Identification of fetal abnormalities through cordocentesis is typically performed for pregnancies older than how many weeks?

Cordocentesis, also known as percutaneous umbilical blood sampling (PUBS), is a procedure used to obtain a sample of fetal blood from the umbilical cord. This technique is most commonly performed after 18 weeks of gestation. The reason for this timing is largely due to the development of the fetal structures and the accessibility of the umbilical cord, which becomes easier to visualize and access after this gestational age.

Prior to 18 weeks, the risk of complications for both the mother and the fetus is higher, and the technical challenges associated with locating and sampling from the umbilical cord increase. As gestation progresses beyond 18 weeks, the procedure becomes safer and more reliable, allowing for more accurate diagnoses of fetal conditions such as genetic disorders, blood group incompatibilities, and infections.

In summary, the cut-off point of 18 weeks ensures that the procedure is performed at a stage when the benefits can be maximized while minimizing risks to both the fetus and the mother, making it the correct answer.