In vitro fertilization (IVF) is a treatment that involves several steps leading up to the recovery of eggs from a woman's ovaries followed by placement of each of these eggs into a Petri dish together with her partner's sperm. The joining of the egg and sperm (fertilization) occurs outside the body while the eggs and sperm are kept in an incubator. Successfully fertilized eggs (embryos) are placed back into the woman's uterus several days later.
The following procedures are performed in conjunction with an IVF cycle:
Intracytoplasmic Sperm Injection (ICSI)
Intracytoplasmic sperm injection (ICSI) is an additional manipulation of sperm and egg during an IVF procedure. This procedure is done to overcome severe male factor problems.
Blastocyst Transfer
A blastocyst is an advanced embryo comprised of a large number of cells arranged in a spherical shape with an opening forming in the center. The blastocyst stage of development occurs on the fifth or sixth day after fertilization. This developmental stage is important because it represents the embryo’s transition from maternal genetic control to embryonic genetic control. In other words, the initial development of the embryo depends on the genetic message brought by the egg, and only after cell division for five days does the full embryonic genetic message begin to influence the growth of the embryo.
The development of a blastocyst is dependent on the proper mix of nutrients. In natural conception, the early embryo grows in the fallopian tube until the blastocyst stage, nourished by the secretions in the tube. In IVF, the embryo is cultured in a laboratory, housed in a small drop of fluid in a dish inside a controlled-environment incubator. Embryologists have replicated the nutrients from the fallopian tube environment in order to be able to grow embryos in the IVF lab to the blastocyst stage.
In spite of the tremendous strides made in understanding the culture of growth of embryos to blastocysts, only a minority of embryos will progress in the IVF lab from the multicellular stage at Day 3 to the fully developed blastocyst on Day 5. This may be because only the strongest, healthiest embryos are destined to survive.
In addition to the natural selection process that prolonged embryo culture may exert on embryos, other factors about Day 5 embryo transfer suggest that it might be associated with an increased chance for pregnancy. The timing of the embryo transfer is more like natural conception when the embryo is placed in the uterus after five days of growth. This timing would be expected to improve the chance of embryo implantation and pregnancy.
However, attempts to culture embryos from Day 3 to Day 5 are not always successful, and embryologists cannot tell which embryos will survive the extended culture period. The IVF physician and the embryologist must work closely together to recommend the day to perform embryo transfer. One major advantage of transfer of Day 5 embryos should be the use of single embryo transfer and the reduction of multiple pregnancy rates. One pitfall of blastocyst transfer is that a slightly increased chance of identical twinning has been seen with the transfer of blastocysts compared to Day 3 embryos.
Assisted Hatching
During conception the human embryo must hatch or break out of its surrounding membrane (zona) in order for successful implantation to occur in the uterus. Normally, this takes place when the embryo is about five or six days old (blastocyst stage), but in some cases, pregnancy may not occur due to failure of the embryo to hatch. Although the events leading to implantation of a human embryo are not completely understood, one contributing factor of hatching failure is the thickening of the embryo membrane, which typically occurs in eggs produced by older women.
In the last 15 years, assisted hatching of human embryos has been studied and adapted to improve the implantation and pregnancy rates of in vitro fertilization (IVF). A number of controlled studies have shown a benefit to assisted hatching through higher pregnancy and implantation rates in some groups of patients, especially where the female partner is older than 35 or there have been prior failed IVF cycles.
Our Approach to Assisted Hatching
At RHS, we offer assisted hatching to patients over the age of 35 and to those who have had prior IVF cycle failures. Occasionally, the embryologist will also suggest assisted hatching when the embryo membrane is exceptionally thick.
Currently, no information exists to suggest that assisted hatching is associated with any long-term effects on children conceived as a result of IVF cycles where this procedure was used. Data from the national IVF registry at the Center for Disease Control (CDC) suggests that the chance of monozygotic (identical) twinning may increase with assisted hatching, however this risk is less than 1% of all pregnancies conceived through IVF. This is important because monozygotic twin pregnancies are at higher risk of complications than non-identical twins.
Sperm Cryopreservation
Sperm cryopreservation is a process that allows sperm cells to be frozen indefinitely for future use. Usually sperm is frozen in circumstances where the sperm have been surgically removed from the male partner. The sperm would then be used in an IVF cycle. Prior to freezing any sperm specimens, the male must have blood tests done to check for any viral infections.
Preimplantation Genetic Diagnosis
Preimplantation Genetic Diagnosis (PGD) identifies genetic anomalies in embryos before they are transferred to the uterus. PGD is performed as an addition to in vitro fertilization (IVF) and usually requires one or more cells of the developing embryo to be removed for analysis. Embryos identified as having a genetic anomaly are not transferred to the uterus, therefore avoiding miscarriage or birth of an unhealthy child before the pregnancy is established. Since PGD cannot evaluate every gene or chromosome, there is still a small chance that an unhealthy child can be born.
The two primary groups of candidates for PGD are patients with a known genetic predisposition to a specific disease (Cystic Fibrosis, Huntington's Disease, etc.) and patients with an elevated risk for producing children with aneuploidy (an abnormal number of chromosomes), usually females of advanced maternal age. RHS works with several world-renowned molecular genetics specialists and can assist patients with coordinating the best care for their specific genetic needs.
