What analysis of maternal serum may predict chromosomal abnormalities in the fetus?

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Summary

Background

Maternal serum Lamin A (LMNA) was reported to have potential diagnostic value in the prenatal diagnosis of congenital heart disease (CHD). In this study, we aimed to further assess the prognostic value of maternal serum LMNA in predicting adverse pregnancy outcomes.

Methods

A prospective screening study was performed on singleton pregnancies at 15–18 weeks of gestation. After a routine test for alpha fetoprotein (AFP), chorionic gonadotropin (hCG), and unconjugated estriol (uE3), serum LMNA levels were measured. Serum LMNA levels were then converted into multiples of the median (MoM). The median MoM values for adverse pregnancy outcomes were compared with those in normal pregnancies. For diseases with differential LMNA expression in the prospective study, another case-control cohort was recruited. The diagnostic value of LMNA in these diseases was further evaluated.

Findings

Between January 1, 2017 and June 30, 2018, a total of 2906 singleton pregnancies were recruited. Of the 2,906 cases, 2711 had data available for analysis. Congenital structural abnormalities, chromosomal abnormalities, and obstetric complications were observed in 152 (5·6%), 15 (0·6%), and 278 (10·3%) patients, respectively. LMNA was downregulated in pregnancies with fetal CHD, fetal neural tube defects (NTD), and preeclampsia (PE). The case-control study cohort included 256 CHD, 60 NTD, 67 PE, and 400 normal pregnancies. The areas under the curve for the prenatal diagnoses of CHD, NTD, and PE were 0·875, 0·871, and 0·816, respectively.

Interpretation

Maternal serum LMNA was found to be a potential biomarker for the prenatal diagnosis of fetal CHD, NTD, and PE.

Funding

National Key Research and Development Program, National Natural Science Foundation of China, LiaoNing Revitalization Talents Program, National Natural Science Foundation of Liaoning, and 345 Talent Project of Shengjing Hospital.

Keywords

LMNA

Serum biomarker

Congenital heart defects

Neural tube defects

Preeclampsia

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Article Sections

Pregnant women of all ages should be offered screening and invasive diagnostic testing for chromosomal abnormalities before 20 weeks’ gestation. New developments in screening methods have increased the number of options for patients. Diagnostic options include chorionic villus sampling in the first trimester and amniocentesis in the second trimester. Screening options in the first trimester include nuchal translucency testing in combination with measurement of pregnancy-associated plasma protein A and human chorionic gonadotropin. Nuchal translucency testing alone is not as effective. Screening options in the second trimester include serum screening using triple or quadruple screening, and ultrasonography. Patients may also choose a combination of first- and second-trimester screening in an integrated, stepwise sequential, or contingent sequential fashion. These options include an analysis of pregnancy-associated plasma protein A, with or without nuchal translucency testing, in combination with quadruple screening. An integrated test with nuchal translucency testing is the most effective method for women who present in the first trimester. If nuchal translucency testing is unavailable, the maternal serum-integrated test is safest and most effective. For women who do not present until the second trimester, the quadruple screen is recommended. Comprehensive counseling should be available to all pregnant women. Specific screening tests will depend on availability of the procedure and patient preference.

Screening for fetal chromosomal abnormalities is an essential part of antenatal care. Historically, maternal age was the determinant of risk. Women older than 35 years at the time of delivery were offered genetic counseling and amniocentesis because of procedure-related loss rates. However, only 20 percent of infants with Down syndrome (trisomy 21) are born to women older than 35 years.1 With the advent of maternal serum alpha-fetoprotein (AFP) testing in the mid-1980s, women younger than 35 years had an option for antenatal diagnosis.2 In the past two decades, additional tests have been shown to increase the detection rate of chromosomal abnormalities while maintaining a low false-positive rate. This gives pregnant women of all ages the opportunity to undergo screening or invasive diagnostic testing before 20 weeks’ gestation. Table 1 provides a glossary of terms related to fetal screening.3–6

