4.3 LOS EFECTOS DEL CLIMA ORGANIZACIONAL EN LOS TRABAJADORES DE
4.3.1 Comunicación
The follow ing outcom e d ata can only be considered a g u id e rath e r th an definitive results, as the sam ple size is too sm all to d raw final conclusions about the com parative safety of the tw o procedures. The outcom e for all 650 cases undergoing first trim ester fetal karyotyping is show n in Table 2.5.
Early amniocentesis n=324 (%)
Chorion villus sam pling n=326 (%)
LB 298 (92.0) 306 (93.8)
NN D 1 (0.3) -
lU D /SA 17 (5.2) 4 (1.2)
TOP 8 (2.5) 16» (5.0)
*in two cases TOP was because of anencephaly and spina bifida respectively Table 2.5 Outcome of 650 first trim ester procedures for fetal karyotype, illustrating num ber of livebirths (LB), neonatal deaths (NND), intrauterine
deaths / spontaneous abortions (lU D /SA ) and term ination of pregnancy (TOP) for early am niocentesis and chorion villus sam pling.
These d ata illustrate a sim ilar livebirth rate for the tw o procedures, how ever th ere a p p ea r to be m ore sp o n tan eo u s fetal losses (lU D /S A ) in the early am niocentesis group (5.2% versus 1.2%). W hilst the n u m b er of fetal losses are sm all, especially in the CVS group, the difference m ay illustrate a trend
toward a higher complication rate with early amniocentesis.
Case Procedure Gestation of procedure Outcome Gestation of fetal loss 1 EA 12.7 lUD 13 2 EA 12.6 lUD 14 3 EA 11.3 lUD* 12 4 EA 10.9 lUD 29 5 EA 13.9 lUD 31 6 EA 11.1 lUD 26 7 EA 11.6 lUD 13 8 EA 11.3 SA 13 9 EA 12.6 SA 16 10 EA 11.7 SA 14 11 EA 11.4 SA 13 12 EA 11.4 SA 13 13 EA 10.7 SA 12 14 EA 12.3 SA 13 15 EA 10.6 SA 13 16 EA 12.4 SA 17 17 EA 11.0 SA 13 18 CVS 10.6 lUD 40 19 CVS 10.7 SA*^ 11 20 CVS 11.0 SA 14 21 CVS 10.4 SA 16 22 EA 12.4 N N D 28 *Chorioamniitis
Table 2.6 Gestational age at w hich early am niocentesis (EA) and chorion villus sam pling (CVS) w as perform ed and at w hich fetal loss by spontaneous
abortion (SA), intrauterine death (lUD) or neonatal death (NND) occurred.
The fetal losses occurred a m ean of 31 days (range 1-127 days) after early am niocentesis and 85 days (range 2-275 days) after CVS. The m ean gestation
of the procedure w hich resulted in fetal loss w as 11.7 weeks (range 10.6-13.9 w eeks) for early am niocentesis an d 10.6 w eeks (range 10.4-11.0 w eeks) for CVS. Infection w as identified as the cause in one case for each g roup (table 2.6; cases 3 and 19). There was one neonatal death in the early am niocentesis g ro u p (table 2.6; case 22), w hich occu rred a t 28 w eeks g estatio n after em ergency caesarean section for an tep artu m h aem o rrh ag e an d one of the intrauterine deaths in the CVS group occurred at term (table 2.6; case 18).
The fetal loss rates are an unexpected finding, as the prelim inary results from uncontrolled trials (section 1.4.2) suggest that early am niocentesis is as safe as late am niocentesis, w hich has been sh o w n to be safer th a n CVS (MRC E u ro p ean trial 1991). Thus a h ig h er fetal loss rate w o u ld be expected follow ing CVS. P erhaps the reason for this p arad o x is explained b y the design of this trial, w hich com pared the tw o procedures being perform ed in the sam e w ay by experienced operators, rath er th an a variety of techniques perform ed in different centres by operators of varying skill, as in the MRC E uropean trial (1991). This trial w as designed to show the in h eren t risk of sam pling the tw o tissues (am niotic fluid versus chorionic villi) an d if this tren d is confirm ed on larger num bers it will indicate th at sam pling chorionic villi is the safer pro ced u re. H ow ever other factors, such as cytogenetic accuracy, fetal m o rb id ity (Firth et al 1991), cost an d lab o rato ry expertise (Association of Clinical Cytogeneticists W orking Party 1987) will have to be considered before ad o p tin g one procedure in preference to th e other. These will only be established w ith the resu lt of a large p rospective random ised trial of early amniocentesis an d CVS.
Feasibility of early amniocentesis: summary
1. The num ber of cells in am niotic fluid increases w ith advancing gestation, b u t the proportion of live cells is greater in early pregnancy. As a result, the nu m b er of live cells at 10-14 w eeks' gestation is sim ilar to the num ber at IS IS w eeks' gestation.
2. There is an exponential increase in the num ber of d ead cells in am niotic fluid from 14 w eeks gestation onw ards. This m ay be d u e to release of dead cells from the urinary tract of the fetus, as the fetus starts to pass urine. Only by characterising cells by their site of origin will this become apparent.
3. The p ilo t stu d y perfo rm ed on pregnancies p rio r elective term in atio n dem onstrates th at am niocentesis beyond a fetal CRL of 37 m m is likely to be as successful as second trim ester amniocentesis. Before this tim e the culture failure rate is unacceptably high.
4. To establish the technical aspects of early am niocentesis it is m ost relevant to com pare it to the only other early prenatal test CVS. The gestational range for com parison considered useful is 10-14 weeks'.
5. In a random ised com parison of sim ilar groups a sam ple w as successfully obtained a t the first attem p t in 98.8% cases for early am niocentesis an d in 97.2% cases for CVS; cell culture and chrom osom al analysis w as successful in 98.1% an d 99.4% cases respectively.
6. Two needle insertions w ere req u ired m ore frequently w ith CVS (2.8% cases) th an w ith early am niocentesis (1.2% cases). There w as no significant
difference betw een the tests for the tim e the needle w as in the uterus (CVS 50 seconds, early amniocentesis 45 seconds; p=0.49).
7. C ytogenetic results revealed a norm al m ale an d norm al fem ale in 52% an d 48% cases respectively. A bnorm al k ary o ty p e w as diag n o sed in 3.8% cases, the com m onest abnorm ality w as autosom al aneuploidy.
8. There w ere no mosaic, pseudom osaic or m aternal cell contam inations in the early am niocentesis group, w hereas there w as one confined placental m osaic, one m aternal cell contam ination and three tru e m osaics in the CVS group. If this d isp arity rem ains w hen larger n u m b ers are stu d ied it will represent a major advantage of early am niocentesis over CVS.
9. Prelim inary results on pregnancy outcom e suggest th at the livebirth rate for early amniocentesis is similar to th at of CVS (92% versus 93.8%), b u t that early amniocentesis carries a higher fetal loss rate (5.2% versus 1.2%). This is yet to be confirmed by a larger study.