RESUMO
OBJECTIVE: The aim of this study was to evaluate the maternal and ultrasonographic characteristics of pregnant women who underwent cervical length (CL) measurement by transvaginal ultrasound between 11 and 13 + 6 weeks of gestation and who delivered at term or preterm. METHODS: A retrospective cohort study was carried out between March 2013 and December 2018 by analyzing ultrasound data of singleton pregnant women who underwent CL measurement by transvaginal ultrasound during the first trimester scan. CL was compared between the two groups (full-term and preterm birth [PB]) using Student's t-test. RESULTS: A total of 5097 pregnant women were enrolled, of whom 5061 (99.3%) had term and 36 (0.7%) had PB < 34 weeks. CL measurements did not differ between the term and preterm groups (36.62 vs. 37.83 mm, p = 0.08). Maternal age showed a significant and linear association with CL (r = 0.034, p = 0.012) and CRL (r = 0.086, p < 0.001). Smoking status was associated with shorter CL (36.64 vs. 35.09 mm, p = 0.003). When we analyzed the CL of the pregnant women in the term and preterm groups, according to the gestational age cut-offs for prematurity (28, 30, 32, and 34 weeks), we found that there was no significant difference between the measurements in all groups (p > 0.05). CONCLUSION: We observed no significant differences between CL measurements between 11 and 13 + 6 weeks in pregnant women who had preterm and term deliveries. Gestational age and CRL showed a significant and linear association with CL measurement.
Assuntos
Medida do Comprimento Cervical , Colo do Útero , Nascimento Prematuro , Humanos , Feminino , Gravidez , Medida do Comprimento Cervical/métodos , Estudos Retrospectivos , Adulto , Nascimento Prematuro/diagnóstico por imagem , Colo do Útero/diagnóstico por imagem , Estudos de Coortes , Nascimento a Termo , Primeiro Trimestre da Gravidez , Idade Gestacional , Ultrassonografia Pré-Natal/métodosRESUMO
OBJECTIVE: To evaluate the association between Doppler patterns in fetuses with Down syndrome (DS) and their placental histopathologic findings. METHODS: A retrospective cross-sectional study was performed by collecting data from medical records of singleton pregnancies between January 2014 and January 2022, whose fetuses had a confirmed diagnosis of DS either prenatally or postnatally. Placental histopathology, maternal characteristics, and prenatal ultrasound (biometric parameters and umbilical artery [UA] Doppler) were evaluated. RESULTS: Of 69 eligible pregnant women, 61 met the inclusion and exclusion criteria. In the sample, 15 fetuses had an estimated fetal weight < 10th percentile for gestational age (GA) and were considered small for gestational age (SGA). Thirty-eight fetuses had increased resistance on the UA Doppler. Histologic changes were detected in 100% of the placentas, the most common being delayed villous maturation, alterations associated with poor fetal vascular perfusion, and villous dysmorphism. More than 50% of the placentas showed alterations related to placental insufficiency. We did not observe a statistically significant association between UA Doppler examination and placental alterations. All placentas analyzed in the SGA subgroup showed findings compatible with placental insufficiency. CONCLUSION: We found no statistically significant association between placental histopathologic findings and UA Doppler abnormalities in fetuses with DS. The placental alterations identified were delayed villous maturation, alterations associated with poor fetal vascular perfusion, and villous dysmorphism.
