PRENATAL DIAGNOSIS, VOL.
12,783-788 (1992)
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY G. CONSTANTINE*, A. F O W L I E ~AND J. PEARSON$ *Good Hope Hospital, Sutton Coldfield. Birmingham B75 7RR. U.K.; ?Derby City Hospital, Derby, U.K.: 1Regional Cytogeneiics Unit. Birmingham Maternity Hospital, Birmingham BI 7 SQH. U.K.
SUMMARY Forty-two women with abnormal ultrasound findings after 27 weeks' gestation underwent a placental biopsy. In 39 cases, a karyotype was obtained from a direct preparation within 48 h, five abnormal karyotypes being detected (four trisomies and a triploidy). One confirmed placental mosaic was also detected. In one case, a small terminal deletion of chromosome 7 was not detected at the time due to the quality of the preparation. A karyotype can be obtained from a direct preparation in the third trimester in over 90 per cent of cases, the quality of the preparation allowing the reliable detection of abnormalities of chromosome number. We believe that this technique may be usefully, reliably, and safely employed in the third trimester of pregnancy by those with an interest in antenatal ultrasound diagnosis who do not have immediate access to a cytogenetics laboratory and who feel that cordocentesis is inappropriate for their situation. KEY WORDS
Placental biopsy Antenatal diagnosis
INTRODUCTION Many fetal abnormalities are associated with an abnormal karyotype, and if found on a routine scan a karyotyping procedure is indicated. Similarly, growth retardation in the third trimester may also be associated with karyotype abnormalities, particularly trisomies and triploidy. At this stage in the pregnancy, rapid results are important as the finding of an abnormal karyotype may influence obstetric management. Possible karyotyping procedures include amniocentesis, placental biopsy, or fetal blood sampling. Each has advantages and disadvantages. Amniocentesis is widely available, safe, and reliable, but unless specialist techniques are employed (Claussen el al., 1986) results are not available for 3-4 weeks. Cordocentesis gives rapid results, but demands a higher level of operator skill and may not be appropriate for all centres (Whittle, 1989). Placental biopsy, an extension of first-trimester chorionic villus sampling (CVS), has been advocated as a safe, easily learnt, and widely applicable technique which gives rapid and reliable results (Nicolaides et al., 1986a; Lilford et al., 1987). Although widely practised in the second trimester, its use after 27 weeks is less well documented. We describe our experience of placental biopsy after 27 weeks' gestation in 42 women. Addressee for correspondence: Dr G. Constantine, Good Hope Hospital, Sutton Coldfield, Birmingham B75 7RR, U.K.
0197-385 1/92/100783-06$08.00 0 1992 by John Wiley & Sons, Ltd.
Received 15 April 1991 Accepted 24 January 1992
784
G . CONSTANTINE E T A L .
Table 1. Breakdown of procedures at each gestation Gestation (weeks)
Number
Abnormal Failures
28 29 30
31 32
33 34 35
36
Totals
3 I
9
3
5 1
6
42 5 3
3 1
2
7 2 1
4 1
1
METHODS Placental biopsy was performed in 42 cases from mid-1987 onwards, where a rapid karyotype was thought appropriate. All women had a fetus with an anomaly noted on ultrasound (75 per cent single): hydrops, severe growth retardation, or abnormalities of liquor volume. In these women, the placenta was localized using a 3.5 MHz linear array transducer (Accuson). The skin was cleaned with alcohol, and 1 per cent lignocaine infiltrated at the intended site of insertion. An 18 G spinal needle was rinsed with heparin and inserted into the placenta under ultrasound guidance. Placental villi were then collected by continuous suction combined with a rotating and gentle up and down movement of the needle. In the majority of cases, suction was applied with a 20 ml syringe containing 5 ml of heparinized culture medium, but in the latter part of the series an electric suction pump was employed which was set to give a similar vacuum, and with a hole in the connection (occluded by the operator’s finger) to allow rapid release of suction if needed. The resulting samples were immediately inspected to confirm the presence of sufficient villi, a minimum of 10 mg of villi being the aim. Direct chromosome preparations were made using the same standard techniques employed for first-trimester CVS (Simoni et al., 1983; Flori et al., 1985). Samples were collected into RPMI and heparin and incubated