Special Needs During Pregnancy
Depending on a mother's risk profile ,special tests may be ordered to detect fetal defects.
Ultrasound utilizes sound waves that bounce off tissues. These waves of sound are deflected and converted into images of the fetus, which then appear on a screen. Ultrasound detects the number of fetuses, age and growth rate of the fetus, location of the placenta, fetal position and heart rate, amount of amniotic fluid in the uterus and some birth defects.
Alpha-fetoprotein screening is a blood test used to detect neural tube defects or Down syndrome. It is performed between weeks 15-18. Every fetus produces alpha-fetoprotein that passes from the amniotic fluid into the mother's blood. If a fetus has an open neural tube defect (spina bifida or anancephaly), excessive quantities of alpha-fetoprotein leak into the mother's blood. Low levels of alpha-fetoprotein are associated with Down syndrome. This test identifies 90 percent of open neural tube defects and 25 percent of Down's cases. False positives occur almost 5 percent of the time.
Fetal cells present in the amniotic fluid are collected from a needle inserted into the abdomen. These cells are then cultured and grown in order to detect chromosomal abnormalities, including Down syndrome. The test is performed between 14 - 18 weeks.
Chorionic villi are microscopic projections that compose the placenta. They have the same genetic constitution as the fetus. The villi sample is collected either through a needle in the abdomen or through a vaginal catheter and cultured to detect chromosomal abnormalities. This test is performed in the first trimester.
