Freezing embryos and freezing eggs are two separate processes each of which has their own advantages and disadvantages. Previously when slow freeze technology was used to freeze the eggs and embryos, frozen embryos survived the freezing and thawing process better in comparison to frozen eggs as embryos are less delicate than eggs. But due to the introduction of the process of flash freezing (vitrification), this difference has been eliminated. With this technique the survival rates of frozen embryos and frozen eggs are quite similar; about 90 percent of eggs and 95 percent of embryos survive.
Many individuals believe that the chances of a frozen embryo to result in a pregnancy in the future are more than those of a frozen egg. But that isn’t a true statistical comparison. Regardless of which method you are choosing, you require several eggs to get one embryo. You may freeze multiple eggs that you may then fertilize in the future to form a few embryos. Or you may fertilize the eggs after retrieving them and then freeze the few embryos that form. Either way, your number of chances of pregnancy in the future likely remains the same.
Reasons for freezing embryos and eggs
Egg freezing, also known as mature oocyte cryopreservation is a new technique for preserving fertility. The reasons why you may consider freezing your embryos and eggs are as follows:
You are over 30 years old but you haven’t met your right partner: Your fertility may start declining after the age of 28 years. This decline becomes very significant around 35 to 40 years of age. The decline in fertility may occur due to the aging of the eggs. As your eggs age, their quantity and quality may become lower and this may reduce the chances of your getting pregnant. Freezing your eggs may help preserve your fertility till the time you have met your right partner with whom you want to parent your child or until you want to become a single parent with the help of a sperm donor.
You don’t want to have a child now but you want to have a child (biological) in future: There may be many professional and personal reasons due to which you may not want to have a child while you are at the peak of your fertility. These may include military deployment, financial uncertainty, a recent divorce, job issues or other such challenges. These reasons may imply that you don’t want to conceive now but you want to have a child in the future. Frozen embryos and eggs are a good option in such scenarios.
You’re about to have treatment for cancer or any other illness, which may affect your fertility potential in the future: Preservation of fertility is a concern if you’re about to have chemotherapy, radiation therapy or surgery for cancer or any other illness as these treatments may harm your fertility. In such cases, frozen embryos (if you have a partner) or frozen eggs may enable you to have biological children after your treatment.
You suffer from other illnesses: Certain medical issues such as recurring or large ovarian cysts or severe endometriosis may limit your fertility. Chronic and progressive diseases such as kidney disease, sickle cell disease or systemic lupus erythematosus may also affect your fertility. In these cases, frozen eggs and frozen embryos may make it possible to have biological children through gestational surrogacy in case you are unable to carry your child due to health concerns.
How are embryos frozen?
The process starts by giving hormones and other medicines to the female for stimulating the production of multiple fertile eggs. In the hospital, a physician extracts the eggs utilizing an ultrasound machine. The eggs are then exposed to the sperms for fertilization, which may take 16 to 20 hours. This procedure is similar to a general IVF procedure. The eggs that are fertilized by the sperms develop into embryos. They are kept in incubators to develop and are frozen at a suitable time.
The main aim of freezing an embryo is to preserve it for future use. The major problem is the water present in the cells of the embryo. When this water freezes, it may form crystals. Due to this, the cell may expand, burst, and die. To prevent this from happening, the water present in the cells is replaced with a cryoprotectant (a protective substance). Your doctor places the embryos in a cryoprotectant before freezing them.
After the removal of water, the doctor uses one of the following two methods to freeze the embryos:
- Slow freezing: The doctor places the embryos in sealed tubes and then lowers the temperature in these tubes slowly to prevent the aging and damage of embryo cells. Frozen embryos may last much longer than fresh embryos. But the slow freezing process is time-consuming and it also needs expensive equipment.
- Vitrification: In this process of embryo freezing the embryos are frozen so rapidly that the water present in them doesn’t have enough time to form into ice crystals. This helps in protecting the frozen embryos and in increasing the survival rate while thawing.
After freezing, frozen embryos are kept in liquid nitrogen until their future use.
How long do frozen embryos last?
Theoretically, a frozen embryo may remain viable indefinitely. The frozen embryos are kept at temperatures of -321 degrees Fahrenheit in sealed containers. At such a low temperature, no biological processes including aging may occur. Certain countries have their own regulations about the duration of time for which an embryo may be stored. Furthermore, it is also expensive to freeze and store embryos. Hence, each clinic that does so has its own rules regarding what to do in case a woman can’t use her frozen embryos after a length of time.