in RPMI + 10 per cent calf serum. Both direct preparations and 24 h cultures were employed, slides being G-banded using standard techniques. RESULTS Table 1 shows the numbers performed at differing gestations, together with the abnormalities found and karyotyping failures. All attempts are included. Where the chromosomal analysis failed, only 5 mg or less of villi had been obtained. Five of the karyotypes proved abnormal, including one trisomy 21, two trisomy 13, one trisomy 18, and one 69,XXX. In addition, one case showed a mosaic confined to the placental tissue, a blood sample at birth confirming a normal karyotype. One fetus was noted to be severely growth retarded with oligohydramnios at 30 weeks’ gestation. A placental biopsy was performed which showed a 46,XX karyotype, a long-term culture and amniocentesis not being performed. At birth, the baby appeared severely growth retarded and also proved to have low-set ears, a cleft lip and palate, a short neck, coarctation of the aorta, and hepatic fibrosis. A postnatal karyotype showed a small terminal deletion of the long arm of chromosome 7, i.e.,
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY
785
46,XX,de1(7)(q34). Subsequent re-examination of the placental biopsy slides showed the deletion to be present, but that it had been missed because of a suboptimal preparation. With such a heterogeneous group of high-risk patients, many of whom underwent premature delivery, possible effects of the procedure on the pregnancy are difficult to evaluate. No obvious connection was, however, apparent from a study of the notes.
DISCUSSION Many studies have shown the high incidence of abnormal karyotypes, particularly trisomies, in women who present with certain fetal abnormalities (Nicolaides et al., 1986b; Platt et al., 1986; Palmer et al., 1987; Williamson et al., 1987; Wladimiroff et al., 1988). Whilst based on variable and selected populations, incidences of between 19 and 35 per cent are quoted. A knowledge of such associations is therefore vital to all who perform detailed ultrasound scans, who should also be in a position to perform an immediate karyotyping procedure. Traditionally, this has involved amniocentesis but this may be inappropriate when rapid information is required and specialist micro-pipetting techniques are not available. Women found to have a fetal abnormality on ultrasound value rapid clarification of the problem, whilst in the third trimester the finding of a chromosomal abnormality in a woman with an abnormal or growth-retarded fetus may influence obstetric management. Placental biopsy with karyotyping on a direct preparation appears the most widely applicable alternative to amniocentesis in such cases. Doubts have, however, been expressed as to the reliability of the cytogenetic techniques at this gestation due to the declining mitotic index. Several large series have been reported which show that chorionic villus biopsy may safely be performed as an alternative to amniocentesis in the second trimester. Most are in women at risk of a chromosomal abnormality because of their age or past history (Pijpers et al., 1988; Wolstenholme et al., 1989; Chieri and Aldini, 1989). These and other series have reported smaller numbers performed in the second and third trimesters in response to abnormal ultrasound findings (Nicolaides et al., 1986b; Basaran et al., 1988;Hogdall et al., 1988; Hentemann et al., 1989; Saura et al., 1989; Wolstenholme et al., 1989). One paper reports a total of 70 cases in the third trimester (Holzgreve et al., 1990a), whilst another reports these plus another 71 from a total of 24 centres world-wide (Holzgreve et al., 1990b). Unfortunately, in the latter case these are presented amongst 2058 cases performed after 12 weeks, the complications and outcomes being combined. Other published series appear to be heavily skewed towards gestations of under 30 weeks, the maximum over 30 weeks’ gestation being 1 1 cases (Saura et al., 1989), again combined in the above multicentre survey. We failed to obtain a karyotype from a direct preparation in three cases (7.14 per cent), in all of which only 5 mg of villi had been obtained. Failure rates quoted in other series for second- and third-trimester placental biopsy range from 0 to 9.5 per cent, the failure rate appearing to rise with gestational age. Six biopsies were attempted at 36 weeks’ gestation, five yielding a karyotype. There is a well-known
