Approach and Management of Pregnancies with Risk Identified by Non-Invasive Prenatal Testing

This study represents our second investigation into NIPT, involving a more extensive patient cohort with a specific emphasis on the high-risk group. The high-risk group was subsequently divided into two further groups to compare confirmed cases versus unconfirmed via direct methods. The methodology encompassed the analysis of 1400 consecutive cases from a single genetic center in western Romania, where NIPT was used to assess the risk of specific fetal chromosomal abnormalities. All high-risk cases underwent validation through direct analysis of fetal cells obtained via invasive methods, including chorionic villus sampling and amniocentesis. The confirmation process utilized QF-PCR, karyotyping, and SNP-Array methods customized to each case. Results: A high risk of aneuploidy at NIPT was identified in 36 out of 1400 (2.57%) cases and confirmed in 28 cases. The study also detected an increased risk for copy number variations (CNVs) in 1% of cases, confirmed in two instances involving one large microdeletion and one large microduplication. Trisomy 21 was the exclusive anomaly where NIPT confirmed all cases with identified risk. High-risk NIPT results which were not validated by invasive methods, were classified as false positives; parents in these cases determined to continue the pregnancy. In conclusion, NIPT can serve as a screening method for all pregnancies; however, in high-risk cases, an invasive confirmation test is strongly recommended.

Determinant of Prenatal Diagnostic Testing among Women with Increased Risk of Fetal Aneuploidy and Genetic Disorders

OBJECTIVE

 This study aimed to assess factors that influence patients' decisions in accepting prenatal diagnostic testing following genetic counseling for increased risk of fetal aneuploidy.

METHODS

 This is a retrospective cohort study of women at increased risk of fetal aneuploidy and genetic disorders who had genetic counseling from January 2012 to December 2016 at a single academic center. Demographics, indications for genetic counseling, and rates of diagnostic testing were collected and compared between those who accepted diagnostic testing and those who chose cell free DNA. The variables were analyzed using Chi-square, Fisher's exact test, and multiple logistic regression.

RESULT

 Of the 2,373 pregnant women who underwent genetic counseling for increased risk of fetal aneuploidy and genetic disorders during the study period, 321 women had diagnostic testing (13.5%). Women at 35 years and older accepted diagnostic testing more than women younger than 35 years (20.7 vs. 11.5%, p < 0.001). Asian women accepted diagnostic testing at 27.7% more than white, non-Hispanic Black, and Hispanic women at 18.0, 12.1, and 11.7%, respectively, p = 0.002. Number of indications for genetic counseling influenced the likelihood of accepting diagnostic testing. Women with one indication had 11.5% acceptance of diagnostic testing, and with two and three indications, it was 17.0 and 29.2%, respectively. The commonest indication for diagnostic testing was cystic hygroma (risk ratio [RR] = 7.5, 95% confidence interval [CI]: 3.12-8.76 p < 0.001). The relative risk of diagnostic testing for fetuses with shortened long bones, femur and humerus, thickened nuchal fold, echogenic bowel, single umbilical artery, and increased nuchal translucency were 4.0, 3.3, 3.1, 2.7, and 2.7, respectively. Abnormal serum analyte alone was associated with less acceptance of diagnostic testing (RR = 0.8, 95% CI: 0.7-0.96, p = 0.017).

CONCLUSION

 Age, race, ethnicity, and cumulative number of indications for genetic counseling influenced acceptance of diagnostic testing in at-risk women of fetal aneuploidy and genetic disorders.

KEY POINTS

· Genetic counseling.. · Fetal aneuploidy.. · Genetic disorders.. · Prenatal diagnostic testing. Prenatal diagnostic testing in women with increased risk of fetal aneuploidy and genetic disorders..

The relationship of maternal polymorphisms of genes related to meiosis and DNA damage repair with fetal chromosomal stability

OBJECTIVES

To evaluate the association between maternal polymorphisms of NANOS3 rs2016163, HELQ rs4693089, PRIM1 rs2277339, TLK1 rs10183486, ERCC6 rs2228526, EXO1 rs1635501, DMC1 rs5757133, and MSH5 rs2075789 and fetal chromosomal abnormality.

