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Second-trimester echogenic bowel and intraamniotic bleeding: Association between fetal bowel echogenicity and amniotic fluid spectrophotometry at 410 nm
Second-trimester echogenic bowel and intraamniotic bleeding: Association between fetal bowel echogenicity and amniotic fluid spectrophotometry at 410 nm Waldo Sepulveda, MD, Rosemary Reid, MD, Peter Nicolaidis, MD, Oonagh Prendiville, BSc, Richard S. Chapman, PhD, and Nicholas Mo Fisk, PhD London, United Kingdom, and Athens, Greece OBJECTIVE: Out purpose was to determine whether the presence of heme pigments in amniotic fluid is associated with the ultrasonographic findings of increased fetal bowel echogenicity in the second trimester. STUDY DESIGN: Spectrophotometric analysis of amniotic fluid for optical density at 410 nm was prospectively performed to study the presence of heme pigments in (1) 104 pregnancies undergoing second-trimester amniocentesis for routine cytogenetic indications and (2) in 14 pregnancies undergoing amniocentesis for prenatal karyotyping because of fetal strongly echogenic bowel. In the routine amniocentesis group the fetal small bowel echogenicity was assessed immediately before amniocentesis and classified as nonechogenic (n = 64), mildly echogenic (n = 36), or hyperechogenic (n = 4) with the fetal iliac wing and liver used as references. Only amniotic fluid specimens that were obtained at the first attempt and that were not blood-stained were ncluded in this study, with the first milliliter being discarded in all samples. RESULTS. In the routine amniocentesis group abnormal amniotic fluid optical density readings were significantly more frequent in fetuses with increased bowel echogenicity compared with those with nonechogenic bowel (8/40 [20%] vs 3/64 [5%], respectively; p < 0.001). In the hyperechogenic bowel group abnormal amniotic fluid optical density readings were found in four samples (29%). Overall, 12 of 54 fetuses (22%) with increased bowel echogenicity had a detectable peak at 410 nm. Three of the 12 (25%) fetuses with echogenic bowel and positive readings for hemoglobin were chromosomally abnormal. CONCLUSIONS: Fetal smal[ bowel echogenioity is associated with the presence of heme pigments in amniotic fluid as determinecl by amniotic fluid opticat density at 410 nm. Swallowing of amniotic fluid after intraamniotic bleeding seems impiicated in the etiology of second-trimester echogenic bowel in both euploid and aneuploid fetuses. (AM J OBSTETGYNECOL1996;174:839-42,)
Key words: Echogenic bowel, intraamniotic bleeding, amniotic fluid, optical density at 410 nm, ultrasonography
Increased echogenicity of the fetal small bowel is a common finding during second-trimester ultrasonographic examination; however, its exact etiopathologic mechanism remains unknown. In normal fetuses it has been suggested that this ulU-asonographic linding represents an arti~~tct resulting from reflection of the ultrasonography beam from the wall of collapsed loops of bowel.a, 2 In abnormal disorders it has been suggested to represent intraluminal inspissated meconium, decreased From the Centrefor Fetal Care, Royal Postgraduate Medical School, bzstitute of Obstetrics and Co,naecology, Queen Charlotte's and Chelsea Hospital, the Department of Chemical Pathology, Hamm«rsmith Hospital, and the Fetal Medicine Unit, Mitera Materni~y Hospital, Presented at the Fifteenth Annual Meeting of the Sodety of PerinataI Obstetricians, Atlanta, Georgia,January 2.3-28, 1995. Receivedfor publication May 17, 1995; revisedJuly '7, 1995; aceeflted August 9, 1995. Reprbzts not availablefrom the authors. Copyright © 1996 by Mosby-Year Book, Inc. 0002-9378/90 $5.00 + 0 6/1/68434
water content of meconium, hypercellular meconium, or mesenteric ischemia, assumptions based on the high frequency of echogenic bowel in cystic fibrosis, intrauterine growth retardation, and bowel obstruction. ~a We recendy reported an association between echogenic bowel and intraamniotic bleeding. 9 In the current smdy we examine prospectively the hypothesis that increased fetal bowel echogenicity is due to swatlowed bloody amniotic fluid after intraamniotic bleeding. We therefore evaluated fetal small bowel echogenicity at second-trimester amniocentesis in relation to the presence of heme pigments in amniotic fluid as determined by spectrophotometry at 410 nm.