Invasive Diagnostic Testing

CHORIONIC VILLUS SAMPLING

Chorionic villus sampling (CVS) for genetic diagnosis is performed between 10 and 13 weeks’ gestation. It allows for sampling of the placental tissue. There are two approaches to CVS: transabdominal and transcervical. Transcervical CVS has a higher incidence of spontaneous pregnancy loss, but it is the preferred method if the placenta is posterior or if the bowel inhibits a transabdominal approach. The main advantage of CVS is early and definitive chromosomal analysis.3 However, it is an invasive test that carries a risk of pregnancy loss varying from 0.6 to 4.6 percent.4

CVS has an operator-dependent learning curve and may not be available in every community.4 One study reported a 0.8 percent greater loss rate with CVS than with amniocentesis, and a cytogenetic diagnosis rate of 97.8 percent.7 Although there have been concerns that CVS leads to limb reduction defects, current data suggest that when performed between 10 and 13 weeks’ gestation, there is no significant difference from the incidence in the general population (i.e., six in 10,000). CVS performed before 10 weeks’ gestation increases the risk of limb reduction defects to 1 to 2 percent.4

AMNIOCENTESIS

Amniocentesis for genetic diagnosis is typically performed between 16 and 18 weeks’ gestation, which is when the procedure is safest.8 However, it can be performed from 14 to 20 weeks. During amniocentesis, a needle is inserted into the amniotic sac using ultrasound guidance, and amniotic fluid is aspirated.3 The fetal loss rate associated with amniocentesis is often reported to be 1 percent,9 although it has been reported to be as low as one in 370.10 The cytogenetic diagnosis rate is reported to be 99.4 percent.7 Complications are uncommon, but may include vaginal spotting, amniotic fluid leakage, chorioamnionitis, failure of fetal cells to grow in culture, fetal needle injury, and fetal loss.3

First-Trimester Screening

NUCHAL TRANSLUCENCY

Nuchal translucency refers to an ultrasonographic sonolucency in the posterior fetal neck.11 The measurement is gestational-age dependent; on average, it increases 15 to 20 percent per week. Measuring nuchal translucency requires specialized training and certification to learn the standardized technique.12 Having specific measurement guidelines helps maintain the detection rate of Down syndrome.5 Using only nuchal translucency testing, there is a detection rate of approximately 70 to 71 percent for Down syndrome, with a 3.5 to 5 percent false-positive rate.13,14 Increased nuchal translucency of greater than 3.5 mm is associated with major congenital heart defects, defects of the great vessels, fetal malformations, dysplasias, deformations, disruptions, and genetic syndromes.15–17 Abnormal nuchal translucency may lead to an earlier diagnosis of congenital heart defects.18 However, if aneuploidy is excluded and targeted ultrasonography at 20 to 22 weeks’ gestation is normal, there is no significantly increased risk of adverse outcome.17

COMBINED SCREENING

Nuchal translucency testing should be combined with serum measurements of pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG) during the first trimester to improve the detection rate of Down syndrome to 78.7 to 89 percent, with a false-positive rate of 5 percent.19–22 Low levels of both markers are associated with adverse pregnancy outcomes, such as spontaneous loss before fetal viability, gestational hypertension, preeclampsia, preterm premature rupture of membranes, placental abruption, preterm birth, low birth weight, and stillbirth.23,24

In women younger than 35 years, combined screening is equivalent to quadruple screening for the detection of Down syndrome. In women older than 35 years, combined screening detects approximately 90 percent of Down syndrome, but the false-positive rate increases to 16 to 22 percent. For all women, the detection rate of combined screening for trisomy 18 is 90 percent, with a false-positive rate of 2 percent.5 First-trimester screening affords the advantage of early diagnosis so that confirmatory testing can be undertaken. If desired, termination can be performed at an early gestational age, allowing greater privacy and less risk. The American College of Obstetrics and Gynecology (ACOG) recommends that first-trimester screening should be offered to patients only if appropriate sonographic training, ongoing quality assurance, sufficient comprehensive counseling, and diagnostic testing are available.25 Most laboratories that offer serum analysis require certification and ongoing quality assurance by the ultrasonographer.5

