Why Early??

By now, you should have some idea about the necessity for amniocentesis. Why is there confusion about when to do an amnio and why do we prefer to do them around three months?

Fetal cells in amniotic fluid have to be growing and dividing before chromosomes become visible microscopically. Early cell culture techniques were very limited, and from 1970 to about 1990, most laboratories required a lot of cells and a lot of time for growth, analysis took 4 or 5 weeks to finish. Since amnios were done around 4 months, many women were anxiety wrecks by the time results were at last reported. Our method for safe, exact ultrasound needle guidance appeared in the American Journal of Obstetrics in 1978. During the 1980's Dr Omar Alfi of The Genetics Institute in Pasadena developed a better ways to culture fetal cells. Soon afterwards, image analysis methods were applied for virtual chromosome sorting. We collaborated with Dr Alfi in developing early amniocentesis for routine use. We were there first in the US, and all of our subsequent experience has confirmed the value and safety of this technique.

We like amnios around 10 to 11 weeks after conception, because we believe that this is the safest time for fluid sampling. The muscle wall of the uterus is much firmer and much less vascular than it will be after another month - decreasing the potential complication of hemorrhage from needle passage. The ratio of fluid to fetus is excellent, and embryoes are heavier than fluid, sinking to the bottom of the amniotic space, leaving lots of room at the top for siphoning off a bit of fluid while staying as far from the fetus as possible. About 5% of patients 11-12 weeks are rescheduled, because the uterus is not in an ideal position When we do an amnio, we expect a 99% success rate a single pass of a very small needle.

Another important reason for early diagnosis has to do with the brain:

This is a high resolution ultrasonic image of the frontal part of the brain at 16 weeks GA. It shows the cortex, the place where nerve cells proliferate and interconnect. We believe that brain growth is impaired in Down's Syndrome from lack of available fetal thyroid hormone at a critical time in development. If there is ever to be a means for improving brain development in this condition, by replacing some factor that is absent during growth of the cortex, the diagnosis has to be made as early as possible, before the rapid early phase of nerve cell proliferation in the cortex.

There was a report from a Canadian study, now several years old and still not confirmed, that had a relatively high complication rate from early amnios. The participating centers had not had any previous experience with early amnios and made the mistake of assuming that the TECHNIQUE of amniocentesis is the same early or late. WRONG. The way an amnio is done and needle selection has to be individualized to the patient and the ultrasound guidance technique has to be precise. The conclusion we draw from the Canadian multi-center trial is that patients should not have early amnios in Canada. The "statistics" that count are only those at the center where the procedure is to be performed. An amnio should not be scheduled or performed by the calendar, but rather by the stage that the physician doing the procedure is most experienced and comfortable.

The 24 Hour Reporting Plan