Material and methods
Spectrophotometric analysis of amniotic fluid for optical density at 410 n m (OD41o) was prospecfively performed to determine the presence of heme pigments in 839
840
Sepulvedaet ai.
two study groups. The first consisted of 104 singleton pregnancies undergoing second-trimester amniocentesis for routine cytogenetic indications (i.e., advanced maternal age or positive maternal serum screening for Down syndrome) at a median gestational age of 16 weeks (fange 15 to 18 weeks). In all these cases an ultrasonographic examination was performed immediately before amniocentesis to determine fetal viability, fetal position, and placental location. The ultrasonographic pattern of the fetal small bowel was assessed immediately before amniocentesis and classified as follows: (1) nonechogenic, when the fetal bowel had similar echogenicity to the fetal liver, (2) mildly echogenic, when the fetal bowel was more echogenic than the fetal liver but less echogenic than the iliac wing, and (3) strongly echogenic, when the fetal bowel echogenicity was similar to the fetal iliac wing. The second group consisted of 14 pregnancies undergoing amniocentesis for prenatal karyotyping because of hyperechogenic fetal bowel at a median gestational age of 19 weeks (range 18 to 21 weeks). These cases were detected at detailed second-trimester ultrasonography and the diagnosis was confirmed before amniocentesis. None of the women had elevated second-trimester maternal serum c¢-fetoprotein levels, and one in each group had a history of significant early pregnancy bleeding. After each woman gave informed consent for the study, as approved by the institutional ethics committee, amniocentesis was performed in a standard fashion with a 20gauge needle u n d e r continuous ultrasonographic control. Fresh blood-stained samples and those obtained by transplacental passage or at the second or subsequent attempts were excluded from the study. Dark-brown specimens, tbought to represent previous intraamniotic bleeding,9 were, however, included. After the first milliliter was discarded, 15 to 20 ml was aspirated for karyotyping. Some of the samples in the hyperechogenic bowel group were also tested for cystic fibrosis. 1° An aliquot of 2 ml was collected in a sterile plastic container and placed in a dark plastic bag to protect the specimen from light. The sample was transported to the laboratory and centrifuged at 1000 g for 10 minutes to remove cellular material and debris. The supernatant was then transferred to a 1 ml light-path silica cuvette and scanned in a clinical spectrophotometer (Philips PU 8720, Cambridge, United Kingdom) at 320, 410, and 550 nm, with distilled water used as blank. To establish the baseline value, a line constructed between the readings at 320 and 500 n m was drawn on semilogarithmic paper. The A 0D410 was determined by measuring the deviation between the spectrophotometric reading at 410 n m and the intercept at 410 n m on the baseline. 11 Because it was not possible to determine readings when high concentrations of pigments were present, dark-brown amniotic fluid samples were diluted with distilled watet before measurements were made. The values were then plotted in a linear graph
March 1996 AmJ ObstetGynecol
paper for visual assessment; the presence of hemoglobin was deteeted by the identifieation of a peak at 410 n m (Fig. 1). Karyotyping was performed with standard eytogenefic techniques. Comparisons between groups and subgroups were performed uäth Fisher's exact test. A p value <0.05 was considered statistically significant.
