The four substances measured in the blood to detect these conditions are alpha-fetoprotein (AFP), a protein secreted by the fetal liver; an estrogen called estriol; human chorionic gonadotropin (HCG); and a substance known as inhibin, a protein secreted by the ovary. Data on your age, your last menstrual period, your race and your diabetic status will be collected and figured into a mathematical equation that yields an estimate of risk. A positive screen does not provide a diagnosis but indicates that further evaluation should be considered. Measurement of the markers in the quad screen is tied to weeks of gestational age, so this must be determined with great accuracy. Indeed, the most common reason for an abnormal level is inaccurate dating. Maternal accuracy in reporting the first day of the last menstrual period, ultrasound dating and assessment of uterine size are used to establish the age of the embryo.
More research is being conducted to find other conditions that can be predicted through serum-marker testing. It's possible that this testing may someday be able to predict preterm labor and preeclampsia.
With the improvement of ultrasound and biochemical tests such as the quad screen, amniocentesis is no longer the standard of care for all women at or above age 35. These moms, however, should still be carefully counseled about the risks and all of the tests available to them. Pregnancy-induced hypertension, placental dysfunction, diabetes, renal disease, and risk of cesarean and postpartum hemorrhage and lengthier recovery are some of the risks that come with advanced maternal age. Miscarriage and stillbirth occur with greater frequency, and, with the exception of neural tube defects, fetal malformations are more frequent.