John D. Stephens

Prenatal Genetic Diagnosis in 3000 Amniocenteses

We analyzed 3000 consecutive amniocenteses for prenatal diagnosis to assess the frequency of abnormalities, safety of the procedure, technical and interpretive difficulties and overall diagnostic accuracy. Chromosomal abnormalities were detected in 2.4 per cent of the 2404 pregnancies tested because of advanced maternal age (greater than or equal to 35 years), in 1.2 per cent of 240 monitored because of prior trisomy 21 and in 9.1 per cent of 55 examined for other cytogenetic indications. Mosaicism was detected in 0.4 per cent, and unexpected translocations in 0.4 per cent. Amniotic fluid was obtained on the first attempt in 99.3 per cent of the last 1000 cases, and cultures established from 99.7 per cent of patients attending our clinic. The fluid was discolored in 1.2 per cent of patients, a quarter of whom had missed abortions. The rate of spontaneous abortion after amniocentesis was 1.5 per cent. There were 14 diagnostic errors, six serious enough to affect the outcome of pregnancy. The karyotyping error rate was 0.07 per cent. We conclude that prenatal diagnosis is safe, highly reliable and extremely accurate.

Management of the fetus with an abdominal wall defect

Eleven fetuses with omphalocele and two with gastroschisis were diagnosed by prenatal ultrasonographic examination. Intact omphalocele was accurately distinguished from gastroschisis by detection of a membranous sac covering the herniated viscera, by liver protruding from the abdomen, and by the frequent association of major structural anomalies. Gastroschisis was characterized by the absence of these findings and the presence of bowel loops floating freely in the amniotic fluid. Nine of eleven fetuses with omphaloceles had other major malformations and did not survive. Two small omphaloceles and two gastroschises were correctly diagnosed as isolated defects, free from associated anomalies. All four underwent maternal transport and were successfully managed with good outcome. Prenatal ultrasonography allows rational decisions about perinatal management by distinguishing between omphalocele and gastroschisis and by screening for associated anatomic defects. Karyotype analysis should be a part of the prenatal workup. Most isolated defects can be followed and delivered normally near term. Accurate prenatal diagnosis allows maternal transport and in a few cases may alter the timing or mode of delivery.

Prenatal diagnosis of osteogenesis imperfecta type II by real-time ultrasound

SummaryBy comparing fetal femur length to biparietal diameter a fetus at risk for osteogenesis imperfecta type II was diagnosed in the early second trimester of pregnancy. Real-time ultrasound is a reliable non-invasive technique for the prenatal diagnosis of fetal dwarfism syndromes.