786
G. CONSTANTINE ETAL.
Table 2. False-negative results reported after second- and third-trimester placental biopsy Series Wolstenholme er 01. (1989) Leschot et al. (1988) Saura et af. (1989) Eiben et af.(1988) Wirtz et a!. (1988) This series*
Placental karyotype
Actual karyotype
46,XY 46,XX 46,XX 46,XY 46,XY 46,XX
45,X/46,XYmosaic 46,XX/47,XX,+ 18 mosaic 46,XY 46,XY,del(4)(p15.2) 47,XY + 18 46,XX,de1(7)(q34)
*This case is, in fact, an example of a missed abnormality due to poor quality preparations, but for clinical purposes amounted to a false negative.
potential in first-trimester CVS for false-positive results from placental mosaicism and genuine false-negative results (Simoni et al., 1986; Leschot et al., 1987; Callen et al., 1988; Schwinger et af., 1989). This is not confined to the first trimester, several false-negative diagnoses having been made in later pregnancy (Table 2). We found one placental mosaic, and one false-negative result where a small deletion was missed in an abnormal fetus. Taken overall, our results show that a karyotype can be obtained within 48 h from a direct preparation in the third trimester in over 90 per cent of cases, greater if at least 10 mg of tissue is provided. The quality of the preparation allows the reliable detection of abnormalities of chromosome number, although caution is needed if deletions or translocations are suspected. In view of this, and the possibility of failure to obtain a karyotype from a direct preparation, there is a n argument in favour of performing an amniocentesis at the same time as a back-up. The technique of placental biopsy is simple and easy to learn for those with an interest in antenatal scanning, whilst the extra equipment required is minimal, cheap, and readily available. All reported series of placental biopsy, however, appear to be from large obstetric centres which have close links with cytogenetic departments. Practical considerations need to be taken into account if this technique is to be widely employed by obstetricians geographically separated from such a unit. Quoted minimal weights of villi necessary for karyotyping are > 2 m g (Wolstenholme et al., 1989), 5 mg (Saura et al., I989), and 10 mg (Pijpers rt ul., 1988), this being estimated by immediate microscopy and separation of villi into culture medium. In an isolated unit, specialist help may not be immediately available. In such a situation, suitable heparinized culture/transport media can be bought or supplied by a regional cytogenetics unit and kept deep-frozen unit required, whilst the likely presence of villi in a sample can be confirmed in a Petri dish or sample tube using low magnification or even the naked eye. The sealed collection tube must then be transported to the cytogenetics laboratory as soon as possible. Since completing the above series, a further three biopsies have been successfully performed by one of us utilizing this technique. We believe that placental biopsy may be usefully employed in the second and third trimesters of pregnancy by those with an interest in antenatal ultrasound diagnosis
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY
787
who do not have immediate access to a cytogenetics laboratory. Further study in this situation is warranted.