METHODS

This retrospective case-control study included 571 women with fetal chromosome abnormalities (330 pregnant women diagnosed with fetal aneuploidy, 241 with fetal de novo structural chromosome pregnancy) and 811 healthy pregnant women between January 2018 and April 2022. All the above polymorphisms were tested using SNaPshot.

RESULTS

All the eight polymorphisms were analyzed for genotypes, alleles, under dominant and recessive genetic models. Significant distribution differences of TLK1 rs10183486 in fetal chromosome structural abnormality were found between the case group and control subjects who were <35 years of age [Genotype: p=0.029; Dominant: OR (95 %CI)=0.46 (0.25-0.82), p=0.01 and allele: OR (95 %CI)=0.47 (0.27-0.82), p=0.01 respectively], while no difference was found in the recessive model [OR (95 %CI)=2.49 (0.31-20.40), p=0.39]. In advanced age subgroups for fetal aneuploidy, significant differences were found in genotypes analysis of PRIM1 rs2277339 (p=0.008), allele analysis of TLK1 rs10183486 [OR (95 %CI)=0.62 (0.42-0.91), p=0.02]. For the fetal chromosome structural abnormality population, HELQ rs4693089 revealed a significant distribution difference (p=0.01) but not in the allele, dominant and recessive genetic models analysis (p>0.05 individually).

CONCLUSIONS

For older women, maternal PRIM1 rs2277339 and TLK1 rs10183486 polymorphisms may be associated with fetal aneuploidy, while HELQ rs4693089 may be associated with fetal chromosome structural abnormality. Also, carriers of T allele of TLK1 rs10183486 have a lower risk of fetal chromosome structural abnormality in younger women.

Biochemical Screening for Fetal Trisomy 21: Pathophysiology of Maternal Serum Markers and Involvement of the Placenta

It is now well established that maternal serum markers are often abnormal in fetal trisomy 21. Their determination is recommended for prenatal screening and pregnancy follow-up. However, mechanisms leading to abnormal maternal serum levels of such markers are still debated. Our objective was to help clinicians and scientists unravel the pathophysiology of these markers via a review of the main studies published in this field, both in vivo and in vitro, focusing on the six most widely used markers (hCG, its free subunit hCGβ, PAPP-A, AFP, uE3, and inhibin A) as well as cell-free feto-placental DNA. Analysis of the literature shows that mechanisms underlying each marker's regulation are multiple and not necessarily directly linked with the supernumerary chromosome 21. The crucial involvement of the placenta is also highlighted, which could be defective in one or several of its functions (turnover and apoptosis, endocrine production, and feto-maternal exchanges and transfer). These defects were neither constant nor specific for trisomy 21, and might be more or less pronounced, reflecting a high variability in placental immaturity and alteration. This explains why maternal serum markers can lack both specificity and sensitivity, and are thus restricted to screening.

Current Perspectives of Prenatal Cell-free DNA Screening in Clinical Management of First-Trimester Septated Cystic Hygroma

First-trimester septated cystic hygroma occurs in approximately 1 in 268 pregnancies and has long been associated with a markedly increased risk of fetal aneuploidy and, among euploid fetuses, an increased risk of structural anomalies primarily affecting the cardiac and skeletal systems. Invasive prenatal diagnosis – chorionic villus sampling and/or amniocentesis – encompasses the time-honored clinical tools for the next step in management following prenatal sonographic diagnosis of first-trimester septated cystic hygroma. Currently, prenatal cell-free DNA (cfDNA) screening for fetal aneuploidy with select microdeletions is gradually replacing the considerably less sensitive, and labor-intensive combined first-trimester screening. These new technologies have opened potential new venues in the clinical management of this ominous late first-trimester sonographic diagnosis. Advances in cfDNA technologies are now permitting detection of chromosomal copy number variants (CNV) larger than 7Mb across genome and select serious single-gene disorders (mainly impacting skeletal and neurological development), affecting quality of life and may benefit from medical and/or surgical management. This commentary will address the available non-invasive prenatal screening technologies, which clearly enhance immediate genetic analysis modalities applicable in the presence of the complex sonographic finding of first-trimester septated cystic hygroma.