Assuntos
Síndrome de Down , Placenta , Ultrassonografia Pré-Natal , Humanos , Feminino , Síndrome de Down/diagnóstico por imagem , Síndrome de Down/complicações , Síndrome de Down/fisiopatologia , Gravidez , Estudos Transversais , Estudos Retrospectivos , Ultrassonografia Pré-Natal/métodos , Adulto , Placenta/diagnóstico por imagem , Placenta/patologia , Placenta/irrigação sanguínea , Hemodinâmica/fisiologia , Ultrassonografia Doppler/métodos , Artérias Umbilicais/diagnóstico por imagem , Artérias Umbilicais/fisiopatologia , Feto/diagnóstico por imagemRESUMO
Selective intrauterine growth restriction (sIUGR) in monochorionic twin pregnancies is associated with greater morbidity and mortality for both fetuses when compared to singleton and dichorionic pregnancies. This retrospective cohort study aimed to assess the perinatal outcomes of monochorionic twin pregnancies affected by this disorder and conducted expectantly, by analyzing the results according to the end-diastolic flow in the umbilical artery Doppler of the smaller twin (type I: persistently forward/type II: persistently absent or reversed/type III: intermittently absent or reversed). Seventy-five monochorionic diamniotic twin pregnancies with sIUGR were included in this study. sIUGR was defined by estimated fetal weight below the 3rd centile for gestational age, or below the 10th centile, when associated with at least one of the following three criteria: abdominal circumference below the 10th percentile, umbilical artery pulsatility index of the smaller twin above the 95th percentile, or estimated fetal weight discordance of 25% or more. Perinatal outcomes were analyzed from the prenatal period to hospital discharge and included perinatal death, neurological injury, retinopathy of prematurity (ROP), bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), and sepsis. The mortality rate was 1.33% in this cohort. The overall morbidity rate was lower in type I twin pregnancies. In conclusion, this study shows that sIUGR type I has lower morbidity than types II and III in expectant management.
Assuntos
Países em Desenvolvimento , Retardo do Crescimento Fetal , Estudos de Coortes , Feminino , Retardo do Crescimento Fetal/diagnóstico por imagem , Retardo do Crescimento Fetal/epidemiologia , Humanos , Recém-Nascido , Gravidez , Resultado da Gravidez , Gravidez de Gêmeos , Estudos Retrospectivos , Gêmeos Monozigóticos , Ultrassonografia Pré-Natal , Artérias Umbilicais/diagnóstico por imagemRESUMO
OBJECTIVE: To identify antenatal predictors of adverse perinatal outcomes in a population of preterm fetuses with early placental insufficiency diagnosed by Doppler abnormalities. METHOD: In this cross-sectional study of a cohort of singleton pregnant women diagnosed with early placental insufficiency, relationships between perinatal variables (arterial and venous Doppler, gestational age, birth weight, oligohydramnios, estimated fetal weight, and fetal weight z-scores) and major neonatal complications were analyzed by logistic regression. RESULTS: Two hundred sixty-five women were delivered, between 24 and 33 weeks gestation. The overall frequency of intact survival was 57.9% (n = 154). Gestational age thresholds for best prediction of survival was 27 + 6 weeks and for intact survival was 29 + 0 weeks gestation. Fetal weight and absent/reversed ductus venosus a-wave were the main predictors of survival in the regression model. When fetal weight was substituted for fetal weight z-score, ductus venosus abnormal Doppler predicted mortality and absent or reversed umbilical artery diastolic velocities predicted intact survival. CONCLUSIONS: This study illustrates the impact of gestational age and fetal weight on perinatal outcomes in early placental insufficiency, with well-defined thresholds. Gestational age and fetal weight, or a combination of fetal weight z-scores and fetal Doppler parameters, were the best predictors of intact survival in our sample.
Assuntos
Retardo do Crescimento Fetal/diagnóstico por imagem , Peso Fetal , Idade Gestacional , Recém-Nascido Prematuro/fisiologia , Resultado da Gravidez , Ultrassonografia Pré-Natal , Adulto , Peso ao Nascer , Brasil , Estudos de Coortes , Estudos Transversais , Feminino , Retardo do Crescimento Fetal/mortalidade , Retardo do Crescimento Fetal/fisiopatologia , Peso Fetal/fisiologia , Humanos , Recém-Nascido , Insuficiência Placentária/diagnóstico por imagem , Insuficiência Placentária/fisiopatologia , Gravidez , Nascimento Prematuro/mortalidade , Nascimento Prematuro/fisiopatologia , Ultrassonografia Doppler , Artérias Umbilicais/diagnóstico por imagemRESUMO
PURPOSE: We aimed to evaluate the ADNEX MR scoring system for the prediction of adnexal mass malignancy, using a simplified magnetic resonance imaging (MRI) protocol. METHODS: In this prospective study, 200 patients with 237 adnexal masses underwent MRI between February 2014 and February 2016 and were followed until February 2017. Two radiologists calculated ADNEX MR scores using an MRI protocol with a simplified dynamic study, not a high temporal resolution study, as originally proposed. Sensitivity, specificity, positive and negative predictive values, likelihood ratios, and the area under the receiver operating characteristic curve were calculated (cutoff for malignancy, score ≥ 4). The reference standard was histopathologic diagnosis or imaging findings during >12 months of follow-up. RESULTS: Of 237 lesions, 79 (33.3%) were malignant. The ADNEX MR scoring system, using a simplified MRI protocol, showed 94.9% (95% confidence interval [CI], 87.5%-98.6%) sensitivity and 97.5% (95% CI, 93.6%-99.3%) specificity in malignancy prediction; it was thus highly accurate, like the original system. The level of interobserver agreement on simplified scoring was high (κ = 0.91). CONCLUSION: In a tertiary cancer center, the ADNEX MR scoring system, even based on a simplified MRI protocol, performed well in the prediction of malignant adnexal masses. This scoring system may enable the standardization of MRI reporting on adnexal masses, thereby improving communication between radiologists and gynecologists.
