Prenatal diagnosis and multiple pregnancy

Fetal Screening for Chromosomal Abnormalities

With more and more reproductive-aged women opting to pursue genetic screening during pregnancy, health care professionals must understand the variety of testing options available as well as the advantages and limitations of each testing option. Presently, no single screening test is universally believed to be superior because the combination of the specific test and the population being tested determines the range of potential identifiable conditions as well as the positive predictive values. As a result, pre- and posttest counseling are not always straightforward and may require discussions with multiple specialists including genetic counselors, obstetricians, and pediatricians/neonatologists. The purpose of this review is to summarize the screening options currently available to pregnant women to determine their risk of having a child affected by a chromosomal disorder. Screening for chromosomal abnormalities using ultrasonography, maternal serum analytes, cell-free DNA, and preimplantation genetic testing will be discussed here. Advances in the field, including the possible future use of cell-based noninvasive prenatal screening (NIPS) as a more accurate method for genetic screening and the incorporation of screening for copy number variants (microdeletions and duplications) into traditional cell-free NIPS will also be reviewed.

Attitude changes toward prenatal testing among women with twin pregnancies after the introduction of noninvasive prenatal testing: A single-center study in Japan

Aim

This study aimed to evaluate changes in prenatal testing among women with twin pregnancies before and after the introduction of noninvasive prenatal testing (NIPT). To date, no consensus on prenatal testing for twin pregnancies has been reached in Japan.

Methods

Women pregnant with twins who requested prenatal testing at Kyushu Medical Center from 2005 to 2018 were included in this study. Genetic counseling was provided to all participants. Their chosen methods of testing were collected and classified as invasive diagnosis (ID), noninvasive screening (NIS), and no test requested (NR). Parity, chorionicity, and methods of conception were assessed as attributes. The study period was divided into three terms according to testing availability in our center.

Results

After NIPT was introduced in our center, the use of ID methods decreased and eventually disappeared while NIS came to the forefront. NR was also the preferred choice of women with twin pregnancies before the introduction of NIPT and decreased but did not disappear after introducing NIPT. Women with twin pregnancies who underwent assisted reproduction initially showed hesitation to undergo testing but showed a strong preference for NIS after the introduction of NIPT. Differences in choice according to parity, chorionicity, and methods of conception were found before the introduction of NIPT but disappeared after introducing NIPT.

Conclusion

Increasing information about NIPT has apparently influenced the attitudes of women with twin pregnancies to prenatal testing in Japan. In particular, those who conceive through assisted reproductive technologies exhibited a strong preference for NIPT.

Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies: ACOG Practice Bulletin, Number 231

The incidence of multifetal gestations in the United States has increased dramatically over the past several decades. For example, the rate of twin births increased 76% between 1980 and 2009, from 18.9 to 33.3 per 1,000 births (1). However, after more than three decades of increases, the twin birth rate declined 4% during 2014-2018 to 32.6 twins per 1,000 total births in 2018 (2). The rate of triplet and higher-order multifetal gestations increased more than 400% during the 1980s and 1990s, peaking at 193.5 per 100,000 births in 1998, followed by a modest decrease to 153.4 per 100,000 births by 2009 (3). The triplet and higher-order multiple birth rate was 93.0 per 100,000 births for 2018, an 8% decline from 2017 (101.6) and a 52% decline from the 1998 peak (193.5) (4). The long-term changes in the incidence of multifetal gestations has been attributed to two main factors: 1) a shift toward an older maternal age at conception, when multifetal gestations are more likely to occur naturally, and 2) an increased use of assisted reproductive technology (ART), which is more likely to result in a multifetal gestation (5). A number of perinatal complications are increased with multiple gestations, including fetal anomalies, preeclampsia, and gestational diabetes. One of the most consequential complications encountered with multifetal gestations is preterm birth and the resultant infant morbidity and mortality. Although multiple interventions have been evaluated in the hope of prolonging these gestations and improving outcomes, none has had a substantial effect. The purpose of this document is to review the issues and complications associated with twin, triplet, and higher-order multifetal gestations and present an evidence-based approach to management.

Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226

Prenatal testing for chromosomal abnormalities is designed to provide an accurate assessment of a patient's risk of carrying a fetus with a chromosomal disorder. A wide variety of prenatal screening and diagnostic tests are available; each offers varying levels of information and performance, and each has relative advantages and limitations. When considering screening test characteristics, no one test is superior in all circumstances, which results in the need for nuanced, patient-centered counseling from the obstetric care professional and complex decision making by the patient. Each patient should be counseled in each pregnancy about options for testing for fetal chromosomal abnormalities. It is important that obstetric care professionals be prepared to discuss not only the risk of fetal chromosomal abnormalities but also the relative benefits and limitations of the available screening and diagnostic tests. Testing for chromosomal abnormalities should be an informed patient choice based on provision of adequate and accurate information, the patient's clinical context, accessible health care resources, values, interests, and goals. All patients should be offered both screening and diagnostic tests, and all patients have the right to accept or decline testing after counseling.The purpose of this Practice Bulletin is to provide current information regarding the available screening test options available for fetal chromosomal abnormalities and to review their benefits, performance characteristics, and limitations. For information regarding prenatal diagnostic testing for genetic disorders, refer to Practice Bulletin No. 162, Prenatal Diagnostic Testing for Genetic Disorders. For additional information regarding counseling about genetic testing and communicating test results, refer to Committee Opinion No. 693, Counseling About Genetic Testing and Communication of Genetic Test Results. For information regarding carrier screening for genetic conditions, refer to Committee Opinion No. 690, Carrier Screening in the Age of Genomic Medicine and Committee Opinion No. 691, Carrier Screening for Genetic Conditions. This Practice Bulletin has been revised to further clarify methods of screening for fetal chromosomal abnormalities, including expanded information regarding the use of cell-free DNA in all patients regardless of maternal age or baseline risk, and to add guidance related to patient counseling.