Results In women undergoing amniocentesis for routine cytogenetie indications, the fetal small bowel was classified as nonechogenie in 64, mildly echogenic in 36, and strongly echogenic in 4. Abnormal 0D41 o readings were found in 3 fetuses with nonechogenie bowel, in 6 with mildly echogenic bowel (1 ofwhom had early pregnancy bleeding), and in 2 with strongly echogenic bowel; only 1 of the 4 fetuses with strongly echogenic bowel had dark-brown amniotic fluid. Abnormal OD41o readings were signifieantly more frequent in fetuses with increased bowel echogenicity compared with those with nonechogenic bowel (8/40 [20%] vs 3/64 [5%], respectively; p < 0.001). Similarly, fetuses with abnormal OO410 readings were more likely to have increased bowel echogenicity at amniocentesis than to have normal bowel appearance (8/11 [73%] vs 3/11 [27%], p < 0.001). In women undergoing amniocentesis because of hyperechogenic bowel, abnormal OD410 readings were found in 4 of the 14 samples (29%), 1 ofwhich was dark-brown. An abnormal karyotype was found in two fetuses in the routine amniocentesis group (2%) and in three of the fetuses undergoing amniocentesis because of hyper echogenie bowel (21%). In the routine amniocentesis group there were two fetuses with Down syndrome; both had normal bowel echogenicity, elear amniotic fluid at amnioeentesis, and normal OD410 readings. In the hyperechogenic bowel group there were two fetuses with trisomy 18 and one with trisomy 9; all three had abnormal OD41o readings and one trisomy 18 fetus had dark-brown fluid. Overall, fetuses with hyperechogenie bowel had a greater incidence of aneuploidy than did fetuses with either normal or mildly echogenic bowel (3/18 [17%] vs 2/100 [2%], respectively; p < 0.05). Furthermore, fetuses with abnormal 0D41 o readings had a greater incidence of aneuploidy than did those with normal readings (3/15 [20%] vs 2/103 [2%], respectively; p < 0.01). Three of the 12 (25%) fetuses with echogenic bowel and positive OD41o readings for hemoglobin were chromosomally abnormal.
Comment In this study we report a significant association between 0D41 o readings and small bowel eehogenicity in secondtrimester fetuses. Because OO41o readings indicate the presence or absenee of heme pigments, this association supports our previous observation that fetuses with
Sepulveda et al. 841
Volume 174, Number 3 AmJ Obstet Gynecol
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Fig. 1. A, Amniotic fluid OD410shou4ng no heme pigments in amniotic fluid. B, Sample ~4th moderate amount of pigments. C, Dark-brown amniotic fluid sampIe "after dilution (x3) demonstraüng large amount of pigments. ABS, Absorbency.
proved intraamniotic bleeding have a higher incidence of increased bowel echogenicity at second-trimester scan. 9 In our previous study a significant associadon between the color of amniodc fluid obtained at amniocentesis and subsequent fetal bowel echogenicity at detailed secondtrimester ultrasonography was noted; fetuses with darkbrown or fresh blood-stained amniotic fluid subsequently had a significantly greater incidence of echogenie bowel than did those fetuses with clear samples. 9 However, our previous smdy was retrospective and no correlation with the bowel eehogenicity at the time of amniocentesis was obtained, in part because of the unrecognized association of intraamniotic bleeding and hyperechogenic bowel at that time. In the eurrent study we evaluated prospectively this association with speetrophotometry at 410 nm as an objective measurement of the presence of heme pigments in amniotic fluid, n We reduced the chance of blood contamination from a traumatic procednre by selecting only those samples that were not freshly blood stained, that were obtained at the frst attempt by a nontransplacental approach, and in which the first aliquot was discarded. In this setting we found a significant association between increased fetal bowel echogenicity and the presence of hemoglobin in amniotic fluid. Because the fems normally swallows considerable volumes of amniotie fluid, we suggest that second-trimester echogenie bowel results, at least in a eonsiderable n u m b e r of cases, from the presence of blood in the fetal gastrointestinal tract from swallowed blood after intraamniotic bleeding. Increased fetal bowel echogenicity therefore could be the ultrasonographic manifestation of blood clots or hypercellular meconium from blood cells in the fetal small bowel. However, why only some, but not all, fetuses with evidence of intraamniotic bleeding had echogenic bowel remains to be determined, hut the duration of the intraamniotic bleeding episode or the gestational age at bleeding may play a role in its etiopathogenesis.
