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How Accurate Is AFP Testing for Twins?



High AFP results may be helpful in detecting twin pregnancies, but not necessarily accurate in detecting abnormalities in twin fetuses.

More Info: AFP (alpha-fetoprotein) is produced by the developing fetus and ends up in the mother’s bloodstream. The screening is performed by simply obtaining a blood sample from the mother’s arm. Screening for AFP levels is usually done at the beginning of the second trimester, between your 15th and 17th week of pregnancy, due to the fact that a dramatic increase in AFP occurs between the 4th and 6th month of pregnancy. An elevated AFP level may be indicative of one of three things:

  1. The mother is farther along in pregnancy than she thought. A follow-up ultrasound may confirm fetal gestational age.
  2. The baby is at risk for certain birth defects such as neural tube defects (spina bifida), abdominal wall defects, or physical/mental defects such as Down’s Syndrome. An ultrasound and/or amniocentesis may be used to confirm or rule-out defects.
  3. The mother is carrying twins. Each baby produces alpha-fetoprotein, therefore producing an abnormal AFP result (false positive). An ultrasound can be used to confirm a twin pregnancy. A re- calculated AFP may be done using a normal-for-twins range of results.

Therefore, AFP screening is just that, a screening. It is not a definitive diagnostic tool. The screening can only tell you if your baby may or may not be at risk for certain birth defects. Again, a follow-up ultrasound and/or amniocentesis may be performed to rule-out or confirm fetal abnormalities and twin pregnancies



“Alpha fetoprotein: MedlinePlus Medical Encyclopedia.” National Library of Medicine – National Institutes of Health. N.p., n.d. Web. 21 Apr. 2010.

O’Neil, Dr. Dennis. “Detection.” HUMAN CHROMOSOMAL ABNORMALITIES. Behavioral Sciences Department, Palomar College, San Marcos, California, n.d. Web. 21 Apr. 2010. <>.

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