CURRENT INVESTIGATION
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Fetal blood sampling in midtrimester pregnancies MITCHELL YUET
S. W.
MARVEEN San Francisco,
GOLBUS,
KAN,
M.D.
M.D.
NAGLICH-CRAIG,
R.D.M.S.
California
Sonographically directed placental aspiration has been investigated as a method for obtaining fetal erythrocytes. The technigue is generally successful and the fetal red cells a,re genera,lly usable for the prena.tal dia,gnosis of the hemoglobinopathies.
THE PRENATAL diagnosis of genetic defects has been a major step forward for both obstetrics and human genetics. Amniotic fluid cells have been used to obtain information about the fetus, and the information available has been limited to that normally expressed in these cells. The prenatal diagnosis of a hemoglobinopathy or of a red cell enzymatic deficiency requires the ability to obtain fetal red cells. This has been attempted with the use of fetoscopy-directed aspiration’, 2 and, in the case of an anterior placenta demonstrated by ultrasound, “blind’ aspiration.3 We have sought to define a method for obtaining fetal
From the Departments of Obstetrics and Gynecology, Medicine, Clinical Pathology and Laboratory Medicine, and Radiology, University of California San Francisco. Supported in part by grants from the National Foundation-March of Dimes, National Institutes Health, and the John A. Hartford Foundation.
of
Reprint requests: Dr. Mitchell Golbus, Department of Obstetrics and Gynecology, School of Medicine, Universig of Cala@zia San Francisco, San Fran&co, California 94143.
erythrocytes in a mixed fetal-maternal sample by sonographically directed placental aspiration regardless of placental location.
Methods The 28 patients in this study either were having elective pregnancy termination for socioeconomic indications or because of a chromosomally abnormal fetus or were referred to our program for prenatal diagnosis of a hemoglobinopathy. All patients gave expressed informed consent for the procedure as per a protocol approved by the University of California San Francisco Committee on Human Experimentation. The patients undergoing pregnancy terminations had a sonographic placental localization with a full bladder and again after voiding. Bladder emptying was found to move the placental site 3 to 5 cm. caudally. In the case of a posterior placenta, the 20 gauge, 3 ‘/ inch, disposable spinal needle was introduced into the amniotic sac. Fluid aspiration and needle advancement were alternated until the needle bevel was against the fetal surface of the placental plate as indicated by a lack
March Am. J. Obstet.
654 Golbus, Kan, and Naglich-Craig
Table I. Fetal blood aspiration
samples obtained
by placental
of a hetnoglobinopathy, homozygously affected, nated. and the prenatal
1.5, 1976 Gynrcol.
four fetuses were found to Rc the pregnancira were termidiagnosis \vas ( onfirmed
Comment O-I
6
2-1 5-10 7s-ho 15”5
2 4 3
21.4 7.1 14.3 10.7
of amniotic fluid return. The needle was inserted 2 to 4 mm. further for blood aspiration. A series of five or six samples was taken as the needle was withdrawn back into the amniotic sac, and a sample of the amniotic fluid in the immediate area of the placental puncture was included. One or two insertions into the placenta provided the 5 or 6 samples which need contain onl! 50 to 100 ~1 of blood mixed in amniotic fluid. A set of 5 or 6 samples was considered as one attempt at placental aspiration. In the case of an anterior placenta. the placenta was traversed by the 20 gauge needle until amniotic Huid was obtained. The procedure was similar, but the needle was withdrawn until it reached the placental plate and then was withdrawn 2 to 4 mm. further, into the fetal surface of the placenta. Women having a therapeutic abortion had only one attempt at placental aspiration, and then 40 mg. of prostaglandin F,a was instilled in the amniotic sac to induce the abortion. Patients referred for the prenatal diagnosis of a hemoglobinopathy had multiple atempts, if necessary, to obtain fetal red cells. The presence of fetal erythrocytes was determined by analysis of red cell volume by a Coulter counter since the fetal cell volume is larger than that of adult cells.” In the last half of the study, the percentage of fetal cells was verified by Kleihauer-Betke stains of smears from the same samples.