Assuntos
Anexos Uterinos/diagnóstico por imagem , Doenças dos Anexos/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Neoplasias Ovarianas/diagnóstico por imagem , Anexos Uterinos/anatomia & histologia , Anexos Uterinos/patologia , Doenças dos Anexos/patologia , Doenças dos Anexos/cirurgia , Adulto , Idoso , Feminino , Seguimentos , Humanos , Pessoa de Meia-Idade , Procedimentos Cirúrgicos Minimamente Invasivos/normas , Variações Dependentes do Observador , Neoplasias Ovarianas/patologia , Neoplasias Ovarianas/cirurgia , Valor Preditivo dos Testes , Estudos Prospectivos , Centros de Atenção TerciáriaRESUMO
A dramatic increase in twin pregnancies has been observed in the past few decades, primarily related to assisted reproductive techniques (ART) and increased average maternal age during pregnancy. Multiple pregnancies, compared to singleton pregnancies, are associated with greater perinatal morbidity and mortality. The present study evaluated the perinatal outcomes of pregnancies with discordant anomalous twins in a tertiary maternity ward in a developing country. Data were retrospectively collected from the Instituto Fernandes Figueira/FIOCRUZ, Brazil between January 2002 and December 2014. We identified 74 twin pregnancies with discordant anomalous twins. Final data analysis was based on 40 pregnancies. Congenital defects were classified according to the International Classification of Diseases: ICD-10: the digestive system was responsible in 27 (34%) cases; the central nervous system was responsible in 18 (22%) cases; the urinary tract was responsible in 14 (17%) cases; and the circulatory system was responsible in 14 (17%) cases. A total of 19 deaths occurred during the study period, and delivery before 30.4 weeks was a significant prediction of fetal death (p = .01). The presence of hydrops in the affected fetus was related to a higher number of deaths in healthy fetuses and contributed to a worse prognosis. The presence of this condition was the cause of 12 (55.6%) deaths in healthy fetuses. A 10 times higher risk of death of a normal co-twin was observed in cases of death of the anomalous twin (p = .002, OR 10.55, 95% CI: 1.9-58.52).
