CVS

Chronic villus sampling (CVS) is another procedure that can be used to detect genetic disorders in a fetus. This can be done in place of amniocentesis. Like amniocentesis, it tests for chromosomal abnormalities in your baby. Unlike amniocentesis, it cannot test for other abnormalities such as neural tube defects.

A perinatologist usually performs CVS in the first trimester, around 10 to 12 week gestation. Prior to the procedure, an ultrasound is done to confirm gestational age and fetal viability (a live baby), as well as to check the location of the placenta. The procedure involves inserting a thin plastic catheter with a metal insert through your cervix or through the abdomen into the placenta, after the area has been cleaned with an antiseptic iodine solution. If the procedure is done through the cervix, a speculum is placed in the vagina (similar to performing a Pap smear) to expose the cervix. Small fragments of the placental tissue are then obtained through the catheter via suctioning from an attached syringe. The catheter is then removed, and the tissue fragments are isolated and sent to the cytogenetics laboratory. The entire procedure is done under continuous ultrasound monitoring to help guide the catheter correctly.

Complications of CVS include, but not limited to: hemorrhage, uterine perforation, rupture of the amniotic membranes, premature labor, and miscarriage. In addition, the possibility that the procedure could produce a birth defect cannot be totally excluded, although this risk appears to be very negligible. In experienced hands, the rate of complications with CVS and amniocentesis are equal.

The main advantage of CVS over amniocentesis is the fact that it is done early in pregnancy and therefore, if termination of pregnancy is desired for an abnormal finding, it is much safer than if done in the mid second trimester.

The main disadvantage of CVS is that it cannot check for neural tube or abdominal wall defects. Therefore, a maternal serum AFP (alpha-fetal protein) screening and/or a Level II ultrasound are recommended in the second trimester