REFERENCES Basaran, S., Miny, P., Pawlowitzki, I., Horst, J., Holzgreve, W. (1988). Rapid karotyping for prenatal diagnosis in the second and third trimesters of pregnancy, Prenat. Diagn., 8, 3 15-320. Callen, D.F., Korban, G . , Dawson, G., Gugasyan, L., Krumins, E.J., Eichenbaum, S., Petrass, J., Purvis Smith, S., Smith, A., DenDulk, G . (1988). Extraembryonic/fetal karyotypic discordance during diagnostic chorionic villus sampling. Prenat. Diagn., 8, 453-460. Chieri, P.R., Aldini, A.J.R. (1989). Feasibility of placental biopsy in the second trimester for fetal diagnosis, Am. J. Obstet. Gynecol., 160,581-583. Claussen, U., Klein, R., Schmidt, M. (1986). A pipette method for rapid karyotyping, Prenat. Diugn.,6,401-408. Eiben, B., Leipoldt, M., Schubbe, I., Ulbrich, R., Hansmann, R. (1988). Partial deletion of4p in fetal cells not present in chorionic villi, Clin. Genet., 33,49-52. Flori, E., Nisand, I., Flori, J., Dellenbach, P., Ruch, J.V. (1985). Direct fetal chromosome studies from chorionic villi, Prenat. Diagn., 5,287-289. Hentemann, M., Rauskolb, R., Ulbrich, R., Bartels, I. (1989). Abnormal pregnancy sonogram and chromosomal anomalies: four years experience with rapid karyotyping, Prenat. Diagn., 9,605-612. Hogdall, C.K., Doran, T.A., Shime, J., Wilson, S., Teshima, I. (1988). Transabdominal chorionic villus sampling in the second trimester, Am. J . Obstet. Gynecol., 158,345-349. Holzgreve, W., Miny, P., Gerlach, B., Westendorp, A,, Ahlert, D., Horst, J. (1990a). Benefits of placental biopsies for rapid karyotyping in the second and third trimesters (late chorionic villous sampling) in high risk pregnancies, Am. J . Obstet. Gynecol., 162, 1188-1 192. Holzgreve, W., Miny, P., Schloo, R. and participants of the ‘Late CVS’ Registry (I990b). ‘Late CVS’ international registry compilation of data from 24 centres, Prenat. Diagn., 10, 159-167. Leschot, N.J., Wolf, H., Verjaal, M., Prooijen-Knegt, I.C., DeBoer, E. G., Kanhai, H.H., Christiaens, G.C.M.L. (1987). Chorionic villus sampling: cytogenetic and clinical findings in 500 pregnancies, Br. Med. J., 295,407-410. Leschot, N.J., Wolf, H., Weenink, G.H. (1988). False negative findings at third trimester chorionic villus sampling (CVS), Cfin. Genet., 34,204-205. Lilford, R.J., Linton, G., Irving, H.C., Mason, M.K. (1987). Transabdominal chorionic villus biopsy; 100 consecutive cases, Lancet, I, 1415-1416. Nicolaides, K.H., Rodeck, C.H., Gosden, C.M. (1986a). Rapid karyotyping in non-lethal fetal malformations, Lancet, 1,283-286. Nicolaides, K., Soothill, P.W., Rodeck, C.H., Warren, R.C. (1986b). Why confine chorionic villous biopsy to the first trimester?, Lancet, 1,543-544. Palmer, C.G., Miles, J.H., Howard, P.P.N., Magenis, R.E., Patil, S. (1987). Fetal karyotype following ascertainment of fetal anomalies by ultrasound, Prenat. Diagn., 7, 55 1-555. Pijpers, L., Jahoda, M.G.J., Reuss, A., Wladimiroff, J., Sachs, E. (1988). Transabdominal chorionic villus biopsy in second and third trimesters of pregnancy to determine fetal karyotype, Br. Med. J., 297,822-823. Platt, L.D., DeVore, G.R., Lopez, E., Herbert, W., Falk, R. (1986). Role of amniocentesis in ultrasound detected fetal malformations, Ohstet. Gynecol., 68, 153-1 55. Saura, A,, Longy, M., Horovitz, J., Vergnaud, A,, Grison, 0. (1989). Direct chromosome analysis in the second and third trimesters by placental biopsy in 30 pregnancies, Br. J . Obstet. Gynaecol., 96, 1215-1218. Schwingcr, E., Seidl, E., Klink, F., Rehder, H. (1989). Chromosome mosaicism of the placenta: a cause of developmental failure of the fetus, Prenat. Diagn., 9,639-648.
