The Role of Ultrasound in Multiple Pregnancy

Genotyping of STR and DIP-STR Markers in Plasma Cell-Free DNA for Simple and Rapid Noninvasive Prenatal Diagnosis of Zygosity of Twin Pregnancies

Due to the high rate of complications, special medical care must be provided especially for monozygotic twin pregnancies, which are characterized as having 2.5 times higher mortality of fetuses. In recent years, examination of cell-free DNA (cfDNA) circulating in maternal plasma has become a useful noninvasive method of prenatal diagnosis. However, fetal DNA constitutes only 3-20% of plasma cfDNA during pregnancy. Short tandem repeats (STRs) are routinely used in forensic examination of DNA mixtures and are able to identify 5% minority components. Haplotypes of deletion/insertion polymorphisms and STRs (DIP-STRs) are able to detect even 0.1% minority components of DNA mixtures. Thus, STRs and DIP-STRs seem to be a perfect tool for detection of fetal alleles in DNA isolated from maternal plasma. Here, we present a novel noninvasive prenatal diagnosis technique of determination of pregnancy zygosity based on examination of feto-maternal microchimerism of plasma cfDNA with the use of STRs and DIP-STRs. Our preliminary results based on 22 STR loci showed 67% sensitivity, 100% specificity and 82% accuracy for prenatal detection of twin dizygosity. The corresponding values for seven DIP-STRs were 13%, 100% and 54%, respectively. Owing to assay performance, low DNA input requirements, low costs (below 10 USD per patient) and simplicity of analysis, genotyping of STR/DIP-STR markers in maternal plasma cfDNA may become a useful supplementary test for noninvasive prenatal diagnosis of twin zygosity in cases when chorionicity and zygosity cannot be reliably determined by ultrasound examination and prognostic value may be provided by a DNA test determining pregnancy zygosity.

Delayed second twin delivery: benefits and risks

BACKGROUND

An increasing number of reports describe the delayed second twin delivery for days, or weeks with good results in the majority of the cases, and different survival rate between centers, without reported randomized controlled trials (RCTs).

OBJECTIVES

This study was designed to evaluate the suggested management of the delayed second twin delivery in the Sabah Maternity Hospital regarding its outcome, possible risks, and benefits.

PATIENTS AND METHODS

Forty-seven twin pregnancies with preterm labor (PTL) of the first fetus between 20-30 weeks, and delayed delivery of the second twin were included in this study. Studied women signed informed consent about the possible risks of keeping the live fetus in the hostile intrauterine environment, and benefits of the prolonged gestation for the second twin. Throughout the conservative treatment of the second twin, the studied women were hospitalized with regular follow up for infections, consumptive coagulopathy parameters, and wellbeing of the second twin.

RESULTS

There was significant difference in the gestational age at delivery between the first and second twin (22.6 ± 3.4 versus 34.3 ± 2.5 weeks; respectively, p = .01). There was significant difference in the birth weight between the first and second twin (435 ± 91.2 versus 1472 ± 61.5 g; respectively, p = .004). The rate of the cesarean delivery was significantly high during delivery of the second twin compared with the first twin (23.4% (11/47) versus 0% (0/47); respectively, p = .0001) with high survival rate for the second twin (85.1% (40/47)) after the delayed second twin delivery.

CONCLUSIONS

The birth weight, the gestational age, and the survival rate of the studied second twin significantly increased after the suggested management of the delayed second twin delivery.