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Comprehensive Chromosomal Analysis of IVF Embryos
Patients undergoing in vitro fertilization (IVF) with the Colorado Center for Reproductive Medicine screening technique called comprehensive chromosomal screening (CCS) have a clinical pregnancy success rate of 77 percent, according to statistics from a study being conducted at the Colorado fertility clinic. This compares extremely favorably to the worldwide IVF pregnancy success rate, which is approximately 30 percent.
Normally, an embryo has a total of 46 chromosomes – half from the mother and half from the father. However, sometimes an egg or sperm may have an abnormal number of chromosomes, which results in an embryo with aneuploidy. The majority of embryos with aneuploidy will not implant in the uterus or will result in a miscarriage. CCS is a type of preimplantation genetic screening (PGS) that screens all 23 chromosome pairs in a few cells removed from a Day 5 or 6 embryo (blastocyst). The CCRM study used microarray analysis and comparative genomic hybridization (CGH) as the testing method. The goal is to reduce the likelihood of implantation failure, miscarriage and pregnancies affected with chromosomal abnormalities by transferring only embryos that have the correct number of chromosomes. The embryos are frozen and transferred at a later date.
"Since a high proportion of failed pregnancies are due to abnormalities in chromosome numbers, CCS helps eliminate one variable from the equation," says William Schoolcraft, MD, Medical Director and Founder of CCRM.
A total of 114 patients in the CCRM study have had egg retrieval and subsequent frozen blastocyst transfer. Indications for the testing include advanced maternal age, previous IVF failure(s), and a history of multiple miscarriage(s). After the blastocyst embryos were biopsied, they were cryopreserved using a new technique called vitrification, which has resulted in a 97 percent blastocyst survival rate. The uterus is then prepared for a frozen embryo transfer after the woman's body is allowed to naturally rid itself of the ovarian stimulation drugs required during an IVF cycle. Eighty-eight of the 114 patients in the study (77percent) have ongoing clinical pregnancies, including 41 healthy deliveries to date. The first baby conceived with this procedure was born in June 2008.
"We are thrilled with the outcome of our CCS clinical study," says Dr. Schoolcraft. "I am also impressed with the ability of thawed embryos to do so well after transfer in cycles unaffected by fertility drugs. With these promising early results, we are continuing the clinical trial, giving patients access to comprehensive chromosome analysis of their embryos with an increased likelihood of pregnancy."