Noninvasive prenatal testing and maternal obesity: A review

Noninvasive prenatal testing (NIPT) has become a popular screening test for the most common fetal aneuploidies. The performance of NIPT is affected by several factors including maternal obesity, which results in a greater rate of no-calls for obese pregnant women. Guidelines regarding NIPT in prenatal screening have been published, but with few and divergent recommendations on the issue. We aimed to review the medical literature, guidelines from scientific societies and information material from commercial NIPT providers on no-calls and maternal obesity. We systematically identified medical literature and guidelines from scientific societies using the database MEDLINE. Information material from commercial NIPT providers was found via a systematic search on Google.com. Nine medical studies investigating the association between maternal obesity and NIPT no-calls were included. They all showed the same trend: increasing no-call rate with increasing maternal obesity. The no-call rate ranged from 0% to 4.2% for women with body mass index (BMI) 18.5-24.9 and from 5.4% to 70.1% for women BMI ≥40. We identified 17 scientific societies with guidelines and 13 commercial NIPT providers. All were checked for information material on no-calls and maternal obesity. To allow comparison, all guidelines were examined to answer the same three predefined questions. Of the 17 included scientific societies, 13 (76.5%) mentioned the association between maternal obesity and NIPT no-calls, two (11.8%) specified weight limits and three (17.6%) advised against NIPT for severely obese pregnant women. None of the 13 commercial NIPT providers provided specific recommendations, but four (30.8%) cite maternal obesity as a potential cause for a no-call. Because of the increasing number of patients in this group, we advocate updated recommendations to guide decision making in prenatal screening for obese pregnant women.

Non-invasive prenatal testing for detection of trisomy 13, 18, 21 and sex chromosome aneuploidies in 8594 cases

OBJECTIVES

Cell-free fetal DNA has been widely used in prenatal genetic testing during recent years. We explored the feasibility of non-invasive prenatal testing (NIPT) for analysis of common fetal aneuploidies among pregnancies in northwest China.

MATERIAL AND METHODS

A total of 8594 maternal blood samples were collected from October 2014 to December 2017 in the Department of Obstetrics and Gynecology at the First Affiliated Hospital of the Air Force Medical University. Cases with positive screening results by NIPT detection were validated using karyotype analysis.

RESULTS

Of 8594 clinical pregnancies, 88 had positive NIPT results and 78 of 88 (88.6%) positive NIPT results were shown to be false-positive by amniotic fluid puncture and chromosome karyotyping analysis. There were 44 cases (49.44%) with trisomy 21, 18, and 13 syndromes (30 cases of trisomy 21, 9 cases of trisomy 18, and 5 cases of trisomy 13). There were 44 cases (50.56%) with sex chromosome abnormalities, including 11 cases with Turner syndrome (45, X), 17 cases with Triple X syndrome (47, XXX), 2 cases with Klinefelter syndrome (47, XXY), and 14 cases with 47, XYY syndrome (47, XYY).

CONCLUSIONS

The accuracy, specificity, high efficiency, and acceptance of NIPT can effectively avoid birth defects and improve the quality of the birth population. We should deepen mining and analysis of the clinical data and explore ways to use NIPT. It is recommended that the NIPT guidelines be extended to low-risk patients to further explore the impact of a significant increase in screening.