Results ‘Fhe percentage of fetal erythrocytes in placental aspirates is given in Table I. Samples from the nine posterior placentas had 2 to IO0 per cent fetal cells. and in no case was a second attempt necessary. Eleven of 16 (69 per cent) anterior placentas yielded samples of 2 per cent or more fetal red cells, but in two patients this required three attempts each. Two of three lateral placentas provided samples with 22 and 75 per cent fetal cells. Of the eight patients referred for prenatal diagnosis
For prenatal diagnosis of the hemoglobinopathies. a mixture of fetal and maternal blood can be used and, by concentrating fetal cells with differential agglutination with the use of anti-i serum, as little as 2 per cent fetal erythrocytes may be adequate.3 W’ith that criterion, 100 per cent of the posterior placentas. 69 per cent of the anterior placentas. and two of three lateral placentas were successfully sampled by sonographicall) directed placental aspiration. This compares favorably with the one other report of placental aspiration of anterior placentas.3 The largest reported series of patients in whom fetal blood sampling was attempted under fetoscopic \isualization of the placenta claimed success in 19 of 20 instances with a posterior placenta and -1 of 6 instances with an anterior placenta. 2 However, no definition of success was given in this paper. If the two methods have essentially similar success rates, which is the better method for obtaining fetal erythrocytes will depend on which is safer. There is insufficient. experience with either method at this time to make ;~ny rstimates of safety: however, use of I he fetoscope in the presence of. an anteriolplacenta is of considerable coIlcern. Regardless of technique. we agree it-ith Hobbins and Mahonev’ that fetal blood sampling should be done after 18 weeks’ gestation, since with irlcreasing gcstation a given blood loss represents a smaller proportion of the fetal blood volume. Although we have employed this technique IO successfull\diagnose P-thalassemia and sickle cell anemia in utero;* 5 ’ the method’s shortcomings should be noted. The only case of amnionitis followed two successive days of attempting to obtain fetal blood. There probably was a break in the sterile technique on the second day, and the amniotic fluid containing maternal blood from the first day’s efforts provided an excellent culture medium. We now feel t.hat if initial attempts at fetal blood sampling are unsllcc-essful one should wait 7 to 10 days before a second set ofattempts. This will allow for reabsorption of blood in the amniotic fluid. W’e are concerned also with the question of fetal-maternal transfusion and isoimmunization and accordingly have begun an ongoing project of estimating the fetal-maternal transfusion induced b\ placental aspiration. We conclude that fetal erythrocytes for genetic studies can be obtained by sonographicallv directed
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Fetal
placental
aspiration.
potential
benefits
This of fetal
technique blood
is simple,
sampling
are
and
the
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REFERENCES
I.
Hobbins, J. C., and utero diagnosis of obtaining fetal blood, 2. Hobbins, J. C., and Lancet 2: 107, 1975. 3. Kan, Y. W., Valenti, Rieder. R. F.: Foetal 1974.
Mahoney, M. J.: Progress toward in hemoglobinopathies-technique for N. Engl. J. Med. 290: 1065, 1974. Mahoney, M. J.: Fetal blood drawing, C., Carnazza, blood sampling
V., Guidotti, R., and in utero, Lancet 1: 79,
to and
warrant
blood
further
sampling
in midtrimester
investigations
pregnancies
of
its
655
effectiveness
safety.
4. Kazazian, H. H., Kaback, M. M., Woodhead, A. P., Leonard, C. O., and Nersesian, W. S.: Further studies on the antenatal detection of sickle cell anemia and other hemoglobinopathies, Adv. Exp. Med. Biol. 28: 337, 1972. 5. Kan, Y. W., Golbus, M. S., Trecartin, R.. Furbetta, M., and Cao, A.: Prenatal diagnosis of homozygous P-thalassemia, Lancet 2: 790, 1975. 6. Kan, Y. W., Golbus, M. S., and Trecartin, R.: Prenatal diagnosis of sickle cell anemia. Submitted for publication.