Screening for fetal aneuploidy

Screening is currently recommended in pregnancy for a number of genetic disorders, chromosomal aneuploidy, and structural birth defects in the fetus regardless of maternal age or family history. There is an overwhelming array of sonographic and maternal serum-based options available for carrying out aneuploidy risk assessment in the first and/or second trimester. As with any screening test, the patient should be made aware that a "negative" test or "normal" ultrasound does not guarantee a healthy baby and a "positive" test does not mean the fetus has the condition. The woman should have both pre- and post-test counseling to discuss the benefits, limitations, and options for additional testing. Rapid advancements of genetic technologies have made it possible to screen for the common aneuploidies traditionally associated with advanced maternal age with improved levels of accuracy beyond serum and ultrasound based testing. Prenatal screening for fetal genetic disorders with cell-free DNA has transformed prenatal care with yet unanswered questions related to the financial, ethical, and appropriate application in the provision of prenatal risk assessment.

First-trimester Ultrasound and Aneuploidy Screening in Multifetal Pregnancies

First-trimester ultrasound provides valuable information to help optimize the management of multifetal pregnancies. First trimester ultrasound the use of ultrasound and screening for aneuploidy has been well studied in singleton pregnancies. While evidence supporting the use of ultrasound in multiple gestations is well established, aneuploidy screening continues to evolve and its role in the prenatal setting has been less well studied. We review the importance of early first trimester ultrasound in assessing gestational age and chorionicity and early identification of anomalies, and review the various methods and limitations of aneuploidy screening and invasive diagnostic procedures in multiples.

Prenatal screening and diagnosis of aneuploidy in multiple pregnancies

Prenatal screening for aneuploidy has changed significantly over the last 30 years, from being age-based to maternal serum and ultrasound based techniques. Multiple pregnancies present particular challenges with regards to screening as serum-based screening techniques are influenced by all feti while ultrasound-based techniques can be fetus specific. Tests currently available tend to not perform as well in multiple compared to singleton pregnancies. Considerations must be given to these variations when discussing and performing screening for aneuploidy in this situation. Prenatal invasive diagnosis techniques in multiple pregnancies bring their own challenges from a technical and counselling point of view, in particular with regards to sampling error, mapping and assignment of results and management of abnormal results. This review addresses these particular challenges and provides information to facilitate care.

Zygosity and Chorionicity in the Prognosis of Triplet Pregnancies: Contribution of Microsatellites

We assess the prognostic values of zygosity and chorionicity in triplet pregnancies (TP) with the assistance of microsatellites analysis. 53 consecutive TP whose prenatal care and delivery occurred in our maternity hospital were included in this prospective study. Zygosity of all sets of triplets (alive or stillbirth, after 22 weeks of gestation) was determined by PCR-amplified microsatellites markers analysis. Chorionicity was determined by placental analysis in our fetopathology referral department and validated by molecular analysis of zygosity. Placental conformations, obstetrical and neonatal outcomes of TP were studied according to their zygosity and chorionicity. Monozygotic and to a greater extent, dizygotic TP were associated with an increase in placental ischemic injuries, velamentous cord insertions, twin-twin transfusion syndromes, fetal anomalies, and perinatal mortality when compared with the trizygotic TP (p<0.05). Monochorionic and more significantly, dichorionic TP presented with the same increases as trichorionic TP (p<0.05). Thus chorionicity easily determined by ultrasound evaluation during the first trimester of the pregnancy must remain the main prognosis criterion in TP. Taking into account the rare indications of prenatal diagnosis of zygosity, it became apparent that chorionicity has a greater impact than zygosity when distinguishing high-risk groups of TP.

Risk of birth defects increased in multiple births

BACKGROUND

Previous studies inconsistently suggest that there may be an association between birth defects and multiple births.

METHODS

Data were obtained from Zhejiang Hospital-Based Birth Defects Surveillance System during 2007 to 2009. There was a total of 545,018 pregnancies, including 537,593 singleton pregnancies, and 7425 multiple pregnancies (14,606 twins and 366 triplets). Odds ratio (OR)and confidence interval (CI) for birth defects were calculated for the singletons and multiple births.

RESULTS

The rate of birth defects in multiple births was 444.16 per 10,000 births versus 266.97 per 10,000 births in singletons (OR, 1.69; 95% CI, 1.57-1.84). A significant risk of birth defects was observed in 9 of 23 categories in multiple births. Both the multiple births and singletons with birth defects exhibited a similar proportion of single malformation, male children, and the mother living in a city. The multiple births with birth defects were delivered earlier (t = 7.90, p < 0.001) at a lower birth weight (t = 17.53, p < 0.001) compared to singletons with birth defects. The proportion of an antenatal diagnosis was higher in singletons compared with multiple births (p < 0.001). The multiple births with birth defects had a higher proportion of live birth and early neonatal death (p < 0.001).

CONCLUSIONS

An increased risk of birth defects in multiple births compared with singletons was confirmed.