Sequencing shorter cfDNA fragments improves the fetal DNA fraction in noninvasive prenatal testing

BACKGROUND

Sequencing cell-free DNA in maternal plasma is an effective noninvasive prenatal testing technique that has been used in fetal aneuploidy screening worldwide. However, its clinical application is limited by the low fetal fraction (<4%) of cell-free DNA in many singleton pregnancies, which usually results in screen failures or no calls. In addition, dizygotic twin contributions of cell-free DNA into the maternal circulation can vary by 2-fold, complicating the quantitative diagnosis of fetal aneuploidy.

OBJECTIVE

We performed semiconductor sequencing of shorter fragments (107-145 bp) of circulating cell-free DNA to improve the fetal DNA fraction at lower uniquely mapped reads (1-8.5 MB) to reduce the probability of no calls.

STUDY DESIGN

We identified 2903 plasma samples from pregnant women, including 86 dizygotic twin pregnancy, that were collected at a single prenatal diagnostic center between October 2015 and July 2018. Size-selection noninvasive prenatal testing for fetal aneuploidy was applied to 2817 plasma samples (1409 male and 1408 female fetuses) and 86 dizygotic twins using noninvasive prenatal testing with and without size selection. Shorter fragment size was the key factor affecting fetal fraction in multivariable linear regression models as well as to validate the accuracy of the size selection for noninvasive prenatal testing.

RESULTS

Analysis of 1409 male fetuses by multivariable linear regression showed that maternal age, body mass index, number of pregnancies, average cell-free DNA size, maternal plasma cell-free DNA concentration, library concentration, and multiple gestation were negatively correlated with fetal fraction. Conversely, gestational age and uniquely mapped reads were positively correlated with fetal fraction. Compared with ≤120 bp cell-free DNA fragments, mean fetal fraction differences were -3.57% (95% confidence interval, -5.95% to -1.19%), for 121-130 bp, -9.52% (95% confidence interval, -11.89% to -7.14%) for 131-140 bp, and -14.47% (95% confidence interval, -18.37% to -10.58%) for ≥141 bp (P_trend < .0001). These results were statistically significant after multivariable adjustments in models for fetal fraction. Meanwhile, results from 86 dizygotic twins showed that the size selection increased the fetal fraction by ∼3.2-fold, with 98.8% of samples reaching a fetal fraction >10%. Improved detection accuracy was also achieved.

CONCLUSION

Sequencing shorter cell-free DNA fragments is a reasonable strategy to reduce the probability of no calls results because of low fetal fraction and should be recommended to pregnant subjects.

A Comprehensive Approach to Care of Women of Advanced Maternal Age

Advanced maternal age, historically defined as ages 35 years and older, is used to describe the later years in the female reproductive life span when rates of adverse pregnancy outcomes increase. The preconception period represents an opportunity to ensure the use of safe medications and optimize care for medical comorbidities. Routine prenatal care should be augmented with counseling on fetal aneuploidy with a detailed anatomic survey. Surveillance for preterm labor and preeclampsia is recommended. Growth assessment and antepartum testing for specific women are advised, particularly those ages 40 years and older and those with select medical problems. Despite an increased incidence of complications, most women of advanced maternal age will have normal pregnancies and will benefit from the compassionate care provided by midwives, advanced practice registered nurses (including nurse practitioners and clinical nurse specialists), and perinatal nurses.

Umbilical artery pulsatility index and half-peak systolic velocity deceleration time in fetuses with trisomy 21