Second-Trimester Screening

SERUM SCREENING

Second-trimester maternal serum testing includes the triple and quadruple screens. After the introduction of maternal serum AFP testing in the mid-1980s, hCG and unconjugated estriol testing were added, resulting in the triple screen.26 The addition of inhibin A testing to the triple screen yielded the quadruple screen.27,28 Serum screening is calculated using an algorithm based on the age, race, weight, and diabetic status of a patient. As early as 1996, the Agency for Healthcare Research and Quality recommended that all pregnant women be offered maternal serum screening for Down syndrome and neural tube defects if adequate counseling and follow-up are available.29,30 Current data suggest that with a fixed screen-positive rate of 5 percent, the detection rate for Down syndrome is 69 percent for the triple screen and 81 percent for the quadruple screen.5 Women with isolated elevated maternal serum AFP should be followed closely because they are at increased risk of poor pregnancy outcomes.5

ULTRASONOGRAPHY

Ultrasonography may also be used for screening in the second trimester, either alone or as an adjunct to maternal serum testing. Targeted imaging for fetal anomalies can help determine whether invasive testing should be persued.11,31 Various markers of fetal chromosomal abnormalities may be detected by ultrasonography (e.g., facial cleft, micrognathia, atrioventricular septal defects, echogenicbowel).32–34 There have been attempts to identify patterns of sonographic findings and their associations.35,36 A 2005 study reported that in the absence of any marker for Down syndrome, the risk of having an affected fetus is reduced 60 to 80 percent, because 75 percent of fetuses with Down syndrome can be detected using ultrasonography.37

Another study found a similar sensitivity rate of 79.9 percent, with a false-positive rate of 6.7 percent, when measuring nuchal fold thickness and proximal long bone length.38 Nuchal fold thickening does not connote the risk level of Down syndrome found with nuchal translucency. However, women with isolated nuchal fold thickening with normal ultrasonography and normal karyotype should be followed closely because they are at increased risk of poor pregnancy outcomes.5 When performed in combination with the quadruple screen, ultrasound sensitivity approaches 90 percent, with a 3.1 percent false-positive rate.38 Other studies have placed the detection rate of ultrasonography at a more modest rate of 35 to 47 percent.39,40

In 1996, the U.S. Preventive Services Task Force found insufficient evidence to recommend for or against routine second-trimester ultrasonography in low-risk pregnancies.41 It noted that ultrasonography in pregnancy has become common, and that updating the recommendation would have limited potential impact on clinical practice. A meta-analysis of 56 studies analyzing 1,930 fetuses with Down syndrome and 130,365 unaffected fetuses found that using ultrasonographic markers alone as a basis to offer amniocentesis would result in a decrease in perinatal detection of Down syndrome.42

Combined First- and Second-Trimester Screening

Further efforts to improve detection rates of aneuploidy with antenatal screening led to the combining of existing first- and second-trimester screening. With combined testing, detection rates are improved to 92 to 96 percent, with false-positive rates of 5 percent.43,44

INTEGRATED SCREENING

Integrated screening involves PAPP-A and nuchal translucency testing in the first trimester and the quadruple screen in the second trimester. After the first trimester tests are completed, the results are held until the quadruple screen is performed. A single risk determination is made using all available data and the patient’s age-associated risk. Integrated serum screening uses PAPP-A and quadruple screening without nuchal translucency, if it is unavailable.

STEPWISE SEQUENTIAL SCREENING

Stepwise sequential screening combines PAPP-A and nuchal translucency testing with an age-associated risk to provide a risk determination in the first trimester. If the patient is at increased risk based on results of the first trimester PAPP-A and nuchal translucency testing, she may undergo invasive diagnostic testing or await the triple or quadruple screen in the second trimester for revised risk determination. If the patient chooses to undergo second-trimester serum testing, a second risk determination is made with all available data.

