The quad screen is usually done between 15 and 18 weeks of pregnancy, but it can be done as late as 20 weeks and 6 days. You'll have a blood sample taken and sent to a lab for analysis. Results are usually available in about a week.
The test measures the levels of four substances in your blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and the hormone inhibin A.
High AFP can mean several things. A baby produces AFP throughout gestation, and a certain amount of it should cross the placenta into the mother's bloodstream at each stage.
If there's more AFP than expected, it may mean that you're carrying more than one baby or that your baby is older than your practitioner thought. But in some cases, it's a sign of an abnormal opening in the baby's spine (spina bifida), head, or abdominal wall that's allowing AFP to leak out. In rare cases, it can also signify a problem with the baby's kidneys. And in some cases, it doesn't mean any of those things.
Low AFP, low estriol, high hCG, and high inhibin A are associated with a higher risk for Down syndrome. Low levels of the first three means your baby has a higher than normal risk of having trisomy 18, a more severe and less common chromosomal abnormality.
Certain results may also indicate that you are at a somewhat greater risk for problems such preeclampsia, premature birth, intrauterine growth restriction, or miscarriage. Knowing this can enable you and your practitioner to be on the lookout for signs of trouble.
To determine your baby's chances of having Down syndrome or trisomy 18, your levels of the four substances are plugged into a formula along with your baby's gestational age and your age.
Your age is factored in because although anyone can have a baby with a chromosomal abnormality, the risk increases as you age. For example, your likelihood of carrying a baby with Down syndrome ranges from about 1 in 1040 at age 25 to about 1 in 75 at age 40.
To determine your baby's chances of having a neural tube defect, your level of AFP is plugged into a formula along with your age, your baby's gestational age, and other factors.
If you're having the quad screen as part of an integrated or sequential screening, the results will be combined with those from the tests you took in your first trimester for a more comprehensive risk assessment and a higher detection rate.