Objective: To analyze placental vascular resistance and the role of placental insufficiency in the etiology of reduced fetal growth in fetuses with trisomy 21 as determined by umbilical artery (UA) Doppler velocimetry.Methods: Second- and third-trimester UA Doppler ultrasound studies were performed in fetuses with trisomy 21 at the time of clinically indicated obstetric ultrasound assessment. The UA pulsatility index (PI) and half-peak systolic velocity deceleration time (hPSV-DT) were measured and recorded. Perinatal outcome was reviewed and the results from UA Doppler velocimetry were compared with birthweight according to gestational age at the time of the delivery.Results: A total of 60 fetuses with trisomy 21 were studied and information from 147 UA Doppler studies was analyzed. Overall, at least one of the UA PI and hPSV-DT values was abnormal in 82% (n = 49) and 90% (n = 54) of the cases, respectively. The incidence of abnormal UA PI values increased with gestational age from 39% (7/18) before 21 weeks to 78% (18/23) after 35 weeks (p < .05). The increase was even more evident for UA hPSV-DT values from 28% (5/18) before 20 weeks to 91% (21/23) after 35 weeks (p < .01). After exclusion of four fetuses with hydrops or isolated hydrothorax/ascites, 16 (29%) were classified at birth as small for gestational age (SGA), 34 (61%) as adequate for gestational age, and six (11%) as large for gestational age, with a mean birthweight z-score of -0.36. When only considering the last Doppler ultrasound assessment prior to delivery, UA PI and hPSV-DT values were abnormal in 73% (41/56, mean z-score = +1.72) and 82% (46/56; mean z-score = -2.18) of the cases, respectively. Mean gestational age at delivery and birth weight were significantly lower in the group with abnormal compared to normal UA PI and hPSV-DT values. Similarly, the incidence of SGA fetuses was significantly higher in the group with abnormal compared to normal UA PI and hPSV-DT values, with 94 (n = 15) and 100% of the 16 SGA newborn infants having abnormal UA PI and hPSV-DT values prior to delivery, respectively.Conclusions: Trisomy 21 fetuses have a progressively higher incidence of abnormal UA impedance indices throughout pregnancy, which suggests developing placental vascular resistance as the pregnancy progresses. This alteration likely begins around the mid second trimester and increases with gestational age; however, increasing placental vascular resistance seems to produce a discrete decrease in fetal growth, despite severe alteration of the UA Doppler impedance indices. As a general hypothesis, we postulate that trisomy 21 fetuses have increasing placental vascular resistance but there may be some factors that protect these fetuses from severe fetal growth restriction.

Prenatal cell-free DNA screening for fetal aneuploidy in pregnant women at average or high risk: Results from a large US clinical laboratory

BACKGROUND

We evaluated the performance of a cell-free DNA (cfDNA) prenatal screening assay for trisomies 21, 18, and 13, and sex chromosome aneuploidies (SCAs) among a population of pregnant women that included both those at average and high risk.

METHODS

Specimen collection, cfDNA extraction, massively parallel sequencing, and bioinformatics analysis were conducted per laboratory protocol. Assay results, concordance with pregnancy outcomes, and performance characteristics were evaluated.

RESULTS

A total 75,658 specimens from 72,176 individual pregnant women were received. Technical reasons accounted for 288 (0.4% of all received samples) tests not performed. In the final analysis cohort (N = 69,794), 13% of pregnancies were considered at average risk and 87% at high risk. Mean gestational age at specimen collection was 15.1 weeks. Of the 69,794 unique pregnancies, 1,359 (1.9%) had positive test results. Among the results with confirmed outcomes, PPV for trisomies 21, 18, and 13 was 98.1%, 88.2%, and 59.3%, respectively; the PPV was 69.0% for SCAs and 75.0% for microdeletions. Overall, PPV was 87.2%, sensitivity was 97.9%, and specificity was 99.9%.

CONCLUSION

This cfDNA prenatal screening assay provides highly accurate discrimination between affected and unaffected pregnancies among a population of pregnant women at average and high risk for fetal genetic abnormalities.

Analysis of cell-free DNA in maternal blood in screening for aneuploidies: updated meta-analysis

OBJECTIVES

To review clinical validation or implementation studies of maternal blood cell-free (cf) DNA analysis and define the performance of screening for fetal trisomies 21, 18 and 13 and sex chromosome aneuploidies (SCA).