CONTINGENCY SCREENING

Contingency screening also involves PAPP-A and nuchal translucency testing with an age-associated risk to provide a risk determination in the first trimester. However, with contingency testing, the risk determination is stratified. If the risk is above a certain cut-off, invasive diagnostic testing is offered. If the risk is below a second cut-off, the patient is told that no further testing is required. If the patient’s risk determination falls between these two cut-offs, then second-trimester maternal serum screening is advised.24,44,45

Recommendations

New guidelines have been released in response to the availability of these testing strategies. Table 2 summarizes available testing options.5,7–9,13,14,20,23,37,39,40,43,46–49 The British Medical Association recommends the integrated test or the serum-integrated test if nuchal translucency testing is not available.50,51 For women presenting in the second trimester, the quadruple screen is recommended. For first-trimester screening, the combined test is recommended. The triple screen or nuchal translucency testing alone are not recommended. The National Collaborating Centre for Women’s and Children’s Health makes similar recommendations.52 It acknowledges that the integrated test is cost-effective and results in the fewest losses of normal fetuses. However, because of concerns about the practicality of the integrated test and because most women prefer a one-stage test, it recommends combined testing in the first trimester and the quadruple or triple screen in the second trimester.52

ACOG released its most recent recommendations in January 2007, stating that the combined test is comparable to the quadruple test for screening.5 The recommendations also state that nuchal translucency testing is less effective than the combined test, and it requires training, standardization, and ongoing quality assessment. Women who are identified as high risk with first-trimester screening should be offered invasive diagnostic testing and genetics counseling. Women who elect to undergo the combined test alone still need maternal serum AFP testing for neural tube defects in the second trimester. Additional recommendations include offering all women screening and invasive diagnostic testing before 20 weeks’ gestation.

Advantages of antenatal screening include increasing the odds of identifying an abnormal fetus and reducing the number of invasive diagnostic tests and procedure-related losses of normal fetuses. The disadvantage of screening is that not all aneuploid fetuses are identified with screening. Because of this, all patients have the option of proceeding directly with invasive testing. ACOG notes that integrated testing is better than first-trimester screening alone, and that if nuchal translucency testing is unavailable, serum-integrated testing is a useful option.5 Abnormal second-trimester ultrasonography warrants counseling and offering a diagnostic procedure. If the nuchal translucency is greater than or equal to 3.5 mm, invasive diagnostic testing should be offered, and if it is normal, targeted ultrasonography, fetal echocardiography, or both should be offered.

First- or second-trimester testing can be performed on multiple gestations, but it is less sensitive because the maternal serum value may represent an average of normal and abnormal fetuses, thus masking the abnormal result. Nuchal translucency testing for multiple gestations is feasible, with invasive diagnostic testing to follow if indicated and desired by the patient. First- and second-trimester screening for Down syndrome is not indicated unless it is offered as part of integrated, stepwise, or contingent testing.5

Based on these recommendations, all pregnant women should be offered screening for aneuploidy. It is important to review which tests are locally available.5 Patients may benefit from the expertise of a genetics counselor because comprehensive counseling can be difficult during a short office visit. Understanding patients’ worldviews is essential, as is discussing early diagnosis and options for termination, and recognizing that not all patients will desire screening. Minimizing the risk of the screening and maximizing safety is also crucial.1,44,46 With the advent of first-trimester options, patients will need to choose early and be comfortable with their choice.

What tests can be used to detect abnormality in the fetus?

An ultrasound creates pictures of the baby. This test is usually completed around 18–20 weeks of pregnancy. The ultrasound is used to check the size of the baby and looks for birth defects or other problems with the baby.

How can we test for chromosomal abnormalities in the developing fetus?

Four main types of screening tests for chromosome abnormalities are available: Early risk assessment (with or without “sequential screening”), quadruple screen, cell-free DNA analysis (cfDNA), and full fetal survey. at the “nuchal translucency.” This refers to fluid behind the neck of a fetus.

What are three tests used to detect chromosomal abnormalities?

Amniocentesis, chorionic villus sampling (CVS) and ultrasound are the three primary procedures for diagnostic testing. Amniocentesis — Amniocentesis is used most commonly to identify chromosomal problems such as Down syndrome.