One of the most important clinicatly significant factors of echogenic bowel is its association with fetal aneuploidy. Since the initial article repordng such an association, ~~several other series have confirmed these findings.6' ~s. 14 Indeed, our incidence of aneuploidy of 21% in 14 fetuses undergoing prenatal karyotyping because of hyperechogenic bowel is between the 27% rate repoyted by Scioscia et alF'3 and the 16% rate recently reported by Bromley et al. t4 It is noteworthy that our current study found evidence ofintraamniotic bleeding in both euploid and aneuploid fetuses with echogenic bowel. Therefore care should be taken before attributing echogenic bowel simply to intraamniotic bleeding; detection ofother ultrasonographic feamres suggestive ofintraamniotic blecding such as intraamniotic blood clots, chorioamniotic separation, and intraluminal gastric masses ~547should therefore not curtail prenatal assessment and prenatat karyotyping should be still offered. Because intraamniotic bleeding carries an increased risk of aneuploidy, probably as a resutt of abnormal placentation,is we postulate that the lncreased incidence of aneuploidy in the fetus väth e chogenic bowel could be the indirect resutt of early pregnancy intraamniotic bleeding. Indeed0 three of the five aneuploid fetuses in our series had evidence ofintraamniotic bleeding; one had dark-brown fluid, and the remaining two had clear amniotic fluid at amniocentesis but abnormal OD410 readings. Both femses with Down syndrome in our series had normal bowel echogeniciry; therefore it was not possible to prove the hypothesis that hyperechogenic bowel in trisomy 21 fetuses is due to 111traamniotie bleeding. Similarly, eehogenic bowel is associated with intrauterine growth retardation and intrauterine fetal death. 5 6. 1«Because pregnancles in which darkbrown amniotic fluid is obtained at amniocentesis are also at increased risk of these complications,ag2awe suggest that the associatiQn ofeehogenic bowel and poor perinatal outcome in euploid fetuses may also be explained by preexisting intraamniotic bleeding.
842 Sepulvedaet al.
In c o n c l u s i o n , o u r data suggest t h a t swallowed a m n i otic fluid after i n t r a a m n i o t i c b l e e d i n g is a m a j o r p a t h o physiologic m e c h a n i s m for i n c r e a s e d fetal bowel e c h o g e nicity. A m n i o t i c fluid s p e c t r o p h o t o m e t r y at 410 n m is useful to d o c u m e n t i n t r a a m n i o t i c b l e e d i n g in fetuses with e c h o g e n i c bowel u n d e r g o i n g cytogenetic a m n i o c e n tesis. This c o u l d e x p l a i n i n c r e a s e d bowel e c h o g e n i c i t y a n d s h o u l d a l e r t t h e physician to t h e i n c r e a s e d risk of p o o r p e r i n a t a l o u t c o m e in e u p l o i d fetuses. REFERENCES
1. FakhryJ, Reiser M, Shapiro LR, Schecter A, Pait LP, Glennon A. Increased echogenicity in the lower fetal abdomen: a common normal variant in the second trimester. J Ultrasound Med 1986;5:489-92. 2. Parulekar SG. Sonography of normal fetal bowel. J Ultrasound Med 1991;10:211-20. 3. Muller F, Aubry MC, Gasser B, Duchatel E Boue J, Boue A. Prenatal diagnosis of cystic fibrosis, II: meconium ileus in affected fetuses. Prenat Diagn 1985;5:109-17. 4. Caspi B, Elchalal U, Lancet M, ChemkeJ. Prenatal diagnosis of cystic fibrosis: ultrasonographic appearance of meconium ileus in the fetus. Prenat Diagn 1988;8:379-82. 5. Dicke JM, Crane JE Sonographically detected hyperechoic fetal bowel: significance and implication for pregnancy management. Obstet Gynecol 1992;80:778-82. 6. Nyberg DA, Dubinsky T, Resta RG, Mahony BS, Hickok DE, Luthy DA. Echogenic fetal boweI during the second trimester: clinical importance. Radiology 1993;188:527-31. 7. Ewer AK, McHugo JM, Chapman S, Newell SJ. Fetal echogenic gq't: a marker ofintrauterine gut ischaemia? Arch Dis Child 1993;69:510-3. 8. Gollin Y, Gollin G, Shafer W, CopelJ. Increased abdominal echogenicity in utero: a marker for intestinal obstruction? [Abstract] AMJ OBSTE:rGYN~COL1993;168:349. 9. Sepulveda W, Hollingsworth J, Bower S, Vaughan JI, Fisk NM. Fetal hyperechogenic bowel after intra-amniotic bleeding. Obstet Gynecol 1994;83:947-50.