Assuntos
Anormalidades Congênitas/etiologia , Gravidez de Gêmeos , Adolescente , Adulto , Brasil , Países em Desenvolvimento , Doenças em Gêmeos/epidemiologia , Doenças em Gêmeos/etiologia , Feminino , Morte Fetal , Humanos , Lactente , Morte do Lactente , Recém-Nascido , Idade Materna , Gravidez , Resultado da Gravidez , Estudos Retrospectivos , Adulto JovemRESUMO
BACKGROUND: Zika virus (ZIKV) has been linked to central nervous system malformations in fetuses. To characterize the spectrum of ZIKV disease in pregnant women and infants, we followed patients in Rio de Janeiro to describe clinical manifestations in mothers and repercussions of acute ZIKV infection in infants. METHODS: We enrolled pregnant women in whom a rash had developed within the previous 5 days and tested blood and urine specimens for ZIKV by reverse-transcriptase-polymerase-chain-reaction assays. We followed women prospectively to obtain data on pregnancy and infant outcomes. RESULTS: A total of 345 women were enrolled from September 2015 through May 2016; of these, 182 women (53%) tested positive for ZIKV in blood, urine, or both. The timing of acute ZIKV infection ranged from 6 to 39 weeks of gestation. Predominant maternal clinical features included a pruritic descending macular or maculopapular rash, arthralgias, conjunctival injection, and headache; 27% had fever (short-term and low-grade). By July 2016, a total of 134 ZIKV-affected pregnancies and 73 ZIKV-unaffected pregnancies had reached completion, with outcomes known for 125 ZIKV-affected and 61 ZIKV-unaffected pregnancies. Infection with chikungunya virus was identified in 42% of women without ZIKV infection versus 3% of women with ZIKV infection (P<0.001). Rates of fetal death were 7% in both groups; overall adverse outcomes were 46% among offspring of ZIKV-positive women versus 11.5% among offspring of ZIKV-negative women (P<0.001). Among 117 live infants born to 116 ZIKV-positive women, 42% were found to have grossly abnormal clinical or brain imaging findings or both, including 4 infants with microcephaly. Adverse outcomes were noted regardless of the trimester during which the women were infected with ZIKV (55% of pregnancies had adverse outcomes after maternal infection in the first trimester, 52% after infection in the second trimester, and 29% after infection in the third trimester). CONCLUSIONS: Despite mild clinical symptoms in the mother, ZIKV infection during pregnancy is deleterious to the fetus and is associated with fetal death, fetal growth restriction, and a spectrum of central nervous system abnormalities. (Funded by Ministério da Saúde do Brasil and others.).
Assuntos
Sistema Nervoso Central/anormalidades , Morte Fetal , Retardo do Crescimento Fetal/virologia , Microcefalia/virologia , Complicações Infecciosas na Gravidez , Infecção por Zika virus/complicações , Zika virus/isolamento & purificação , Adolescente , Adulto , Encéfalo/anormalidades , Brasil/epidemiologia , Sistema Nervoso Central/embriologia , Feminino , Morte Fetal/etiologia , Retardo do Crescimento Fetal/epidemiologia , Feto/anormalidades , Idade Gestacional , Humanos , Pessoa de Meia-Idade , Gravidez , Nascimento Prematuro/epidemiologia , Ultrassonografia Pré-Natal , Adulto JovemRESUMO
Communicating an unfavorable diagnosis during prenatal care is a growing challenge in clinical practice, as more and more tests are being performed to screen for the main conditions affecting the pregnant woman and her fetus. The way patients receive and subsequently deal with bad news is directly influenced by how the news is communicated by the attending physician. Unfortunately, physicians receive little or no training in communicating bad news, and they generally feel quite uncomfortable about doing so. Although many physicians consider the saying that "there's no good way to break bad news" to be the truth, the maxim does not reflect the true picture. The scope of this article is to discuss, in light of the scientific literature and the experience of fetal medicine services, some recommendations that can help to deal with these difficult moments and improve patient care for the remainder of the pregnancy.
Assuntos
Cuidado Pré-Natal , Revelação da Verdade , Atitude do Pessoal de Saúde , Feminino , Humanos , Relações Médico-Paciente , Gravidez , Diagnóstico Pré-NatalRESUMO
Communicating an unfavorable diagnosis during prenatal care is a growing challenge in clinical practice, as more and more tests are being performed to screen for the main conditions affecting the pregnant woman and her fetus. The way patients receive and subsequently deal with bad news is directly influenced by how the news is communicated by the attending physician. Unfortunately, physicians receive little or no training in communicating bad news, and they generally feel quite uncomfortable about doing so. Although many physicians consider the saying that "there's no good way to break bad news" to be the truth, the maxim does not reflect the true picture. The scope of this article is to discuss, in light of the scientific literature and the experience of fetal medicine services, some recommendations that can help to deal with these difficult moments and improve patient care for the remainder of the pregnancy.
