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By John C. Hobbins, MD
In 1955, the following statement appeared in the Lancet: "Although transabdominal puncture of the uterus has been carried out often for therapeutic and experimental reasons without accident, mere curiosity does not justify the procedure and its practical value in probably limited in the human. If the results are confirmed in animals, however, it might become of great significance in veterinary practice."
Despite this prophecy, in the 1970s, amniocentesis was offered to many patients of the AMA, simply because it became possible to do karyotypic analysis on cultured amniocytes. Amniocentesis at that time involved introducing a needle into the uterus midway between the patient’s uterine fundus and the symphysis pubis. Sometimes ultrasound was used to mark a preferable needle insertion site, after which the patient walked to another area where a clinician would insert a needle through the "marked" area. Later real-time ultrasound enabled the operator to guide a needle into a desired place under simultaneous ultrasound guidance. Although data were sparse, the observation that the risk of the pre real-time amniocentesis seemed to be only marginally greater than the post real-time method was a testimonial to the resilience of pregnancy in general. Nevertheless, this technique does carry some risk, and between 50 to 100 per 1000 fetuses will be lost due to the second trimester procedure.
Now that the triple or "quad" screen has come into being, the tests can better adjust the fetal DS risk for a given patient, most often below the risk of amniocentesis.
An article in JAMA (soon to be reviewed) has recently ignited controversy regarding the efficacy of the genetic sonogram to more precisely adjust Down syndrome risk so that amniocentesis can be avoided when a risk/benefit mismatch exists. Interestingly, although the authors of this article criticize the benefit of the genetic sonogram, their own data support the reassuring value of a "negative sonogram."
In any case, we have recently found that about 60% of AMA patients seeking prenatal testing with a triple screen and/or a sonogram decline amniocentesis. Hopefully, when the method of fetal cell separation from maternal blood comes to fruition, there will be much less need for amniocentesis. The point is that as some newer techniques become available and older concepts change, fewer invasive techniques will be required.
Percutaneous umbilical blood sampling (PUBS) is a diagnostic technique that emerged in the late 1980s. The original technique for obtaining fetal blood involved the use of an endoscope with which one could draw blood from the umbilical cord under direct visualization. PUBS is less invasive than fetoscopy, but can be tricky to perform and, as is usually the case, the fetal risk is greater than originally reported. The more common indications include rapid karyotyping, diagnosis of fetal anemia from Rh and Kell sensitization, and fetal infections such as Parvovirus. It has also been used to determine fetal blood gas status, for example, in IUGR.
However, for good reason, we are now going through a PUBS "recession." In fact, it is now difficult to find a legitimate reason to do PUBS, and even in busy high- risk centers, there are not enough cases to adequately train perinatal fellows in the performance of this procedure.
Why the paucity of PUBS procedures? Today, through the ability to exclude fetal anemia noninvasively through assessment of doppler waveform analysis of the fetal middle cerebral arteries, amniocentesis is now rarely used in our institution to predict fetal red blood cell breakdown through AOD analysis, and PUBS is only used in cases where there is strong evidence that it would have therapeutic benefit. Rapid karyotyping, previously a PUBS diagnostic staple, can now be accomplished through fluorescent in situ hybridization (FISH) on amniotic fluid cells, enabling clinicians to substitute a less risky procedure for a more invasive one. Since fetal dopplers are so effective at ruling out metabolic acidemia, PUBS is rarely needed in IUGR.
Even with invasive lifesaving fetal therapeutic maneuvers, less invasive measures can help to better select patients whose fetuses would truly benefit from their procedures. For example, in fetal bladder obstruction, it is possible to determine with ultrasound (through the echogenicity of the renal cortex and through electrolyte analysis of aspirated fetal urine) which fetuses are potentially salvageable. Also, although the ultimate surgical technique for fetal diaphragmatic hernia is still up in the air, a rough ultrasound estimate of fetal lung volume can better select fetuses that might possibly benefit from some type of in utero surgery.
In some clinical dilemmas, a more invasive technique may become preferable to a less invasive one, as long it is proven to be more effective. For example, at the moment it is unclear whether endoscopic laser ablation of communicating placental vessels in twin-to-twin transfusion syndrome is of greater therapeutic benefit than repetitive amniocentesis. The latter less invasive measure has been associated with fatal salvage in about 60% of cases, but those investigators using the endoscopic technique are beginning to report a better long- term outcome with laser compared with contemporary data from studies using therapeutic amniocentesis. However, since the populations in the existing studies may not be comparable, the only way to evaluate the best approach would be through randomized clinical trials. After some initial bickering between the two factions, RCTS are being initiated in Europe and the in the United States. Hopefully, these trials will yield usable results.
Where can we go from here? Investigators have been working for more than a decade to separate fetal cells from the maternal circulation, and still the kinks have not been ironed out. When they are, only a few amniocenteses will be performed for only those who really need them. PUBS will undoubtedly be used only where direct access to the fetal circulation is absolutely necessary, such as in intrauterine transfusion, or to deliver a medication directly to the fetus, eg, with a cardiac arrhythmia that is refractory to standard treatment.
"Open" surgical procedures to repair diaphragmatic hernia or to circumvent urethral obstructions are already being replaced by endoscopic techniques, and although the efficacy of in utero repair of spina bifida has definitely not yet been proven, it is likely that the endoscope will ultimately be the vehicle of choice, if legitimate research shows a benefit.
In many clinical situations in obstetrics, the benefit of experience has allowed clinicians to replace the phrase "don’t just stand there, do something" with the concept of "don’t just do something, stand there." In prenatal diagnosis and in many fetal therapeutic ventures "standing there" may not be the best option, but using the least risky (and often glitzy) method to obtain a result is what the art of medicine is all about.