March 1996 Am J Obstet Gynecol
10. Sepulveda W, Leung KY,'Robertson ME, Kay E, Mayall ES, Fisk NM. Prevalence of cystic fibrosis mutations in pregnancies with fetal echogenic bowel. Obstet Gynecol I996;87: 103-6. 11. Tietz NW. Textbook of clinical chemistry. Philadelphia: WB Saunders, 1985. 12. Nyberg DA, Resta RG, Luthy DA, Hickok DE, Mahony BS, Hirsch JH. Prenatal sonographic findings of Down syndrome: review of 94 cases. Obstet Gynecol 1990;76:370-7. 13. Scioscia AL, Pretorius DH, Budorick NE, Cahill TC, Axelrod FT, Leopold GR. Second-trimester echogenic bowel and chromosomal abnormalities. A.\«J OBSTETGYNECOL1992;167: 889-94. 14. Bromley B, Doubilet E Frigoletto FD, I@auss C, EstroffJA, BenacerrafBR. Is fetal hyperechoic bowet on second trimester sonogram an indication for amniocentesis? Obstet Gynecol 1994;83:647-51. 15. Borlum KG. Second trimester chorioamniotic separation and amniocentesis. EurJ Obstet Gynecol Reprod Biol 1989; 30:35-8. 16. Chinn DH, Towers CV, Beeman RG, Miller EI. Sonographically demonstrated intraamniotic hemorrhage following transplacental genetic amniocentesis. Frequency, sonographic appearance, and clinical significance. J Ultrasound Med 1990;9:495-501. 17. Daly-Jones E, Sepulveda W, HollingsworthJ, Fisk NM. Fetal intraluminal gastric masses after second trimester amniocentesis. J Ultrasound Med 1994;13:963-6. 18. Isada NB, Koppitch FC, Johnson MP, Evans MI. Does the color of amniotic fluid still marter? Fetal Diagn Ther 1990; 5:165-7. 19. Hankins GDV, Rowe J, QuirkJG, Trubey R, Strickland DM. Significance of brown a n d / o r green amniotic fluid at the time of second trimester geneüc amniocentesis. Obstet Gynecol 1984;64:353-8. 20. Hess LW, Anderson RL, Golbus MS. Significance of opaque discolored amniotic fluid at second-trimester amniocentesis. Obstet Gynecol 1986;67:44-6. 21. Zorn EM, Hanson FW, Greve LC, Phelps-Sandall B, Tennant FR. kalalysis of the significance of discolored amniotic fluid detected at midtrimester amniocentesis. AM J OBSTET GYNECOL1986;154:123440.