A comunicação de diagnósticos durante o pré-natal é um desafio crescente na prática clínica à medida que se realizam cada vez mais exames para o rastreio das principais patologias que acometem as gestantes e seus fetos. A recepção de uma má notícia e sua posterior elaboração pela paciente serão diretamente influenciadas pelo modo como ela foi comunicada pelo profissional assistente. Infelizmente, os médicos recebem pouco ou nenhum treinamento para transmitir más notícias e, em geral, sentem-se extremamente desconfortáveis com isso. Embora a máxima "não existe uma maneira boa de dar uma notícia ruim" seja admitida como verdade por muitos médicos, ela não é representativa da realidade. O objetivo deste artigo é discutir à luz da literatura científica e da prática em centros de medicina fetal algumas recomendações que podem facilitar a vivência desses momentos difíceis e melhorar o cuidado com os pacientes para o prosseguimento da gestação.
Assuntos
Feminino , Humanos , Gravidez , Cuidado Pré-Natal , Revelação da Verdade , Atitude do Pessoal de Saúde , Relações Médico-Paciente , Diagnóstico Pré-NatalRESUMO
Patients presenting with active systemic lupus erythematosus (SLE) manifestations may exhibit distinct pathogenetic features in relation to inactive SLE. Also, cDNA microarrays may potentially discriminate the gene expression profile of a disease or disease variant. Therefore, we evaluated the expression profile of 4500 genes in peripheral blood lymphocytes (PBL) of SLE patients. We studied 11 patients with SLE (seven with active SLE and four with inactive SLE) and eight healthy controls. Total RNA was isolated from PBL, reverse transcribed into cDNA, and postlabeled with Cy3 fluorochrome. These probes were then hybridized to a glass slide cDNA microarray containing 4500 human IMAGE cDNA target sequences. An equimolar amount of total RNA from human cell lines served as reference. The microarray images were quantified, normalized, and analyzed using the R environment (ANOVA, significant analysis of microarrays, and cluster-tree view algorithms). Disease activity was assessed by the SLE disease activity index. Compared to the healthy controls, 104 genes in active SLE patients (80 repressed and 24 induced) and 52 genes in nonactive SLE patients (31 induced and 21 repressed) were differentially expressed. The modulation of 12 genes, either induced or repressed, was found in both disease variants; however, each disease variant had differential expression of different genes. Taken together, these results indicate that the two lupus variants studied have common and unique differentially expressed genes. Although the biological significance of the differentially expressed genes discussed above has not been completely understood, they may serve as a platform to further explore the molecular basis of immune deregulation in SLE.
Assuntos
Perfilação da Expressão Gênica , Lúpus Eritematoso Sistêmico/genética , Linfócitos/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Adulto , Análise por Conglomerados , Feminino , Humanos , Lúpus Eritematoso Sistêmico/sangue , Lúpus Eritematoso Sistêmico/patologia , Linfócitos/citologia , Pessoa de Meia-Idade , Adulto JovemRESUMO
Cyclosporin A (CsA) is a potent immunosuppressant that has been extensively used to attenuate patient immune response following organ transplantation. The molecular biological mechanism of CsA has been extensively investigated in human T cells, and it has been shown to involve modulation of the intracellular calcineurin pathway. However, it is plausible that this chemical immunosuppressant certainly up- or down-regulate many other biochemical pathways of immune cells. In the present study, we used the cDNA microarray method to characterize the gene expression profile of human peripheral blood mononuclear cells (PBMC) treated in vitro with CsA and controls. The CsA treated PBMC displayed statistically significant induction of genes involved in the control of cell-cycle regulation (TRRAP), apoptosis/DNA repair (PRKDC, MAEA, TIA1), DNA metabolism/response to DNA damage stimulus (PRKDC, FEN1), transcription (NR4A2, THRA) and cell proliferation (FEN1, BIN1), whose data have permitted identification of target genes involved in CsA immunosuppression.
