosencephaly and cephalocele are detected. However, the majority of other fetal brain abnormalities remain undiagnosed until the midtrimester. Such anomalies would be potentially detectable if the sonographic study were to be extended to include additional anatomic details not currently included in existing guidelines. The aim of this review article is to describe how best to assess the normal fetal brain by first-trimester expert multiplanar neurosonography and to demonstrate the early sonographic findings that characterize some major fetal brain abnormalities. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Accuracy of qualitative and quantitative cranial ultrasonographic markers in first-trimester screening for open spina bifida and other posterior brain defects: a systematic review and meta-analysis

BACKGROUND

The significant number of qualitative and quantitative ultrasound markers described for first-trimester screening of open spina bifida (OSB) and other posterior brain defects (oPBD) has resulted in their complex implementation and interpretation for a widespread screening and in a lack of consensus regarding diagnostic accuracy.

OBJECTIVES

To assess and compare the accuracy of qualitative and quantitative cranial sonographic markers at 11-14 weeks of gestation for the detection of OSB and oPBD.

SEARCH STRATEGY

A systematic literature search was performed in MEDLINE and COCHRANE from 2009 to April 2020.

SELECTION CRITERIA

Studies assessing the diagnostic accuracy of quantitative and/or qualitative ultrasound signs to predict OSB and oPBD were included. Cohort studies and case-control studies were also considered.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed the risk of bias. The overall pooled estimate and a summary receiver operating characteristic curve was estimated for each subgroup (qualitative and quantitative assessment).

MAIN RESULTS

Twenty-three studies were included in our meta-analysis. The pooled sensitivity and specificity for qualitative assessment were 76.5% and 99.6%, and for quantitative assessment were 84.5% and 96.3%, respectively; specificity for the qualitative ultrasound signs was significantly higher (P = 0.001). The overall sensitivity of cranial sonographic markers for the screening of oPBD was 76.7% and specificity was 97.5%.

CONCLUSIONS

The qualitative approach demonstrated greater specificity, so this would appear to be more appropriate for daily screening, as a first-line tool, whereas the quantitative approach should be reserved for expert ultrasound.

TWEETABLE ABSTRACT

This study highlights the relevance of first-trimester qualitative ultrasound signs in the screening of open spina bifida.

First trimester cerebral appearance in the presence of closed spina bifida with myelomeningocele, part of the oeis complex

Our communication presents a prenatally detected case with severe spinal defect detected in the first trimester of pregnancy, accompanied by a large skin-covered myelomeningocele but normal cranio-cerebral structural appearance.These findings suggest that in the first trimester, the extent of the spinal defect, the cerebrospinal fluid leakage to a large, but skin-covered, meningocele and fixation of the spinal cord at the lesion are not sufficient to determine downward hindbrain displacement and the development of secondary signs for open spina bifida.Therefore, we suggest a careful evaluation of the fetal cerebral features if a meningocele is detected. The presence of the skin covering the lesion may not be evident in the first trimester, but the absence of intracranial open spina bifida markers may indicate a 'closed' spinal defect, which generally associates a good neurological outcome. Also, studies aimed to investigate the accuracy of the intracranial features for open spina bifida detection should consider the possibility of 'closed' myelomeningoceles to avoid incorrect correlations.

Ratio of fetal choroid plexus to head size: simple sonographic marker of open spina bifida at 11-13 weeks' gestation

OBJECTIVES

To measure the ratio of choroid plexus (CP) size to head size in normal fetuses and to compare it to that in fetuses with open spina bifida (OSB) and quantify the subjective sign of a 'dry brain'.

METHODS

This was a retrospective study of ultrasound images, obtained during first-trimester screening between 11 and 13 weeks of gestation, from 34 fetuses with OSB and 160 normal fetuses. From the hospital databases, we retrieved images of the fetal head in the transventricular axial plane. We measured the areas of both CPs and the head and calculated the ratio between them. We also measured the longest diameter of each CP and calculated their mean (CP length), and measured the occipitofrontal diameter (OFD) and calculated the ratio of CP length to OFD. Measurements from the OSB fetuses were plotted on crown-rump length (CRL) reference ranges constructed using data from the normal fetuses, and Z-scores were calculated.

RESULTS

In the normal fetuses, the CP area increased, while the ratios of CP area to head area and CP length to OFD decreased, with increasing CRL. In 30 of the 34 (88%) fetuses with OSB, both ratios were increased significantly and the CPs filled the entirety of the head, giving the impression of a dry brain. In these cases, the borders of the lateral ventricles could not be identified.

