Normal Ranges for Double Marker Test in Pregnancy

Alpha-Fetoprotein (AFP) Normal Ranges

The American College of Medical Genetics recommends that AFP levels normally increase by approximately 10-15% per week during the second trimester 3
For singleton pregnancies, normal AFP levels are below 2.0-2.5 multiples of the median (MoM) 4
The optimal time for AFP screening is between 16-18 weeks gestation, as recommended by the American College of Medical Genetics 1, 5
AFP levels can be affected by maternal weight, race, presence of insulin-dependent diabetes, number of fetuses, and family history of neural tube defects, according to the American College of Medical Genetics 1

In Down syndrome cases, hCG levels are often elevated (higher than normal), as reported by the American College of Medical Genetics 1, 2
In trisomy 18 cases, hCG levels are typically low, according to the American College of Medical Genetics 1
Like AFP, hCG levels should be interpreted based on gestational age, with testing optimally performed between 16-18 weeks, as recommended by the American College of Medical Genetics 5

AFP values above 2.0-2.5 MoM may indicate neural tube defects, ventral wall defects, or other complications, according to the American College of Medical Genetics 1
Elevated hCG (>2.0-2.5 MoM) may be associated with increased risk of Down syndrome, preeclampsia, and preterm labor, as reported by the American College of Medical Genetics 1
Results must be interpreted in the context of gestational age, with reinterpretation needed if gestational age changes by 2 or more weeks after ultrasound dating, as recommended by the American College of Medical Genetics 1, 6
Ultrasound dating of pregnancy improves accuracy of screening by reducing false-positive rates, according to the American College of Medical Genetics 1

Results are reported as multiples of the median (MoM), which adjusts for gestational age, as recommended by the American College of Medical Genetics 3
Each laboratory should establish its own normative data rather than relying solely on package inserts, according to the American College of Medical Genetics 3
Screening performance is improved by expressing gestational age as weeks and days or decimal weeks rather than completed or rounded weeks, as reported by the American College of Medical Genetics 3
Maternal weight adjustment is important as AFP levels are inversely related to maternal weight, according to the American College of Medical Genetics 4
The double marker test is part of screening and not diagnostic; abnormal results require follow-up with genetic counseling, targeted ultrasound, and possibly amniocentesis, as recommended by the American College of Medical Genetics 1, 5

Failing to adjust for gestational age when interpreting results, as warned by the American College of Medical Genetics 3
Not considering maternal factors that can affect marker levels (weight, race, diabetes), according to the American College of Medical Genetics 1
Using the same cut-off values for twin pregnancies as for singleton pregnancies, as cautioned by the American College of Medical Genetics 4
Not reinterpreting results when gestational age is revised by ultrasound, as recommended by the American College of Medical Genetics 1, 6