Assuntos
Apoptose/genética , Ciclo Celular/genética , Ciclosporina/farmacologia , Reparo do DNA/genética , Leucócitos Mononucleares/efeitos dos fármacos , Leucócitos Mononucleares/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos , Perfilação da Expressão Gênica , Regulação da Expressão Gênica/efeitos dos fármacos , HumanosRESUMO
T-cell differentiation and induction of tolerance to self-antigens occurs mainly in the thymus. Thymic stromal cells, specifically medullary thymic epithelial cells, express a diverse set of genes encoding parenchymal organ-specific proteins. This phenomenon has been termed promiscuous gene expression (PGE) and has been implicated in preventing organ-specific autoimmunity by inducing T-cell tolerance to self antigens. Early thymopoiesis and the critical factors involved in T-cell differentiation can be reproduced in vitro by murine fetal thymus organ culture (FTOC), which mimics the natural thymic microenvironment. To evaluate the occurrence of PGE in FTOC, gene expression profiling during in vitro thymic development in BALB/c mice was performed using a set of nylon cDNA microarrays containing 9216 sequences. The statistical analysis of the microarray data (sam program) revealed the temporal repression and induction of 57 parenchymal and seven lymphoid organ-specific genes. Most of the genes analysed are repressed during early thymic development (15-17 days post-coitum). The expression of the autoimmune regulator (AIRE) gene at 16 days post-coitum marks the onset of PGE. This precedes the induction of parenchymal organ genes during the late developmental phase at 20 days post-coitum. The mechanism of T-cell tolerance induction begins during fetal development and continues into adulthood. Our findings are significant because they show a fine demarcation of PGE onset, which plays a central role in induction of T-cell tolerance.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Timo/embriologia , Animais , Diferenciação Celular/genética , Diferenciação Celular/imunologia , Mapeamento Cromossômico , Desenvolvimento Fetal/genética , Perfilação da Expressão Gênica/métodos , Camundongos , Camundongos Endogâmicos BALB C , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Técnicas de Cultura de Órgãos , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Tolerância a Antígenos Próprios/genética , Timo/imunologia , Timo/metabolismoRESUMO
Systemic lupus erythematosus (SLE) is a prototype of autoimmune disease which arises from interactions between susceptibility genes and environmental factors. Despite the heterogeneous manifestations in this disease, all SLE patients present plasma autoantibodies recognizing nuclear components. Thus, auto reactive B cells represent key effectors to be investigated. Human linkage analysis is providing the localization of susceptibility loci distributed in chromosomes contributing to elucidate the manner in which interactions between these loci mediate SLE pathogenesis. We associate the cDNA microarray technology to investigate the differential gene expression of CD19(+) B cells with genetic linkage data. Bioinformatics programs served to evidentiate the differentially expressed sequences and the design of the microarray allowed hierarchical clustering of patients and controls. Sequencing allowed the identification of 8 new gene products differentially expressed (ESTs) that were co-localized in SLE or other autoimmune diseases susceptibility loci on chromosome 1p21, 2q21, 13q33, 16p12.1 and 16q12.1. These findings strongly suggest that chromosomal regions previously identified as SLE susceptibility loci are in fact transcribed in CD19(+) B cells of patients. In this review, we delineate a new possibility for the use of cDNA microarrays in studies focusing the control of gene expression of disease susceptibility loci identified by genetic linkage.
Assuntos
Antígenos CD19/genética , Lúpus Eritematoso Sistêmico/genética , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Antígenos CD19/imunologia , Expressão Gênica , Ligação Genética , Predisposição Genética para Doença , Humanos , Lúpus Eritematoso Sistêmico/imunologiaRESUMO
BACKGROUND: Methods for the extraction of DNA from filamentous fungi are frequently laborious and time consuming because most of the available protocols include maceration in liquid nitrogen after the mycelium has been grown in a liquid culture. This paper describes a new method to replace those steps, which involves the growth of the mycelium on cellophane disks overlaid on solid medium and the use of glass beads for cell wall disruption. RESULTS: Extractions carried out by this method provided approximately 2 microg of total DNA per cellophane disk for the filamentous fungus Trichoderma reesei. To assess the DNA's quality, we made a PCR (Polymerase Chain Reaction) amplification of a gene introduced by a transformation in this fungus's genome (hph gene), with successful results. We also confirmed the quality of the DNA by the use of Southern blotting to analyze the presence of the same gene, which was easily detected, resulting in a sharply defined and strong band. CONCLUSIONS: The use of this method enabled us to obtain pure DNA from Trichoderma reesei, dispensing with the laborious and time-consuming steps involved in most protocols. The DNA obtained was found to be suitable for PCR and Southern blot analyses. Another advantage of this method is the fact that several samples can be processed simultaneously, growing the fungus on multiple well cell culture plates. In addition, the absence of maceration also reduces sample handling, minimizing the risks of contamination, a particularly important factor in work involving PCR.