METHODS

Searches of PubMed, EMBASE and The Cochrane Library were performed to identify all peer-reviewed articles on cfDNA testing in screening for aneuploidies between January 2011, when the first such study was published, and 31 December 2016. The inclusion criteria were peer-reviewed study reporting on clinical validation or implementation of maternal cfDNA testing in screening for aneuploidies, in which data on pregnancy outcome were provided for more than 85% of the study population. We excluded case-control studies, proof-of-principle articles and studies in which the laboratory scientists carrying out the tests were aware of fetal karyotype or pregnancy outcome. Pooled detection rates (DRs) and false-positive rates (FPRs) were calculated using bivariate random-effects regression models.

RESULTS

In total, 35 relevant studies were identified and these were used for the meta-analysis on the performance of cfDNA testing in screening for aneuploidies. These studies reported cfDNA results in relation to fetal karyotype from invasive testing or clinical outcome. In the combined total of 1963 cases of trisomy 21 and 223 932 non-trisomy 21 singleton pregnancies, the weighted pooled DR and FPR were 99.7% (95% CI, 99.1-99.9%) and 0.04% (95% CI, 0.02-0.07%), respectively. In a total of 563 cases of trisomy 18 and 222 013 non-trisomy 18 singleton pregnancies, the weighted pooled DR and FPR were 97.9% (95% CI, 94.9-99.1%) and 0.04% (95% CI, 0.03-0.07%), respectively. In a total of 119 cases of trisomy 13 and 212 883 non-trisomy 13 singleton pregnancies, the weighted pooled DR and FPR were 99.0% (95% CI, 65.8-100%) and 0.04% (95% CI, 0.02-0.07%), respectively. In a total of 36 cases of monosomy X and 7676 unaffected singleton pregnancies, the weighted pooled DR and FPR were 95.8% (95% CI, 70.3-99.5%) and 0.14% (95% CI, 0.05-0.38%), respectively. In a combined total of 17 cases of SCA other than monosomy X and 5400 unaffected singleton pregnancies, the weighted pooled DR and FPR were 100% (95% CI, 83.6-100%) and 0.004% (95% CI, 0.0-0.08%), respectively. For twin pregnancies, in a total of 24 cases of trisomy 21 and 1111 non-trisomy 21 cases, the DR was 100% (95% CI, 95.2-100%) and FPR was 0.0% (95% CI, 0.0-0.003%), respectively.

CONCLUSIONS

Screening by analysis of cfDNA in maternal blood in singleton pregnancies could detect > 99% of fetuses with trisomy 21, 98% of trisomy 18 and 99% of trisomy 13 at a combined FPR of 0.13%. The number of reported cases of SCA is too small for accurate assessment of performance of screening. In twin pregnancies, performance of screening for trisomy 21 is encouraging but the number of cases reported is small. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Analysis of cell-free DNA in maternal blood in screening for fetal aneuploidies: updated meta-analysis

OBJECTIVE

To review clinical validation or implementation studies of maternal blood cell-free (cf) DNA analysis and define the performance of screening for fetal trisomies 21, 18 and 13 and sex chromosome aneuploidies.

METHODS

Searches of PubMed, EMBASE and The Cochrane Library were performed to identify all peer-reviewed articles on cfDNA testing in screening for aneuploidies between January 2011, when the first such study was published, and 4 January 2015.

RESULTS

In total, 37 relevant studies were identified and these were used for the meta-analysis on the performance of cfDNA testing in screening for aneuploidies. These studies reported cfDNA results in relation to fetal karyotype from invasive testing or clinical outcome. Weighted pooled detection rates (DR) and false-positive rates (FPR) in singleton pregnancies were 99.2% (95% CI, 98.5-99.6%) and 0.09% (95% CI, 0.05-0.14%), respectively, for trisomy 21, 96.3% (95% CI, 94.3-97.9%) and 0.13% (95% CI, 0.07-0.20) for trisomy 18, 91.0% (95% CI, 85.0-95.6%) and 0.13% (95% CI, 0.05-0.26%) for trisomy 13, 90.3% (95% CI, 85.7-94.2%) and 0.23% (95% CI, 0.14-0.34%) for monosomy X and 93.0% (95% CI, 85.8-97.8%) and 0.14% (95% CI, 0.06-0.24%) for sex chromosome aneuploidies other than monosomy X. For twin pregnancies, the DR for trisomy 21 was 93.7% (95% CI, 83.6-99.2%) and the FPR was 0.23% (95% CI, 0.00-0.92%).

