A false-positive diagnosis of Turner syndrome by amniocentesis

Fetal sex discordance

Fetal sex discordance is an entity that is becoming more frequent due to the expansion of the cfDNA for prenatal diagnosis. Its incidence can be estimated in 1/1500-2000 pregnancies, a frequency as high as that of some common chromosomopathies. The causes of this phenomenon are multiple and diverse, ranging from laboratory errors to important pathologies such as disorders of sexual differentiation. The management of a case of fetal sex discordance must be structured, starting with the review of the clinical history and the tests performed, and may require the performance of invasive tests to reach a diagnosis. Prevention through adequate pretest counseling and ultrasound confirmation can help to reduce its incidence.

The introduction of QF-PCR in prenatal diagnosis of fetal aneuploidies: time for reconsideration

Quantitative fluorescent polymerase chain reaction (QF-PCR) has recently entered the field of prenatal diagnosis to overcome the need to culture fetal cells, hence to allow rapid diagnosis of some selected chromosomal anomalies. We reviewed the studies on the accuracy of QF-PCR in detecting chromosomal anomalies at prenatal diagnosis. Overall, 22 504 samples have been analysed. The detection rate of aneuploidies of the selected chromosomes (13, 18 and 21, and X and Y) was 98.6% (95% confidence interval 97.8-99.3). QF-PCR might play a major role and be considered a valid alternative to the full karyotype. Being less expensive, and almost entirely automated, more women could undergo invasive prenatal diagnosis without significant increase in health expenditure. By using QF-PCR as a stand-alone test, the chances of non diagnosing the commonest, and the only chromosome anomalies which do increase in frequency with maternal age, are approximately one in 150 abnormal karyotypes, or one in 10-30 000 samples, based on the age distribution. These error rates might be deemed acceptable, although most structural chromosomal anomalies will be missed. At present, women are rarely informed about the full spectrum of the conditions which might be diagnosed via amniocentesis or chorionic villous sampling. Some of these anomalies might be acceptable, in view of their limited or uncertain clinical relevance, and decision analysis might, in the majority of cases, confine the full karyotype to selected women who have specific indications.

Prenatal karyotype and ultrasound discordance in intersex conditions

An infant born at 38 weeks' gestation with ambiguous genitalia had a prenatal 45X karyotype but an enlarged phallus on an ultrasound scan at 31 weeks' gestation. The newborn examination demonstrated penoscrotal hypospadias with chordee and two gonads palpable in the scrotum with a right hydrocele. Ultrasound showed a saccular structure containing debris behind the bladder. The postnatal karyotype was revealed to be 45X/46XY, with a pseudodicentric Y chromosome. Cystoscopy/genitography identified a uterus and a right fallopian tube, which were removed along with a dysgenetic right gonad. Biopsy of the descended left gonad revealed rare germ cells. The final diagnosis was 45X/46XY male pseudohermaphroditism with testicular dysgenesis. One should be aware of possible chromosomal mosaicism and combine the prenatal karyotype with the ultrasound genital findings to formulate an intersex differential diagnosis.