788
G. CONSTANTINE ET AL.
Simoni, G., Brambati, B., Danesino, C . , Rosella, F.,Terzoli, G.L., Ferrari, M., Fraccaro, M. (1983). Efficient direct chromosome analyses and enzyme determinations from chorionic villi samples in the first trimester of pregnancy, Hum. Genet., 63,349-357. Simoni, G . , Gimelli, G., Cuoco, C., Romitti, L., Terzoli, G., Guerneri, S., Rossella, F., Pescetto, L., Pezzolo, A., Porta, S. (1986). First trimester fetal karyotyping: one thousand diagnoses, Hum. Genet., 72,203-209. Whittle, M.J. (1989). Br. J . Obstet. Gynaecol., 96,262-265. Williamson, R., Weiner, C.P., Patil, S., Benda, J., Varner, M.W. (1987).Abnormal pregnancy sonogram: selective indication for fetal karyotype, Obstet. Gynecol., 69, 15-20. Wladimiroff, J., Sachs, E.S., Reuss, A., Stewart, P.A., Pijpers, L., Nierrneijer, M.F. (1988). Prenatal diagnosis of chromosome abnormalities in the presence of fetal structural defects, Am. J . Med. Genet., 29,289-291. Wolstenholme, J., Hoogfwerf, A.M., Sheridan, H., Maher, E.J., Little, D.J. (1989). Practical experience using transabdominal chorionic villus biopsies taken after 16 weeks’ gestation for rapid prenatal diagnosis of chromosomal abnormalities, Prenat. Diagn., 9,357-359.
12,783-788 (1992)
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY G. CONSTANTINE*, A. F O W L I E ~AND J. PEARSON$ *Good Hope Hospital, Sutton Coldfield. Birmingham B75 7RR. U.K.; ?Derby City Hospital, Derby, U.K.: 1Regional Cytogeneiics Unit. Birmingham Maternity Hospital, Birmingham BI 7 SQH. U.K.
SUMMARY Forty-two women with abnormal ultrasound findings after 27 weeks' gestation underwent a placental biopsy. In 39 cases, a karyotype was obtained from a direct preparation within 48 h, five abnormal karyotypes being detected (four trisomies and a triploidy). One confirmed placental mosaic was also detected. In one case, a small terminal deletion of chromosome 7 was not detected at the time due to the quality of the preparation. A karyotype can be obtained from a direct preparation in the third trimester in over 90 per cent of cases, the quality of the preparation allowing the reliable detection of abnormalities of chromosome number. We believe that this technique may be usefully, reliably, and safely employed in the third trimester of pregnancy by those with an interest in antenatal ultrasound diagnosis who do not have immediate access to a cytogenetics laboratory and who feel that cordocentesis is inappropriate for their situation. KEY WORDS
Placental biopsy Antenatal diagnosis
INTRODUCTION Many fetal abnormalities are associated with an abnormal karyotype, and if found on a routine scan a karyotyping procedure is indicated. Similarly, growth retardation in the third trimester may also be associated with karyotype abnormalities, particularly trisomies and triploidy. At this stage in the pregnancy, rapid results are important as the finding of an abnormal karyotype may influence obstetric management. Possible karyotyping procedures include amniocentesis, placental biopsy, or fetal blood sampling. Each has advantages and disadvantages. Amniocentesis is widely available, safe, and reliable, but unless specialist techniques are employed (Claussen el al., 1986) results are not available for 3-4 weeks. Cordocentesis gives rapid results, but demands a higher level of operator skill and may not be appropriate for all centres (Whittle, 1989). Placental biopsy, an extension of first-trimester chorionic villus sampling (CVS), has been advocated as a safe, easily learnt, and widely applicable technique which gives rapid and reliable results (Nicolaides et al., 1986a; Lilford et al., 1987). Although widely practised in the second trimester, its use after 27 weeks is less well documented. We describe our experience of placental biopsy after 27 weeks' gestation in 42 women. Addressee for correspondence: Dr G. Constantine, Good Hope Hospital, Sutton Coldfield, Birmingham B75 7RR, U.K.
0197-385 1/92/100783-06$08.00 0 1992 by John Wiley & Sons, Ltd.
Received 15 April 1991 Accepted 24 January 1992
784
G . CONSTANTINE E T A L .