CONCLUSIONS

At 11-13 weeks, the majority of fetuses with OSB have reduced fluid in the lateral ventricles such that the CPs fill the head. The dry brain sign is easily visualized during routine first-trimester ultrasound examination while measuring the biparietal diameter, and can be quantified by comparing the size of the CPs to the head size. Until prospective data confirm the usefulness of this sign in screening for OSB, it should be considered as a hint to prompt the examiner to assess thoroughly the posterior fossa and spine. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Cranial sonographic markers of fetal open spina bifida at 11 to 13 weeks of gestation

OBJECTIVES

To compare the sonographic signs of spina bifida obtained on axial and sagittal views of the fetal head between 11 and 13+6 weeks of gestation.

METHODS

This was a retrospective study including 27 cases of spina bifida and 1003 randomly selected controls. Indirect markers of spina bifida were evaluated on stored ultrasound images. Intracranial translucency (IT), ratio between the brainstem and the brainstem-occipital bone distance (BS/BSOB), and maxillo-occipital (MO) line were assessed on sagittal view, whereas biparietal diameter (BPD), BPD to abdominal circumference ratio (BPD/AC), and aqueduct to occipital bone (aqueduct of Sylvius [AoS]) distance were measured on the axial plane. Reference ranges were developed, and cases of spina bifida were examined in relation to the reference range.

RESULTS

On the sagittal view, detection rates for IT below the fifth percentile, BS/BSOB above the 95th percentile, and an abnormal MO line were 52.3%, 96.3%, and 96.3%, respectively. On the axial view, detection rates for BPD, BPD/AC, and AoS below the fifth percentile were 66.7%, 70.4%, and 77.8%, respectively.

CONCLUSION

The MO line and the BS/BSOB ratio appear to be the best indirect ultrasound markers of spina bifida and can be easily obtained during the routine first-trimester scan.

Is Cisterna Magna Width a Useful First-Trimester Marker of Aneuploidy?

OBJECTIVE

To assess whether the cisterna magna (CM) width measured in first-trimester fetuses is a useful marker for aneuploidy detection.

METHODS

This was a prospective study in 2 different cohorts in a tertiary referral center. The first cohort comprised 913 fetuses from the general pregnancy population during the period 2012-2016 and was used to construct the CM reference ranges applying the λ-μ-σ (LMS) method. The second cohort included 714 high-risk fetuses undergoing chorionic villus sampling during the period 2012-2016. Mean detection rates using the 95th percentile for CM width observed in chromosomal anomaly groups were compared with those obtained in chromosomally normal fetuses.

RESULTS

The 50th percentile for CM ranged from 1.66 to 2.75 mm when crown-rump length (CRL) increased from 45 to 84 mm. Among high-risk fetuses, the following chromosomal anomalies were diagnosed in 125 (17%) fetuses: trisomy 21 (n = 63), trisomy 18 or 13 (n = 21), monosomy X (n = 9), submicroscopic anomalies (n = 11), and other anomalies (n = 22). The mean CM width for euploid fetuses was 2.4 mm (1.13 multiples of the median, MoM). While CM width was significantly increased in trisomy 21 (mean 2.7 mm; 1.23 MoM; p > 0.05), no differences were found in the other anomaly groups. Among the 63 fetuses with trisomy 21, a CM width above the 99th percentile was observed in 23 fetuses (37%).

CONCLUSIONS

The new reference range for CM width at 11-13 weeks of gestation did not differ from previous studies. In first-trimester fetuses with trisomy 21, CM width appears to be increased, although its value as an ultrasound marker is limited, because of its detection rate of 37%.

Diagnostic assessment of foetal brain malformations with intra-uterine MRI versus perinatal post-mortem MRI

PURPOSE

To evaluate differences in diagnostic yield of intra-uterine foetal (iuMR) and post-mortem MRI (PMMR) for complex brain malformations, using autopsy as the reference standard.

METHODS

In this retrospective, multicentre study spanning 2 years, we reviewed 13 terminated singleton pregnancies with a prenatal ultrasound finding of complex foetal cerebral abnormalities, referred for both iuMR and PMMR. The iuMR and PMMR studies of the brain were reported independently by two groups of radiologists, blinded to each other's reports. Descriptive statistics were used to compare differences in intracranial abnormalities with autopsy (and genetic testing, where present) as reference standard.

RESULTS

The median gestational age at termination was 24.6 weeks (IQR 22-29) with median time between delivery and PMMR of 133 h (IQR 101-165). There was full concordance between iuMR and PMMR findings and autopsy in 2/13 (15.3%) cases. Partial concordance between both imaging modalities was present in 6/13 (46.2%) and total discordance in the remainder (5/13, 38.5%). When compared to autopsy, PMMR missed important key findings specifically for neuronal migration and cerebellar anomalies, whereas iuMR appeared to overcall CSF space abnormalities which were less crucial to reaching the final overall diagnosis.

CONCLUSIONS

iuMR should be performed to improve foetal phenotyping where there is a prenatal ultrasound for complex foetal brain abnormalities. Reliance on PMMR alone is likely to result in misdiagnosis in a majority of cases.

