Invasive Genetic Diagnosis in Multiple Pregnancies

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.

Why are monozygotic twins different?

Although popularly designated as "identical", monozygotic (MZ) twins are rarely identical. Much has been speculated on the origin of MZ twins and several theories have been proposed. Post-fertilization events, such as chromosomal mosaicism, skewed X-inactivation and imprinting mechanisms, as well as other epigenetic mechanisms are responsible for the differences between MZ twins. Numerous discordant MZ twins have been reported including discordance for lateral asymmetry, major malformation, growth and intrauterine death of the co-twin. This discrepancy may have long-term implications on complex diseases and their predisposition, organ transplantation and interpretation of twin-based studies. We reviewed the genotypic and phenotypic differences between MZ twins and discuss their main causes.

Mild ovarian stimulation

PURPOSE

To evaluate the efficacy of using only mild ovarian stimulation protocols for in vitro fertilization. Both groups with decreased and normal ovarian reserve were evaluated.

METHODS

Three different mild stimulation protocols were evaluated: natural with no exogenous follicle stimulation hormone (FSH) drugs at all, natural with a boost of low dose FSH to complete follicular maturation, and minimal stimulation with low dose (75-150IU) FSH from day 3-5 of the menstrual cycle. Ethinyl estradiol was sometimes used to lower high day 3 serum FSH.

RESULTS

Good pregnancy and implantation rates were found even in those women with elevated serum FSH that could only generate one follicle.

CONCLUSIONS

Mild ovarian stimulation seems preferable to high dose FSH regimens in women with elevated day 3 serum FSH based on previous poor reported pregnancy rates with the latter protocols. Comparable pregnancy rates to high dose regimen were seen in women with normal egg reserve at much lower risk and cost.

Litigation in multiple pregnancy and birth

Multiple birth rates have increased in most developed countries. The potential of a medical legal dispute increases when complications are common. Failure to perform the basic and standard care follow-up often misses the complication and the chance of a timely referral to a center experienced in the diagnosis and management of these complexities of a multiple pregnancy. In this article, several examples are discussed in which departure from the standard of care of multiple pregnancies were the basis of the allegation.

Cordocentesis in multifetal pregnancies

OBJECTIVE

To describe the experiences in diagnostic cordocentesis in twin pregnancies at midpregnancy

METHODS

The database and medical records of pregnant women attending Maternal Fetal Medicine Unit of the hospital for diagnostic cordocentesis at midpregnancy between January 1989 and September 2006 were retrospectively reviewed.

RESULTS

During 17 years of experience, 4,241 cordocenteses at midpregnancy were performed for prenatal diagnosis, including 59 procedures in 30 multiple pregnancies (29 twins and 1 triplet). The mean gestational age at the time of cordocentesis was 19.5 +/- 1.6 weeks. Success rate of the samplings was 98.3% with one sample was maternal blood contamination. Averaged-time used of the procedures was 8.2 minutes (range 1-45 minutes). The procedure-related complications included transient bleeding at puncture site (8.5%) and transient fetal bradycardia (22.0%). The total fetal loss rate was 10.5% but there was no cordocentesis-related fetal loss (0.0%), defined as a fetal loss within 2 weeks after the procedure.

CONCLUSION

This study may provide a new insight on the safety of cordocentesis in multifetal pregnancies at midpregnancy. The procedure-related fetal loss is not as high as reported in the past. This study suggests cordocentesis be a relatively safe and highly successful in obtaining fetal blood samples.

Twin gestation pregnancies: genetic counseling and testing experience

We report on the prenatal genetic counseling and testing experience in 343 pregnancies with twin or higher multiple gestations. By self-report, 8% (27/343) parents of these pregnancies reported meeting with a genetic counselor, and 23% (79/343) elected prenatal genetic testing. The most common testing procedures elected were maternal serum analyte screening and amniocentesis to identify fetuses with aneuploidy or neural tube defects. Use of prenatal genetic testing was correlated with advanced maternal age. No association was found between use of genetic testing and use of OI/ART or the length of time needed to conceive. Forty percent (11/27) of those who met with a genetic counselor opted to decline prenatal testing/screening. These data suggest that although clients with multiple gestation pregnancies would likely benefit from genetic counseling, many are not availing themselves of this service. Implications of these data for the genetic counseling profession are discussed.

Prenatal diagnosis and multiple pregnancy

The incidence of twins, triplets, and high-order multiples has increased dramatically in the last two decades secondary to greater reliance on fertility treatments and to delayed childbearing. Offspring of a multiple gestation are at increased risk for both chromosomal and structural abnormalities. Prenatal diagnosis in these patients is challenging. Options for screening tests are limited. Invasive diagnostic procedures are complex. Likewise, physicians and patients may be faced with the dilemma of deciding how to manage discordant results. The following paper will review the unique concerns associated with prenatal diagnosis in a multiple pregnancy and the current methods of prenatal screening in these patients. Invasive prenatal diagnosis will also be explored.