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Genetic Services

Second Trimester Screening

Available in the 15th through 20th weeks of pregnancy

For many years the established standard of care for women under 35 has been to offer second trimester screening. This screening is performed in your OB’s office and has multiple names including: maternal serum screening, triple screen, quadruple screen, or alpha fetoprotein (AFP) test. This blood test is usually performed between the 15th and 20th week of pregnancy. 

Second trimester screening measures three or four different pregnancy hormones: AFP, human chorionic gonadotropin (hCG),  unconjugated estriol (uE3),  and inhibin (DIA) produced by the pregnancy. The levels of the hormones are collectively compared to estimate risks for three conditions:  open neural tube defect (spina bifida), Down syndrome (Trisomy 21), and Trisomy 18.  The results also incorporate maternal age, recognizing the chance for Down syndrome and Trisomy 18 increases with advancing maternal age.

A positive, or abnormal, screening result does not mean that your pregnancy has a genetic problem. Abnormal screening results only indicate that the pregnancy is at increased risk for an abnormality and that additional, more definitive, fetal testing such as amniocentesis should be considered. A negative, or normal, screening result indicates the pregnancy is at a low risk for these abnormalities. Second trimester screening alone cannot   rule out any of these conditions. Therefore it is important not to make decisions about a pregnancy based only on the blood test.

Many women are considering the first trimester screen (FTS) instead of the maternal serum screen. The FTS has a higher detection rate, examines for an additional severe chromosome defect called Trisomy 13, and is performed earlier in pregnancy.  However, the FTS does not screen for open neural tube defects, so a detailed ultrasound or AFP only measurement is recommended in the second trimester.

To schedule an appointment, click here or call 800.552.4363 or 703.698.7355.