Table 1. Breakdown of procedures at each gestation Gestation (weeks)
Number
Abnormal Failures
28 29 30
31 32
33 34 35
36
Totals
3 I
9
3
5 1
6
42 5 3
3 1
2
7 2 1
4 1
1
METHODS Placental biopsy was performed in 42 cases from mid-1987 onwards, where a rapid karyotype was thought appropriate. All women had a fetus with an anomaly noted on ultrasound (75 per cent single): hydrops, severe growth retardation, or abnormalities of liquor volume. In these women, the placenta was localized using a 3.5 MHz linear array transducer (Accuson). The skin was cleaned with alcohol, and 1 per cent lignocaine infiltrated at the intended site of insertion. An 18 G spinal needle was rinsed with heparin and inserted into the placenta under ultrasound guidance. Placental villi were then collected by continuous suction combined with a rotating and gentle up and down movement of the needle. In the majority of cases, suction was applied with a 20 ml syringe containing 5 ml of heparinized culture medium, but in the latter part of the series an electric suction pump was employed which was set to give a similar vacuum, and with a hole in the connection (occluded by the operator’s finger) to allow rapid release of suction if needed. The resulting samples were immediately inspected to confirm the presence of sufficient villi, a minimum of 10 mg of villi being the aim. Direct chromosome preparations were made using the same standard techniques employed for first-trimester CVS (Simoni et al., 1983; Flori et al., 1985). Samples were collected into RPMI and heparin and incubated in RPMI + 10 per cent calf serum. Both direct preparations and 24 h cultures were employed, slides being G-banded using standard techniques. RESULTS Table 1 shows the numbers performed at differing gestations, together with the abnormalities found and karyotyping failures. All attempts are included. Where the chromosomal analysis failed, only 5 mg or less of villi had been obtained. Five of the karyotypes proved abnormal, including one trisomy 21, two trisomy 13, one trisomy 18, and one 69,XXX. In addition, one case showed a mosaic confined to the placental tissue, a blood sample at birth confirming a normal karyotype. One fetus was noted to be severely growth retarded with oligohydramnios at 30 weeks’ gestation. A placental biopsy was performed which showed a 46,XX karyotype, a long-term culture and amniocentesis not being performed. At birth, the baby appeared severely growth retarded and also proved to have low-set ears, a cleft lip and palate, a short neck, coarctation of the aorta, and hepatic fibrosis. A postnatal karyotype showed a small terminal deletion of the long arm of chromosome 7, i.e.,
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY
785
46,XX,de1(7)(q34). Subsequent re-examination of the placental biopsy slides showed the deletion to be present, but that it had been missed because of a suboptimal preparation. With such a heterogeneous group of high-risk patients, many of whom underwent premature delivery, possible effects of the procedure on the pregnancy are difficult to evaluate. No obvious connection was, however, apparent from a study of the notes.
DISCUSSION Many studies have shown the high incidence of abnormal karyotypes, particularly trisomies, in women who present with certain fetal abnormalities (Nicolaides et al., 1986b; Platt et al., 1986; Palmer et al., 1987; Williamson et al., 1987; Wladimiroff et al., 1988). Whilst based on variable and selected populations, incidences of between 19 and 35 per cent are quoted. A knowledge of such associations is therefore vital to all who perform detailed ultrasound scans, who should also be in a position to perform an immediate karyotyping procedure. Traditionally, this has involved amniocentesis but this may be inappropriate when rapid information is required and specialist micro-pipetting techniques are not available. Women found to have a fetal abnormality on ultrasound value rapid clarification of the problem, whilst in the third trimester the finding of a chromosomal abnormality in a woman with an abnormal or growth-retarded fetus may influence obstetric management. Placental biopsy with karyotyping on a direct preparation appears the most widely applicable alternative to amniocentesis in such cases. Doubts have, however, been expressed as to the reliability of the cytogenetic techniques at this gestation due to the declining mitotic index. Several large series have been reported which show that chorionic villus biopsy may safely be performed as an alternative to amniocentesis in the second trimester. Most are in women at risk of a chromosomal abnormality because of their age or past history (Pijpers et al., 1988; Wolstenholme et al., 1989; Chieri and Aldini, 1989). These and other series have reported smaller numbers performed in the second and third trimesters in response to abnormal ultrasound findings (Nicolaides et al., 1986b; Basaran et al., 1988;Hogdall et al., 1988; Hentemann et al., 1989; Saura et al., 1989; Wolstenholme et al., 1989). One paper reports a total of 70 cases in the third trimester (Holzgreve et al., 1990a), whilst another reports these plus another 71 from a total of 24 centres world-wide (Holzgreve et al., 1990b). Unfortunately, in the latter case these are presented amongst 2058 cases performed after 12 weeks, the complications and outcomes being combined. Other published series appear to be heavily skewed towards gestations of under 30 weeks, the maximum over 30 weeks’ gestation being 1 1 cases (Saura et al., 1989), again combined in the above multicentre survey. We failed to obtain a karyotype from a direct preparation in three cases (7.14 per cent), in all of which only 5 mg of villi had been obtained. Failure rates quoted in other series for second- and third-trimester placental biopsy range from 0 to 9.5 per cent, the failure rate appearing to rise with gestational age. Six biopsies were attempted at 36 weeks’ gestation, five yielding a karyotype. There is a well-known