Key words: Echogenic bowel, intraamniotic bleeding, amniotic fluid, optical density at 410 nm, ultrasonography
Increased echogenicity of the fetal small bowel is a common finding during second-trimester ultrasonographic examination; however, its exact etiopathologic mechanism remains unknown. In normal fetuses it has been suggested that this ulU-asonographic linding represents an arti~~tct resulting from reflection of the ultrasonography beam from the wall of collapsed loops of bowel.a, 2 In abnormal disorders it has been suggested to represent intraluminal inspissated meconium, decreased From the Centrefor Fetal Care, Royal Postgraduate Medical School, bzstitute of Obstetrics and Co,naecology, Queen Charlotte's and Chelsea Hospital, the Department of Chemical Pathology, Hamm«rsmith Hospital, and the Fetal Medicine Unit, Mitera Materni~y Hospital, Presented at the Fifteenth Annual Meeting of the Sodety of PerinataI Obstetricians, Atlanta, Georgia,January 2.3-28, 1995. Receivedfor publication May 17, 1995; revisedJuly '7, 1995; aceeflted August 9, 1995. Reprbzts not availablefrom the authors. Copyright © 1996 by Mosby-Year Book, Inc. 0002-9378/90 $5.00 + 0 6/1/68434
water content of meconium, hypercellular meconium, or mesenteric ischemia, assumptions based on the high frequency of echogenic bowel in cystic fibrosis, intrauterine growth retardation, and bowel obstruction. ~a We recendy reported an association between echogenic bowel and intraamniotic bleeding. 9 In the current smdy we examine prospectively the hypothesis that increased fetal bowel echogenicity is due to swatlowed bloody amniotic fluid after intraamniotic bleeding. We therefore evaluated fetal small bowel echogenicity at second-trimester amniocentesis in relation to the presence of heme pigments in amniotic fluid as determined by spectrophotometry at 410 nm.
Material and methods
Spectrophotometric analysis of amniotic fluid for optical density at 410 n m (OD41o) was prospecfively performed to determine the presence of heme pigments in 839
840
Sepulvedaet ai.
two study groups. The first consisted of 104 singleton pregnancies undergoing second-trimester amniocentesis for routine cytogenetic indications (i.e., advanced maternal age or positive maternal serum screening for Down syndrome) at a median gestational age of 16 weeks (fange 15 to 18 weeks). In all these cases an ultrasonographic examination was performed immediately before amniocentesis to determine fetal viability, fetal position, and placental location. The ultrasonographic pattern of the fetal small bowel was assessed immediately before amniocentesis and classified as follows: (1) nonechogenic, when the fetal bowel had similar echogenicity to the fetal liver, (2) mildly echogenic, when the fetal bowel was more echogenic than the fetal liver but less echogenic than the iliac wing, and (3) strongly echogenic, when the fetal bowel echogenicity was similar to the fetal iliac wing. The second group consisted of 14 pregnancies undergoing amniocentesis for prenatal karyotyping because of hyperechogenic fetal bowel at a median gestational age of 19 weeks (range 18 to 21 weeks). These cases were detected at detailed second-trimester ultrasonography and the diagnosis was confirmed before amniocentesis. None of the women had elevated second-trimester maternal serum c¢-fetoprotein levels, and one in each group had a history of significant early pregnancy bleeding. After each woman gave informed consent for the study, as approved by the institutional ethics committee, amniocentesis was performed in a standard fashion with a 20gauge needle u n d e r continuous ultrasonographic control. Fresh blood-stained samples and those obtained by transplacental passage or at the second or subsequent attempts were excluded from the study. Dark-brown specimens, tbought to represent previous intraamniotic bleeding,9 were, however, included. After the first milliliter was discarded, 15 to 20 ml was aspirated for karyotyping. Some of the samples in the hyperechogenic bowel group were also tested for cystic fibrosis. 1° An aliquot of 2 ml was collected in a sterile plastic container and placed in a dark plastic bag to protect the specimen from light. The sample was transported to the laboratory and centrifuged at 1000 g for 10 minutes to remove cellular material and debris. The supernatant was then transferred to a 1 ml light-path silica cuvette and scanned in a clinical spectrophotometer (Philips PU 8720, Cambridge, United Kingdom) at 320, 410, and 550 nm, with distilled water used as blank. To establish the baseline value, a line constructed between the readings at 320 and 500 n m was drawn on semilogarithmic paper. The A 0D410 was determined by measuring the deviation between the spectrophotometric reading at 410 n m and the intercept at 410 n m on the baseline. 11 Because it was not possible to determine readings when high concentrations of pigments were present, dark-brown amniotic fluid samples were diluted with distilled watet before measurements were made. The values were then plotted in a linear graph
March 1996 AmJ ObstetGynecol
paper for visual assessment; the presence of hemoglobin was deteeted by the identifieation of a peak at 410 n m (Fig. 1). Karyotyping was performed with standard eytogenefic techniques. Comparisons between groups and subgroups were performed uäth Fisher's exact test. A p value <0.05 was considered statistically significant.
