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Prenatal diagnosis employs a variety of techniques to determine the health and condition of an unborn fetus. Without knowledge gained by prenatal diagnosis, there could be an untoward outcome for the fetus or the mother or both. Congenital anomalies account for 20 to 25% of perinatal deaths. Specifically, prenatal diagnosis is helpful for
• Managing the remaining weeks of the pregnancy
• Determining the outcome of the pregnancy
• Planning for possible complications with the birth process
• Planning for problems that may occur in the newborn infant
• Deciding whether to continue the pregnancy
• Finding conditions that may affect future pregnancies
There are a variety of non-invasive and invasive techniques available for prenatal diagnosis. Each of them can be applied only during specific time periods during the pregnancy for greatest utility. The techniques employed for prenatal diagnosis include

• Ultrasonography
• Amniocentesis
•Chorionic villus sampling
• Fetal blood cells in maternal blood
• Maternal serum alpha-fetoprotein
• Maternal serum beta-HCG
• Maternal serum estriol
Ultrasonography
This is a non-invasive procedure that is harmless to both the fetus and the mother. High frequency sound waves are utilized to produce visible images from the pattern of the echos made by different tissues and organs, including the baby in the amniotic cavity. The developing embryo can first be visualized at about 6 weeks gestation. Recognition of the major internal organs and extremities to determine if any are abnormal can best be accomplished between 16 to 20 weeks gestation.
Although an ultrasound examination can be quite useful to determine the size and position of the fetus, the size and position of the placenta, the amount of amniotic fluid, and the appearance of fetal anatomy, there are limitations to this procedure. Subtle abnormalities may not be detected until later in pregnancy, or may not be detected at all. A good example of this is Down syndrome (trisomy