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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Twins: Antepartum assessment and Intrapartum management
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4 Twin Pregnancy: Double Trouble?
Step 4. Fetal Abnormalities: Serum Screening
FETAL ABNORMALITIES
Since there are two fetuses, the chance of a fetal anomaly or aneuploidy is also increased in twin pregnancy. The age risk for fetal Down syndrome begins at an earlier age in women with twins. (Matias) A 33 year old woman has the same 1 in 270 risk of Down syndrome as does a 35 year old with a singleton pregnancy, and this should be taken into account when deciding for whom “advanced maternal age” counseling is appropriate. (Bush) Both first trimester “combined screening” with nuchal translucency measurement and free beta HCG and PAPP-A levels at 11-13 weeks, as well as second trimester screening with “the quad test” at 15-21 weeks (see the Perinatologist’s Corner module on Prenatal Genetic Screening – Serum and Ultrasound), may be reliably offered to women with twins. The lab will enter the fact that this is a twin pregnancy into the computer-generated risk assessment, and the values reported will be corrected for twins.
When screening for neural tube defects with maternal serum alpha fetoprotein, the twin cut-off is 3.5 multiples of the median, not 2.5 MoM. Remember that the risk reported will be for the pregnancy; it cannot say which twin may be affected. A thorough sonographic anatomic survey at 18 weeks however should be able to demonstrate if one of the twins has an anomaly. Interestingly, monochorionic twins may be at a greater risk for abnormalities, and may be discordant for anomalies, as they are not all monozygotic.