Results In women undergoing amniocentesis for routine cytogenetie indications, the fetal small bowel was classified as nonechogenie in 64, mildly echogenic in 36, and strongly echogenic in 4. Abnormal 0D41 o readings were found in 3 fetuses with nonechogenie bowel, in 6 with mildly echogenic bowel (1 ofwhom had early pregnancy bleeding), and in 2 with strongly echogenic bowel; only 1 of the 4 fetuses with strongly echogenic bowel had dark-brown amniotic fluid. Abnormal OD41o readings were signifieantly more frequent in fetuses with increased bowel echogenicity compared with those with nonechogenic bowel (8/40 [20%] vs 3/64 [5%], respectively; p < 0.001). Similarly, fetuses with abnormal OO410 readings were more likely to have increased bowel echogenicity at amniocentesis than to have normal bowel appearance (8/11 [73%] vs 3/11 [27%], p < 0.001). In women undergoing amniocentesis because of hyperechogenic bowel, abnormal OD410 readings were found in 4 of the 14 samples (29%), 1 ofwhich was dark-brown. An abnormal karyotype was found in two fetuses in the routine amniocentesis group (2%) and in three of the fetuses undergoing amniocentesis because of hyper echogenie bowel (21%). In the routine amniocentesis group there were two fetuses with Down syndrome; both had normal bowel echogenicity, elear amniotic fluid at amnioeentesis, and normal OD410 readings. In the hyperechogenic bowel group there were two fetuses with trisomy 18 and one with trisomy 9; all three had abnormal OD41o readings and one trisomy 18 fetus had dark-brown fluid. Overall, fetuses with hyperechogenie bowel had a greater incidence of aneuploidy than did fetuses with either normal or mildly echogenic bowel (3/18 [17%] vs 2/100 [2%], respectively; p < 0.05). Furthermore, fetuses with abnormal 0D41 o readings had a greater incidence of aneuploidy than did those with normal readings (3/15 [20%] vs 2/103 [2%], respectively; p < 0.01). Three of the 12 (25%) fetuses with echogenic bowel and positive OD41o readings for hemoglobin were chromosomally abnormal.
Comment In this study we report a significant association between 0D41 o readings and small bowel eehogenicity in secondtrimester fetuses. Because OO41o readings indicate the presence or absenee of heme pigments, this association supports our previous observation that fetuses with
Sepulveda et al. 841
Volume 174, Number 3 AmJ Obstet Gynecol
ABS
2,0
2,0~
2.0-
B
A
1.5~
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350 400 450 500 550 600
0.04 300
350
400 450 500 550 600
OPTICAL DENSITY (nm)
Fig. 1. A, Amniotic fluid OD410shou4ng no heme pigments in amniotic fluid. B, Sample ~4th moderate amount of pigments. C, Dark-brown amniotic fluid sampIe "after dilution (x3) demonstraüng large amount of pigments. ABS, Absorbency.
