Sensitivity of fetal anomaly detection as a function of time

Incidence of fetal anomalies after incomplete anatomic surveys between 16 and 22 weeks

OBJECTIVE

Midtrimester fetal anatomic surveys by ultrasound are a standard obstetrical practice. As technology has improved, anatomic surveys are increasingly performed at earlier gestational ages. Ultrasound's ability to detect anomalies may be limited before 20 weeks, thereby increasing the likelihood of an incomplete survey. We sought to determine factors contributing to incomplete sonograms and the likelihood of fetal anomalies identified on subsequent examinations.

STUDY DESIGN

We conducted a retrospective case-control study by comparing incomplete anatomic surveys from 2004 to 2009 at the University of Washington to an identical number of examinations where the study was completed successfully. Patients with multiple gestations, anomalies, and surveys performed outside of the range of 16 to 22 weeks were excluded.

RESULTS

One thousand thirty incomplete and complete surveys were identified. Maternal body mass index and early gestational age less than 18 weeks were associated with incomplete examinations. Incomplete visualization of the cardiac structures and spine were the most common reasons for an incomplete survey. Almost 40% of these incomplete examinations were completed on subsequent ultrasound (mean number of ultrasounds: 2). Five percent had a fetal anomaly or aneuploidy marker identified on subsequent ultrasound.

CONCLUSION

Incomplete anatomic surveys were associated with gestational age less than 18 weeks and maternal habitus. Five percent of patients had anomalies or aneuploidy markers on subsequent scans, and the majority of these were cardiac defects were cardiac defects. No spine abnormality was detected in any fetus with incomplete visualization of the spine with normal intracranial anatomy. These data that indicate the optimal timing for anatomic survey is beyond 18 weeks and more than 20 weeks for patients with body mass index greater than 30 kg/m and highlight the importance of subsequent ultrasounds to complete anatomy surveys.

Short-term outcome of isolated and associated congenital heart defects in relation to antenatal ultrasound screening

OBJECTIVE

To investigate the outcome of fetuses affected by congenital heart defects (CHD), either detected or undetected at ultrasound screening, according to their complexity and severity.

DESIGN

The study group comprised 3633 malformed fetuses entered into the Eurofetus database of which 798 had CHD. We compared the short-term outcome in cases where a CHD was detected by ultrasound screening with that in cases where a CHD was not detected. Isolated and associated CHD (ICHD and ACHD) and the degree of severity of defects were considered separately. Outcome data included termination of pregnancy (TOP), intrauterine fetal death, neonatal death (< 6 days after birth), gestational age at diagnosis and at delivery, mode of delivery and birth weight.

RESULTS

Of the 798 fetuses with CHD, 595 had ICHD and 203 had ACHD. The diagnosis of an anomaly was made significantly earlier in ACHD cases. TOP was chosen in 28% of cases with a prenatal diagnosis of CHD, 20% for ICHD and 37% for ACHD (P < 0.001). The survival rate of antenatally diagnosed fetuses was lower in those with ACHD than in those with ICHD (P < 0.001) and lower for fetuses with antenatal diagnosis than with postnatal diagnosis (P < 0.001); this was due to significant differences in the complexity and severity of the defect. Premature delivery (< 32 weeks) was more frequent in fetuses in which an antenatal diagnosis of CHD had been made. Severe CHD were diagnosed earlier and were associated with a higher rate of TOP and spontaneous loss.

CONCLUSIONS

The severity of CHD has a positive influence on the sensitivity of screening but a negative influence on the outcome. CHD that are not diagnosed antenatally include a high proportion of benign malformations. This explains the apparent paradox of a poorer outcome in fetuses in which a CHD was detected prenatally compared to those fetuses in which the defect was undetected prenatally. However, prenatal diagnosis provides parents with the option of TOP or of preventive care in specialized centers.