Egg Freezing
Human oocyte cryopreservation or egg freezing is a process in which a woman’s eggs (oocytes) are extracted, frozen and stored for later use. The eggs are stored until she is ready to become pregnant, at which point the eggs can be thawed, inseminated and the resulting viable embryos transferred to the uterus in hopes of achieving a pregnancy.
The major reasons for women wishing to preserve their fertility include:
Social reasons: Women may opt to delay their childbearing for personal reasons (e.g. no partner, education etc.) and choose to freeze eggs to avoid the age-related decline in egg quality that naturally occurs.
Medical reasons: Women who are diagnosed with certain medical conditions such as cancer may choose to freeze eggs prior to undergoing treatments that can compromise egg quality
Religious/ Ethical reasons: As surplus eggs are often generated during ovarian stimulation, persons may opt to freeze surplus eggs versus surplus embryos to avoid potential concerns involving the discard of frozen embryos.
Family history: Some persons may be aware of a family history that may compromise fertility, such as premature menopause and opt to freeze their eggs in an attempt to avoid future fertility concerns.
The process involves undergoing hormonal stimulation to encourage the ovaries to produce several eggs. Once the eggs are of adequate maturity, the eggs are collected under sedation using a needle. Once collected, the cumulus cells surrounding the eggs are removed, maturity assessed and eggs immediately frozen using the technique called vitrification. The process generally takes 4-6 weeks depending on the protocol selected.
To date studies show that the ideal time to freeze eggs is early to mid-30’s. Here at HWFMU we have criteria to determine eligibility for egg freezing, which include: sufficient ovarian reserve (Day 3 FSH/LH and AMH within range) and under the age of 38 years is ideal.
VITRIFICATION
Vitrification is a relatively new technique used for the cryopreservation of both eggs and embryos. Unlike other techniques such as slow freezing, this technique avoids the formation of ice crystals altogether which can be detrimental to egg/embryo survival. Instead, through the vitrification process a glass-like state is achieved. With vitrification, the egg or embryo goes from room temperature to -196 Celsius in a matter of milliseconds, too quickly for any significant ice crystal formation.
This technique has revolutionized egg freezing. With this technique the success rate for egg survival after freezing has increased from as low as 6% to as high as 90%. As such the pregnancy rates from vitrified eggs has drastically improved.
ASSISTED HATCHING
The egg is surrounded by a layer of glycoproteins called the zona pellucida. This layer is critical for fertilization, however in order for successful implantation the developing embryo must first hatch out of its zona pellucida.
Naturally as the embryo develops the zona pellucida gradually gets thinner to facilitate the hatching process and increase implantation. Over the years studies have shown that the thinning process can be compromised by several factors including advanced maternal age and cryopreservation. As such, a technique called assisted hatching was developed where the zona pellucida is manually breached. Within the laboratory the embryologist will use a laser, a microtool or Tyrode’s acid to create a small hole in the zona pellucida. This technique is usually done on Day 2 or 3 of embryo development.
Studies have shown that with assisted hatching there is an increase in the implantation rate and may be indicated for the following reasons:
Age: the female is considered advanced maternal age (>37 yrs)
Embryo quality: Embryos with poor quality, including elevated fragmentation and slow embryo development
Zona quality: patients with an unusually thick zona pellucida
Previous IVF failure: patients with two or more failed IVF cycles
