Primary Prenatal Care: Screening, Prevention, and Treatment of Viral Infections.

Prenatal care providers are responsible for a basic understanding of the viral contagions that place women and fetal well-being at risk during pregnancy. This article reviews the evidence-based routine prenatal screening guidelines for previously unrecognized maternal infection, counseling toward risk reduction, recommended maternal immunizations, and the management of maternal and fetal complications of some viral exposures and infections.

Selective termination procedures in monochorionic pregnancies.

Monochorionic twins have placental anastomoses that to varying degrees create a common circulation. This presents unique challenges for the performance of selective fetal termination in cases of twin-twin transfusion syndrome, twin reversed arterial perfusion sequence, or discordant twin abnormalities. Multiple methods of interrupting the affected twin's circulation have been attempted with variable success. One of the most frequent complications of any approach is iatrogenic preterm premature rupture of membranes. Laser coagulation in the midtrimester appears to be safe and effective; however, it is only available at limited centers. Currently, bipolar coagulation is the method of choice in the second half of pregnancy. The recently reported technique of radiofrequency ablation appears to be successful with minimal complications. Exploration of further percutaneous and noninvasive techniques, as well as interventions to decrease the morbidity arising from preterm membrane rupture, may lead to increased survival of the remaining twin and reduced risk of maternal complications.

Genomic surveys by methylation-sensitive SNP analysis identify sequence-dependent allele-specific DNA methylation.

Allele-specific DNA methylation (ASM) is a hallmark of imprinted genes, but ASM in the larger nonimprinted fraction of the genome is less well characterized. Using methylation-sensitive SNP analysis (MSNP), we surveyed the human genome at 50K and 250K resolution, identifying ASM as recurrent genotype call conversions from heterozygosity to homozygosity when genomic DNAs were predigested with the methylation-sensitive restriction enzyme HpaII. Using independent assays, we confirmed ASM at 16 SNP-tagged loci distributed across various chromosomes. At 12 of these loci (75%), the ASM tracked strongly with the sequence of adjacent SNPs. Further analysis showed allele-specific mRNA expression at two loci from this methylation-based screen--the vanin and CYP2A6-CYP2A7 gene clusters--both implicated in traits of medical importance. This recurrent phenomenon of sequence-dependent ASM has practical implications for mapping and interpreting associations of noncoding SNPs and haplotypes with human phenotypes.