To obtain fetal blood samples for fetal karyotyping

To aid in identifying hemophilia, hemoglobinopathies, fetal infections, chromosomal abnormalities, fetal distress, and fetal drug levels

To provide access to fetal circulation for transfusion in utero

To assess acid-base balance of fetuses with intrauterine growth restriction

Make sure the patient has signed an appropriate consent form.

Explain the purpose, benefits, and risks of the test.

Make sure that the patient is past her 16th week of gestation.

Tell the patient that a needle will be inserted into her abdomen.

Inform the patient that an ultrasound examination will be done to help guide the insertion of the needle.