liz@umcp-cs.UUCP (08/31/83)
AMNIOCENTESIS: FACT & FICTION (reprinted without permission from NFP News, No. 3, Spring 1983, Center for Life, Providence Health Foundation, Washington, DC) Amniocentesis, a procedure in which a small amount of amniotic fluid is removed from around the baby for analysis, has become routine for certain pregnant women considered "high risk." Among these are women over 35 and those having a child with either Down's Syndrome or a neural tube defect. Parents in these categories are often traumatized by statistics emphasizing the likelihood of having a handicapped child. For example, a woman at age 35 will be told she has three times the chance of giving birth to a child with Down's Syndrome compared to younger women. The actual statistical likelihood of that occurring is one case out of 360. In other words, her chance of having a child without Down's is greater than 99.7%. A mother who already has a child with a neural tube defect has a 3% chance of having another with that same disorder. In 97% of the cases, however, her baby will be unaffected. According to Dr. Hymie Gordon, a geneticist with the Mayo Clinic, most women receive a greatly exaggerated picture of the likelihood of birth disorders while the risks of amniocentesis are downplayed. He cites a study done by a committee appointed by the Medical Research Council (MRC) of Great Britain which is the only independently-directed, case-controlled study on the hazards of amniocentesis. The results belie the popular presentation of amniocentesis as without risks. In this study women undergoing the procedure experienced a greater than 5% rate of serious complictions in the pregnancy compared to a control group. Hazards included spontaneous abortion, threatened abortion, antepartum hemorrhage (necessitating C section), rupture of membranes, stillbirth, neonatal death, respiratory distress, and musculoskeletal anomolies such as severe clubfoot and congenital dislocation of the hip. Contrast this with the less than 1% risk (even at age 40) of Down's Syndrome or the slightly more than 2% chance of discovering a neural tube defect (closed tube defects will not be detected by amniocentesis). In addition to the physical hazards involved, the usefulness of amniocentesis is also limited by technical problems such as failure to obtain sufficient sample, contamination of the fluid, inability to grow a culture for chromosome analysis, or error in results. In a significant number of cases (Gordon believes over 5% although no adequate statistics exist) repetition of the procedure is required introducing additional risk to the mother and her unborn child. Gordon finds that couples who clearly understand the statistics and the relative risks involved in amniocentesis invariably decline the procedure. It should be noted that the hazards discussed here refer to amniocentesis prior to 20 weeks when pre-natal tests for abnormalities are done. Amniocentesis performed late in pregnancy to determine the maturity of the baby is a much safer procedure. -- -Liz Allen, U of Maryland, College Park MD Usenet: ...!seismo!umcp-cs!liz Arpanet: liz.umcp-cs@Udel-Relay
pat@ih1ap.UUCP (09/01/83)
My wife had an amnio last thursday. In response to the statistics you (they) presented on the net, I must say that the risk/vs./results are somewhat questionable. The primary reason for having this test performed is the detection and possible abortion of a genetically defected child. If the parents decide that they would rather know about the detectable birth defects and accept the risks then it is useful in preventing the birth of these children. However, the consultation we attended showed considerably lower statistics of complication than were posted to the net. Something like less than 1% probability of complications. Secondly, I don't know where the "one in 360" came from but the test is usually recommended for women over 35. The reason is a women 36 years old has a 1 in 125 chance of genetic problems whereas a women of 24 has a 1 in 465 chance. With these statistics the risk of complications can be justified. Patrick A. Fargo BTL -IH
naomi@ubc-medg (Naomi Altman) (09/07/83)
Well, I'm not a geneticist or a doctor, but I work in the department of
medical genetics. I just consulted with a professor in the department whose
specialty is genetic counselling. She handed me a stack of papers on
amniocentesis - complications of pregnancy, post-natal complications, and
legal aspects for doctors involved in counselling.
Estimates of the incidence of Downs' syndrome in women over 35 range
from 2% to 4%. In 1978, 80 types of genetic problems could be identified
with amniocentesis. The number has grown since then.
All of the reports I read indicated no differences in birth complications
or in post-natal development for babies that had been subject to
amniocentesis, and babies of mothers of similar age who had not.
The spontaneous abortion rate after amniocentesis was, in all studies, very
similar to the rate in mothers of similar age who had not undergone amnio -
however, all the reports estimated additional risk of 1% or less (i. e. they
erred on the side of caution.)
The most comprehensive study I have was done in Canada in 1977. (And things
have improved since then.) In 1227 amnio cases, the spontaneous abortion rate
was .2% (this is *extremely* low) and there were mild maternal complications
(such as vaginal leakage) in 3.4% of the cases. There were 7 misdiagnoses in
1227 amnios - of these 2 were wrong sex, and one was a fetus that was already
dead in the womb. 2 normal pregnancies were terminated due to these
misclassifications. As well, two normal pregnancies (one of which was twins)
miscarried due to compications. A 1979 study of 3000 amnios done in the
U.S. had 14 misclassifications, of which 8 were wrong sex.
These two studies also found that larger needle size was implicated with
increased risk of complication. Larger needles are used in order to get a
large enough sample of fluid to analyse. They found that taking 2 samples
with a smaller needle was preferable.
My informant expressed the view that with ultrasound, there was negligible
chance of deforming the fetus with the needle. The literature cites two
cases (out of thousands of amnios). One author felt that ultrasound was
not useful in avoiding this problem. Evidence suggests that ultra-sound
poses no risk to mother or fetus.
A note in the New England Journal of Medicine, 1980 entitled "The Pro-life
bonus of amniocentesis" reports on a survey of 297 mothers who had
undergone amniocentesis. I quote:
"Without the reassurance that amniocentesis would provide, 8.4% of these
pregnancies would not have been undertaken, and another 4.0% would have been
aborted. During the five-year period, positive diagnoses have led to
therapeutic abortions in 7 cases (approximately 2%). There is, therefore,
an apparent "bonus" of 10 pregnancies per 100 that might not have been
completed is amniocentesis had been unavailable to this group of women. "
Naomi Altman
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