Moving toward an IVF cycle can be both a nervous and exciting time. There are multiple ultrasounds and recurrent blood work. It is not uncommon to feel like a pin cushion – and partially expected. Frequent ultrasounds document the progress of growing follicles. Images that were difficult to assess by patients, become quite pronounced as women become more familiar with the morning’s regimens. Much time is spent guesstimating how many follicles will translate into how many eggs and how many of these eggs would be mature and how many would fertilize. The egg retrieval turns the guessing into reality. But what happens after the egg retrieval?
On the day of the retrieval, we know how many oocytes (eggs) are retrieved. If ICSI is ordered, the oocytes are stripped of their protective cumulus covering and then injected (and we know about maturity then); and if standard insemination is the course, sperm droplets are placed upon the eggs without the cumulus being removed (as it aides in the fertilization process). The next morning, the labs assess how many eggs have fertilized; the fertilized egg is now an embryo. These embryos are then housed in special incubators. The environment supporting their growth mimics the uterine environment. And there, we expect them to progress, undisturbed and bathed in rich growth media.
On the morning of the transfer, the embryos are removed from the incubators and graded according to their morphology (how they look). We use their stage of maturity (how close they are to being a blastocyst) and rate the characteristics of cells composing the embryo to predict which embryo has the highest chance of pregnancy. Realize, we use these growth characteristics as a surrogate for whom we believe to be the best embryo for transfer on that day. Depending upon the cohort of embryos and specifics to each couple’s history, we can predict reasonably, the chances of pregnancy.
On the transfer day, selected embryos are transferred from the confines of the incubator to the confines of the best incubator, the uterus. Ultrasound again is used to guide the transfer catheter into the uterine cavity. The embryo(s) released, percolate for 12-24 hours awaiting the final endometrial maturation. Then, hopefully, the embryo(s) burrow into the lining and the placenta begins its task of establishing and maintaining pregnancy. The progesterone support helps to maintain the pregnancy until the placenta has the strength to maintain pregnancy throughout gestation (at about 8-9 weeks).
Remaining embryos that are candidates for transfer (and making a baby) are then cryopreserved. Essentially, they are in suspended animation with all cellular processes coming to a seeming halt. They can be thawed at a later time and transferred, affording a pregnancy rate comparable to the rates accomplished when they were created.