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Answers on p 482.
A 30 year old primigravida booked into the department of obstetrics and gynaecology at 13 weeks by her last menstrual period. There was no medical history of note. Booking abdominal ultrasound scan revealed a singleton pregnancy with a crown rump length corresponding to a gestation of 10 weeks and 4 days. This discrepancy in “dates” was attributed to her conceiving within a cycle of stopping the combined oral contraceptive pill.
Biochemical screening for Down’s syndrome and open neural tube defect (NTD) was performed at 16 weeks. Her risk for an open NTD was reported as low (0.7 multiple of the median) and her risk for trisomy 21 had decreased from an age related risk of 1:796 to a biochemical determined risk of 1:5000.
At 20 weeks she attended for her routine fetal anomaly scan. The fetus was found to have mild bilateral cerebral ventriculomegaly of 11 mm and a reduced abdominal circumference equivalent to that of a 17 week fetus. The rest of the measurements were appropriate for a fetus of 20 weeks and no other fetal or placental abnormalities were found.
She was therefore referred to the regional maternal-fetal medicine tertiary centre for further assessment. The ultrasound findings were confirmed and after counselling she underwent amniocentesis and the sample (a non-“bloody tap”) sent for karyotyping and fluorescent in situ hybridisation (FISH).
The FISH analysis reported that in 50% of the cell lines there was trisomy of chromosomes 13, 18, and 21. The other 50% of cell lines were reported as showing a diploid chromosomal complement. The karyotype of the cells grown from culture of the amniotic fluid showed a chromosomal complement of 69,XXX in 50% of the cell lines and a 46,XX complement in the remaining cell lines.
On the basis of the FISH result (before obtaining the karyotype), the ultrasound findings and counselling of sequalae, the couple decided to undergo a medical termination of pregnancy. Cordocentesis was not performed because the couple declined further invasive testing. Fetocide, which allows cardiac blood sampling, was not considered because, in compliance with the Royal College of Obstetricians and Gynaecologists guidance, the unit does not perform this invasive procedure unless the gestation of the fetus at the time of termination is greater than 21 weeks and 6 days.1
At delivery macroscopic examination showed a female infant with rockerbottom feet, talipes equinovarus, syndactyly, saddle nose, wide first web toe, micrognathia, and low set ears. Postmortem examination in addition to the above revealed only cerebral ventriculomegaly. Unfortunately no cytogenetics was obtained from fetal tissue but cytogenetic analysis of chorion revealed a 69,XXX pattern.
What is the prognosis and management of mild cerebral ventriculomegaly?
What are the causes of two cell lines in a sample of amniotic fluid after amniocentesis?
What is the “best guess” diagnosis?
Answers on p 482.
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