proved intraamniotic bleeding have a higher incidence of increased bowel echogenicity at second-trimester scan. 9 In our previous study a significant associadon between the color of amniodc fluid obtained at amniocentesis and subsequent fetal bowel echogenicity at detailed secondtrimester ultrasonography was noted; fetuses with darkbrown or fresh blood-stained amniotic fluid subsequently had a significantly greater incidence of echogenie bowel than did those fetuses with clear samples. 9 However, our previous smdy was retrospective and no correlation with the bowel eehogenicity at the time of amniocentesis was obtained, in part because of the unrecognized association of intraamniotic bleeding and hyperechogenic bowel at that time. In the eurrent study we evaluated prospectively this association with speetrophotometry at 410 nm as an objective measurement of the presence of heme pigments in amniotic fluid, n We reduced the chance of blood contamination from a traumatic procednre by selecting only those samples that were not freshly blood stained, that were obtained at the frst attempt by a nontransplacental approach, and in which the first aliquot was discarded. In this setting we found a significant association between increased fetal bowel echogenicity and the presence of hemoglobin in amniotic fluid. Because the fems normally swallows considerable volumes of amniotie fluid, we suggest that second-trimester echogenie bowel results, at least in a eonsiderable n u m b e r of cases, from the presence of blood in the fetal gastrointestinal tract from swallowed blood after intraamniotic bleeding. Increased fetal bowel echogenicity therefore could be the ultrasonographic manifestation of blood clots or hypercellular meconium from blood cells in the fetal small bowel. However, why only some, but not all, fetuses with evidence of intraamniotic bleeding had echogenic bowel remains to be determined, hut the duration of the intraamniotic bleeding episode or the gestational age at bleeding may play a role in its etiopathogenesis.
One of the most important clinicatly significant factors of echogenic bowel is its association with fetal aneuploidy. Since the initial article repordng such an association, ~~several other series have confirmed these findings.6' ~s. 14 Indeed, our incidence of aneuploidy of 21% in 14 fetuses undergoing prenatal karyotyping because of hyperechogenic bowel is between the 27% rate repoyted by Scioscia et alF'3 and the 16% rate recently reported by Bromley et al. t4 It is noteworthy that our current study found evidence ofintraamniotic bleeding in both euploid and aneuploid fetuses with echogenic bowel. Therefore care should be taken before attributing echogenic bowel simply to intraamniotic bleeding; detection ofother ultrasonographic feamres suggestive ofintraamniotic blecding such as intraamniotic blood clots, chorioamniotic separation, and intraluminal gastric masses ~547should therefore not curtail prenatal assessment and prenatat karyotyping should be still offered. Because intraamniotic bleeding carries an increased risk of aneuploidy, probably as a resutt of abnormal placentation,is we postulate that the lncreased incidence of aneuploidy in the fetus väth e chogenic bowel could be the indirect resutt of early pregnancy intraamniotic bleeding. Indeed0 three of the five aneuploid fetuses in our series had evidence ofintraamniotic bleeding; one had dark-brown fluid, and the remaining two had clear amniotic fluid at amniocentesis but abnormal OD410 readings. Both femses with Down syndrome in our series had normal bowel echogeniciry; therefore it was not possible to prove the hypothesis that hyperechogenic bowel in trisomy 21 fetuses is due to 111traamniotie bleeding. Similarly, eehogenic bowel is associated with intrauterine growth retardation and intrauterine fetal death. 5 6. 1«Because pregnancles in which darkbrown amniotic fluid is obtained at amniocentesis are also at increased risk of these complications,ag2awe suggest that the associatiQn ofeehogenic bowel and poor perinatal outcome in euploid fetuses may also be explained by preexisting intraamniotic bleeding.
842 Sepulvedaet al.
In c o n c l u s i o n , o u r data suggest t h a t swallowed a m n i otic fluid after i n t r a a m n i o t i c b l e e d i n g is a m a j o r p a t h o physiologic m e c h a n i s m for i n c r e a s e d fetal bowel e c h o g e nicity. A m n i o t i c fluid s p e c t r o p h o t o m e t r y at 410 n m is useful to d o c u m e n t i n t r a a m n i o t i c b l e e d i n g in fetuses with e c h o g e n i c bowel u n d e r g o i n g cytogenetic a m n i o c e n tesis. This c o u l d e x p l a i n i n c r e a s e d bowel e c h o g e n i c i t y a n d s h o u l d a l e r t t h e physician to t h e i n c r e a s e d risk of p o o r p e r i n a t a l o u t c o m e in e u p l o i d fetuses. REFERENCES
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