Chapter 26: FETAL BLOOD SAMPLING

INTRODUCTION

Fetal blood sampling was performed for the first time more than 30 years ago under fetoscopic visualization.¹ In the early 1980s, cordocentesis under ultrasound guidance,² also referred to as "percutaneous umbilical blood sampling" (PUBS), was introduced, bringing forth a new era in fetal assessment and therapy. Fetal blood obtained by PUBS was the optimal specimen to directly measure fetal hematologic, metabolic, and endocrine parameters; to conduct genetic testing (including chromosomal and single-gene studies); to determine whether or not there was fetal hypoxemia and/or acidemia; as well as in the diagnosis and follow-up of suspected congenital infections.^{3,4, and 5}

In recent years, progress in molecular genetics as well as the advances in noninvasive techniques of antenatal surveillance, have largely obviated the need for PUBS. For instance, rapid analytical techniques, such as fluorescent in situ hybridization (FISH), and quantitative fluorescent polymerase chain reaction (qf-PCR), enable the examination of chromosomes within a few hours, without the need to access the fetal circulation.^{6,7,8,9, and 10} Finally, studies of free fetal DNA in maternal blood to define paternally inherited fetal genes, and noninvasive prenatal diagnosis of aneuploidy may further reduce the need for analysis that required PUBS in the past.¹¹ In pregnancies at risk for fetal infection, such as in the case of toxoplasmosis, cytomegalovirus (CMV), and varicella-zoster virus, amniotic fluid analysis with subsequent PCR amplification of bacterial/viral RNA/DNA has proven to be a valuable alternative diagnostic tool, carrying lower risks and with high positive and negative predictive values.^{12,13,14, and 15} One of the most common indications to perform PUBS, which is screening, identification, and follow-up of fetuses at risk for anemia, can be delayed or avoided by serial assessment with Doppler velocimetry of the peak systolic velocity in the fetal middle cerebral artery (MCA).¹⁶ Moreover, phenotypic diagnosis of inherited defects of hemostasis and primary immunodeficiency diseases have been superseded by first trimester molecular diagnosis in chorionic villi.^17–18 Over the last decade, attempts have been made to derive a risk-stratified approach to patient-specific therapy of alloimmune thrombocytopenia (AIT), while keeping invasive procedures for fetal platelet count to a minimum.¹⁹

In conclusion, even though less invasive or noninvasive techniques can now overcome the need for performing PUBS, direct access to the fetal circulation still remains crucial in selected cases, both for diagnostic and therapeutic purposes, including intrauterine platelet or red cell transfusion. The purpose of this chapter is to briefly review the techniques as well as the ...