CONCLUSION

Screening for trisomy 21 by analysis of cfDNA in maternal blood is superior to that of all other traditional methods of screening, with higher DR and lower FPR. The performance of screening for trisomies 18 and 13 and sex chromosome aneuploidies is considerably worse than that for trisomy 21.

Awareness of prenatal screening for fetal aneuploidy among pregnant women in Greece

AIM

To estimate the level of awareness of prenatal screening (PS) and explore the underlying demographic, lifestyle and medical history parameters of Greek and non-Greek pregnant women undergoing prenatal diagnosis.

PATIENTS AND METHODS

A structured questionnaire was answered by 354 women at the time of receiving the results of invasive prenatal testing. Summary statistics and multiple logistic regression analyses were performed.

RESULTS

Adequate knowledge of the effectiveness of PS tests was reported by 50.8% of women. Popular press reading was associated with more than 2-fold higher level of awareness [odds ratio (OR)=0.51, p=0.0004]. Inadequate awareness was recorded among pregnant women of non-Greek nationality (OR=2.07, p=0.04), as well as among those also unaware of the effects of smoking during pregnancy (OR=2.39, p=0.004).

CONCLUSION

Pre-gestational prenatal counseling is essential in order to improve knowledge and attitudes of women towards PS and reduce the health gap between different cultural and social groups.

Size-based molecular diagnostics using plasma DNA for noninvasive prenatal testing

Noninvasive prenatal testing using fetal DNA in maternal plasma is an actively researched area. The current generation of tests using massively parallel sequencing is based on counting plasma DNA sequences originating from different genomic regions. In this study, we explored a different approach that is based on the use of DNA fragment size as a diagnostic parameter. This approach is dependent on the fact that circulating fetal DNA molecules are generally shorter than the corresponding maternal DNA molecules. First, we performed plasma DNA size analysis using paired-end massively parallel sequencing and microchip-based capillary electrophoresis. We demonstrated that the fetal DNA fraction in maternal plasma could be deduced from the overall size distribution of maternal plasma DNA. The fetal DNA fraction is a critical parameter affecting the accuracy of noninvasive prenatal testing using maternal plasma DNA. Second, we showed that fetal chromosomal aneuploidy could be detected by observing an aberrant proportion of short fragments from an aneuploid chromosome in the paired-end sequencing data. Using this approach, we detected fetal trisomy 21 and trisomy 18 with 100% sensitivity (T21: 36/36; T18: 27/27) and 100% specificity (non-T21: 88/88; non-T18: 97/97). For trisomy 13, the sensitivity and specificity were 95.2% (20/21) and 99% (102/103), respectively. For monosomy X, the sensitivity and specificity were both 100% (10/10 and 8/8). Thus, this study establishes the principle of size-based molecular diagnostics using plasma DNA. This approach has potential applications beyond noninvasive prenatal testing to areas such as oncology and transplantation monitoring.

Noninvasive prenatal screening by next-generation sequencing

Noninvasive prenatal screening (NIPS) has emerged as a highly accurate method of screening for fetal Down syndrome, with a detection rate and specificity approaching 100%. Challenging the widespread use of this technology are cost and the paradigm shift in counseling that accompanies any emerging technology. The expense of the test is expected to decrease with increased utilization, and well beyond the current NIPS technology, its components (fetal genome measurements, sequencing technology, and bioinformatics) will be utilized alone or in combinations to interrogate the fetal genome. The end goal is simple: to offer patients information early in pregnancy about fetal genomes without incurring procedural risks. This will allow patients an opportunity to make informed reproductive and pregnancy management decisions based on precise fetal genomic information.