OC56: Miscarriage after a normal scan at 12-14 gestational weeks in women at low risk of carrying a fetus with chromosomal anomaly according to nuchal translucency screening

Methods: Women presenting for their 11–14-week ultrasound scan were prospectively recruited. At the time of the scan, a transverse section of the head was obtained in all cases in order to assess ossification and shape the calvarium and choroid plexus apposition (‘butterfly’ sign). In addition, symmetry of the midline, the posterior fossa and the fetal spine were evaluated when possible. All suspected CNS malformations seen on the first-trimester ultrasound scan were re-evaluated in the early second trimester, and/or confirmed by postpartum findings. Results: During a 5-year study period, 11 cases of CNS abnormalities were detected in the first trimester, including holoprosencephaly (n = 5), acrania (n = 3), and one case each of cephalocele, spina bifida and iniencephaly. In addition, three cases of severe xyphoscoliosis were also detected, all of which were associated with a body stalk anomaly. All cases of holoprosencephaly were associated with chromosomal abnormalities. Three of the other six cases had chromosomal analyses performed prenatally; all revealed a normal karyotype. The first-trimester diagnosis of the fetal CNS anomaly was confirmed on second-trimester ultrasound or postpartum in all cases. Review of the cases in which no CNS abnormalities were detected on the 11–14-week scan revealed two additional cases of spina bifida and one case of severe hydrocephaly, both diagnosed in the mid-trimester. Conclusions: Ultrasound screening at 11–14 weeks is a powerful tool for the early diagnosis of severe congenital anomalies of the fetal brain, including holoprosencephaly and acrania. However, its role in detecting cases of spina bifida is still limited, although most severe cases of spinal dysraphism may be easily recognizable during this gestational age by a systematic examination of the fetal spine.