Perhaps one of the most important application of fetal DNA in maternal plasma is the non-invasive genotyping of the fetus in pregnancies complicated by red cell alloim-munisation. Non-invasive fetal Rh-D genotyping was first reported in 1998  and since 2001, the International Blood Group Reference Laboratory (IBGRL) in Bristol has offered fetal Rh-D typing using cell free fetal DNA in maternal plasma, to obstetricians caring for alloimmu-nised women. This has significantly reduced the number of invasive procedures carried out in the UK for fetal Rh-D genotyping . More recently, the IBGRL has also started offering fetal Rh-c and Kell genotyping using the same technique.
Other genetic disorders such as myotonic dystrophy , achondroplasia  and cystic fibrosis  have all been diagnosed using fetal DNA in maternal plasma. In addition, Hong Kong investigators , using fetal DNA to exclude or confirm the presence of the paternally inherited mutant allele in beta-thalassaemia major, have been able to identify at-risk fetuses who then need invasive testing.
A major limitation of using DNA in maternal blood is the fact that the mother and fetus share, on average, half of their genomic DNA sequences. Thus, it is only possible to detect uniquely fetal DNA sequences that are paternally inherited. Novel approaches, such as using gender-independent polymorphisms, epigenetic markers, or circulating mRNA sequences, will eventually allow this technology to be applied to female fetuses. Comparative genome hybridization and microchip assays may make it possible that amplified fetal nucleic acids will ultimately permit a non-invasive fetal genome scan as part of routine prenatal screening.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.