786
G. CONSTANTINE ETAL.
Table 2. False-negative results reported after second- and third-trimester placental biopsy Series Wolstenholme er 01. (1989) Leschot et al. (1988) Saura et af. (1989) Eiben et af.(1988) Wirtz et a!. (1988) This series*
Placental karyotype
Actual karyotype
46,XY 46,XX 46,XX 46,XY 46,XY 46,XX
45,X/46,XYmosaic 46,XX/47,XX,+ 18 mosaic 46,XY 46,XY,del(4)(p15.2) 47,XY + 18 46,XX,de1(7)(q34)
*This case is, in fact, an example of a missed abnormality due to poor quality preparations, but for clinical purposes amounted to a false negative.
potential in first-trimester CVS for false-positive results from placental mosaicism and genuine false-negative results (Simoni et al., 1986; Leschot et al., 1987; Callen et al., 1988; Schwinger et af., 1989). This is not confined to the first trimester, several false-negative diagnoses having been made in later pregnancy (Table 2). We found one placental mosaic, and one false-negative result where a small deletion was missed in an abnormal fetus. Taken overall, our results show that a karyotype can be obtained within 48 h from a direct preparation in the third trimester in over 90 per cent of cases, greater if at least 10 mg of tissue is provided. The quality of the preparation allows the reliable detection of abnormalities of chromosome number, although caution is needed if deletions or translocations are suspected. In view of this, and the possibility of failure to obtain a karyotype from a direct preparation, there is a n argument in favour of performing an amniocentesis at the same time as a back-up. The technique of placental biopsy is simple and easy to learn for those with an interest in antenatal scanning, whilst the extra equipment required is minimal, cheap, and readily available. All reported series of placental biopsy, however, appear to be from large obstetric centres which have close links with cytogenetic departments. Practical considerations need to be taken into account if this technique is to be widely employed by obstetricians geographically separated from such a unit. Quoted minimal weights of villi necessary for karyotyping are > 2 m g (Wolstenholme et al., 1989), 5 mg (Saura et al., I989), and 10 mg (Pijpers rt ul., 1988), this being estimated by immediate microscopy and separation of villi into culture medium. In an isolated unit, specialist help may not be immediately available. In such a situation, suitable heparinized culture/transport media can be bought or supplied by a regional cytogenetics unit and kept deep-frozen unit required, whilst the likely presence of villi in a sample can be confirmed in a Petri dish or sample tube using low magnification or even the naked eye. The sealed collection tube must then be transported to the cytogenetics laboratory as soon as possible. Since completing the above series, a further three biopsies have been successfully performed by one of us utilizing this technique. We believe that placental biopsy may be usefully employed in the second and third trimesters of pregnancy by those with an interest in antenatal ultrasound diagnosis
PLACENTAL BIOPSY IN THE THIRD TRIMESTER OF PREGNANCY
787
who do not have immediate access to a cytogenetics laboratory. Further study in this situation is warranted.
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