Prospective detection and differential diagnosis of cystic posterior fossa anomalies by assessing posterior brain at 11-14 weeks

BACKGROUND

The role of the first-trimester scan has expanded from aneuploidy screening to the diagnosis of fetal malformations. Abnormal appearance of the posterior brain at 11-14 weeks gestation is a marker of cerebral anomalies; in fact an increased amount of fluid, particularly when the choroid plexus of the fourth ventricle is not visible and only 2 brain spaces instead of 3 are seen, may indicate the presence of cystic or cyst-like posterior fossa anomalies, such as Blake's pouch cyst or Dandy-Walker malformation.

OBJECTIVE

The purpose of this study was to assess the role of ultrasound scanning in the identification of cystic posterior fossa anomalies at 11-14 weeks gestation.

STUDY DESIGN

A prospective cohort study of fetuses with cystic appearance of the posterior fossa at 11-14 weeks gestation was performed. In all cases and in a control group of 40 normal fetuses, the brainstem-tentorium angle was also measured. The presence or absence of cystic posterior anomalies was determined at birth or at postmortem evaluation.

RESULTS

In the period 2014-2018, 32 fetuses with an increased brainstem-occipital bone distance and/or failure to visualize the choroid plexus of fourth ventricle (2 brain spaces) were seen. Of these, 18 fetuses were terminated in the first trimester because of associated anomalies and were excluded from the study because of unavailable autoptic findings. The remaining 14 fetuses eventually were found to have a Dandy-Walker malformation in 4 cases, a Blake's pouch cyst in 8 cases, and normal brain anatomy in 2 cases. Two brain spaces were seen in all cases with Dandy-Walker malformation and in 2 of 8 cases with Blake's pouch cyst. Both brainstem-occipital bone measurement and brainstem-tentorium angle were significantly different in fetuses with Dandy-Walker malformation, Blake's pouch cyst, and control subjects (P<.0001). The brainstem-occipital bone z-scores of fetuses with Dandy-Walker malformation and Blake's pouch cyst were always +3 or more and +1.7 or more, respectively. The brainstem-tentorium angle z-scores were always -5 or less and -0.1 or less, respectively.

CONCLUSION

Our study confirms that sonography of the posterior brain at 11-14 weeks gestation allows the identification of cystic posterior fossa anomalies. A large brainstem-occipital bone predicts Dandy-Walker malformation or Blake's pouch cyst. The presence of 2 brain spaces and a small brainstem-tentorium angle are correlated significantly with the presence of Dandy-Walker malformation.

First-trimester cystic posterior fossa: reference ranges, associated findings, and pregnancy outcomes

OBJECTIVE

To report reference ranges for fetal cerebral posterior fossa measurements and to describe the sonographic findings, karyotype results, and pregnancy outcomes in fetuses presenting with cystic posterior fossa (CPF) in the first trimester of pregnancy.

METHODS

Two groups of patients undergoing first-trimester sonographic screening at 11-13 weeks' gestation were studied. The first (control group) consisted of 253 consecutive fetuses with normal posterior fossa, in which the brainstem (BS), fourth ventricle, cisterna magna, and BS-occipital bone (BS-OB) diameter were prospectively measured and the BS/BS-OB diameter ratio was calculated. The second (study group) consisted of 14 fetuses in which a CPF was detected. Information on sonographic findings, prenatal karyotype results, and pregnancy outcomes was obtained by reviewing ultrasound reports and medical records. The results from the two groups were then compared.

RESULTS

In the control group, the size of all posterior fossa structures increased and the BS/BS-OB diameter ratio slightly decreased as the pregnancy progressed. In the study group, the BS diameter did not differ significantly from the measurements obtained in the control group. However, the BS-OB diameter and the fourth ventricle were significantly larger (p < .05 and p < .001, respectively) in the study group than in the control group. Additionally, the cisterna magna was not identified in 13 of the 14 fetuses (93%) in the study group, in comparison to zero out of the 253 fetuses in the control group (p < .001). Finally, the BS/BS-OB diameter ratio was significantly smaller in the study group when compared with the control group (p < .05). Regarding pregnancy outcomes, 12 of the 14 (86%) affected pregnancies underwent elective termination (n = 11) or ended in an early intrauterine demise (n = 1) due to the associated chromosomal abnormalities or structural defects. The two fetuses with isolated CPF had a normal second-trimester scan and resulted in the delivery of healthy newborn infants.

CONCLUSIONS

The detection of a CPF in the first trimester is associated with a high rate of chromosomal and structural defects. By using normative data, early sonographic screening and detection of mildly and moderately abnormal cases is possible. Fetuses with isolated CPF require further study with a detailed second-trimester scan. This is essential in order to differentiate cases with poor and good perinatal outcomes. Finally, our data also demonstrate that the main sonographic tool when screening for CPF in the first trimester is the assessment of the fourth ventricle, which is significantly larger in abnormal cases as the result of the wide communication between the fourth ventricle and the cisterna magna.

Non-visualization of choroid plexus of fourth ventricle as first-trimester predictor of posterior fossa anomalies and chromosomal defects

OBJECTIVE

To assess non-visualization of the choroid plexus of the fourth ventricle (CP-4V) as a simple, qualitative and reproducible first-trimester ultrasound feature of the posterior fossa for the prediction of central nervous system (CNS) anomalies and chromosomal defects.

METHODS

First-trimester three-dimensional ultrasound datasets of the fetal brain were obtained prospectively from 65 consecutive normal singletons and retrospectively from 27 fetuses identified as having an abnormal posterior fossa on first-trimester ultrasound examination, and randomly combined to form the final study group. The stored ultrasound volumes were analyzed offline by two accredited sonologists, who were not aware of the final diagnoses. The CP-4V was assessed by multiplanar navigation and classified as visible or non-visible in its normal position depending on whether or not the echogenic structure that separates the fourth ventricle from the cisterna magna was identified in both midsagittal and axial planes. Correlation with subsequent second-trimester ultrasound, fetal magnetic resonance imaging, or postmortem or postnatal findings was performed to determine the predictive value of the first-trimester findings.

RESULTS

Among the 92 ultrasound datasets analyzed, 73 (79%) were acquired transabdominally and 19 (21%) transvaginally. The CP-4V was classified as visible in 64 cases and non-visible in 28 cases, with agreement between the two observers in both sagittal and axial planes in all but one case. Twelve of the 28 (43%) fetuses with non-visible CP-4V were subsequently diagnosed as having a CNS malformation (open spina bifida (n = 6), Dandy-Walker malformation (n = 2), Blake's pouch cyst (n = 2), cephalocele (n = 1) and megacisterna magna (n = 1)). In addition, 20 of these 28 (71%) fetuses had aneuploidy (trisomy 18 (n = 10), triploidy (n = 5), trisomy 13 (n = 3), Turner syndrome (n = 1) or trisomy 21 (n = 1)). There was only one false-positive case, in which the CP-4V was classified as absent in a normal fetus.

CONCLUSIONS

Non-visualization of the CP-4V in the first trimester appears to be a strong marker of posterior fossa anomalies and chromosomal defects. Qualitative evaluation of this anatomic structure is simple, feasible and reproducible, and its routine assessment during the first-trimester scan may facilitate the early detection of CNS anomalies and associated fetal aneuploidy. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Prevalence of Neural Tube Defects and the Impact of Prenatal Diagnosis in Three Districts of Beijing, China

BACKGROUND

The objectives of this study were to explore the prevalence of neural tube defects (NTDs) in three districts of Beijing, and to evaluate the impact of prenatal diagnosis on the prevalence.

METHODS

Data were collected between 2006 and 2012 from the Beijing Birth Defects Surveillance System. P₁₃ and P₂₈ represent the prevalence of NTDs diagnosed from 13 weeks and 28 weeks of gestation, respectively, to 7 days after delivery. Populations were classified as household (permanent) and non-household (non-permanent) because differences exist in access to health care, education, and income, among others.

RESULTS

The P₁₃ of NTDs was 11.7 per 10 000 births in the three districts, which declined from 2006-12. In addition, the prevalence of NTDs in the non-household population was 1.7-fold higher than that among the household population. The P₁₃ of anencephaly, spina bifida, and encephalocele were 5.3, 4.9, 1.6, respectively, per 10 000 births. The P₂₈ of NTDs only represented 29.1% of P₁₃ , and this proportion decreased over the 7-year period.

CONCLUSIONS

The prevalence of NTDs remains high in the three districts of Beijing, and the rate was higher in the non-household than household population. The prevalence of birth defects would be under estimated by almost 70 per cent if the report time was set on 28 weeks' gestation or later compared with report time on 13 weeks of gestation. It is better to set the report time earlier in birth defect surveillance in contemporary China.

Sonographic detection of central nervous system defects in the first trimester of pregnancy

The fetal central nervous system can already be examined in the first trimester of pregnancy. Acrania, alobar holoprosencephaly, cephaloceles, and spina bifida can confidently be diagnosed at that stage and should actively be looked for in every fetus undergoing first-trimester ultrasound. For some other conditions, such as vermian anomalies and agenesis of the corpus callosum, markers have been identified, but the diagnosis can only be confirmed in the second trimester of gestation. For these conditions, data on sensitivity and more importantly specificity and false positives are lacking, and one should therefore be aware not to falsely reassure or scare expecting parents based on first-trimester findings. This review summarizes the current knowledge of first-trimester neurosonography in the normal and abnormal fetus and gives an overview of which diseases can be diagnosed.