The risks of freezing embryos
Any side effects and risks related to embryo freezing generally happen during the extraction of eggs from a female’s body.
Some of the common risks of frozen embryos are as follows:
- bloating or cramping
- feeling full
- changes in vaginal discharge
- overstimulation of the ovaries
Egg freezing procedure
There are multiple steps in the egg freezing procedure including induction of ovulation, retrieval of eggs, and freezing.
Ovulation Induction: at the start of your menstrual cycle, you may receive hormones that stimulate the ovaries to induce ovulation and produce multiple fertile eggs.
Several medicines that you may receive as an injection during this process include Follistim AQ, Bravelle, Gonal-f (follicle-stimulating hormone) or Menopur (human menopausal gonadotropins) or Lupron (gonadotropin-releasing hormone agonist) or Cetrotide (gonadotropin-releasing hormone antagonist).
Egg retrieval: this process requires sedation and it usually takes place in the doctor’s clinic. The doctor retrieves the eggs by the process of transvaginal ultrasound aspiration. It takes about 15 to 20 minutes to retrieve multiple eggs.
Freezing: after harvesting the unfertilized eggs, the doctor reduces their temperature to subzero levels to stop all the biological activity and preserve them. Your doctor may use cryoprotectants to help prevent the formation of ice crystals during the process of freezing.
One of the following two methods may be used for freezing eggs:
- Slow-freeze method: during this procedure, the doctor uses a low concentration of cryoprotectants in the beginning. They reduce the temperature gradually and as the metabolic rates in the eggs decline, they use a higher concentration of cryoprotectants.
- Vitrification: during this procedure, the doctor uses a high concentration of cryoprotectants at the beginning along with rapid cooling so that ice crystals don’t have enough time to form in the egg cell.
The risks of freezing eggs
The various risks of freezing eggs are as follows:
Conditions that occur due to using fertility medicines: in rare cases, using injectable fertility medicines such as a synthetic luteinizing hormone or follicle-stimulating hormone to induce ovulation may result in ovarian hyperstimulation syndrome. In this condition, your ovaries may become painful and swollen soon after egg retrieval or ovulation. Symptoms and signs include abdominal bloating, mild pain in abdomen, vomiting, nausea, and diarrhea.
Complications due to egg retrieval procedure: rarely, using an aspirating needle while retrieving eggs may cause bleeding, damage to the bladder, a blood vessel or bowel or infection.
Emotional risks: freezing of eggs may give false hope to a woman. Making a decision to freeze your eggs may give hope for your future, but there is no guarantee of success.
Freezing embryos vs. freezing eggs: which should you choose after all?
While comparing freezing embryos vs. freezing eggs, the latter offers simpler choices and more options for many females. Embryo freezing, in which a sperm fertilizes an egg before freezing, isn’t that much useful for single females or for females who aren’t quite sure that they want to have children with their current partner. When you are deciding between freezing embryos vs. freezing eggs, it’s important to keep in mind that while freezing eggs you don’t have to take co-parenting decisions at this moment. When you choose to freeze your eggs, you are preserving your fertility independently and this gives you so-called “reproductive autonomy.”
Furthermore, freezing eggs also offers a simpler path in the future if a couple or a female decides not to use the frozen material. Discarding a frozen embryo may become a moral dilemma for many females. On the contrary, discarding unfertilized frozen eggs is simpler.
Lastly, the cost of freezing eggs is lower in comparison to freezing embryo as the latter requires IVF before freezing. Hence, when you compare freezing embryos vs. freezing eggs, egg freezing is more accessible and an easier choice for most women who want to preserve their fertility for the future.
If you want to delay getting pregnant for the later stages of your life, freezing your embryos or eggs is a good option. There are many reasons why you may consider freezing your eggs and embryos. The process of embryo or egg freezing starts by giving hormones to stimulate the ovaries for ovulation and production of multiple eggs. Then the doctor extracts the eggs by using an ultrasound machine. If you want to freeze your eggs, then at this stage your eggs may be frozen using two methods: slow freezing or vitrification. To form embryos, the doctor may expose the eggs to the sperms for fertilization. When comparing freezing embryos vs. freezing eggs, freezing eggs is simpler and offers more options for women. It gives women reproductive autonomy as they may choose to preserve their fertility independently. Discarding a frozen egg is easier than frozen embryo if the frozen material isn’t used in the future. Furthermore, the cost of freezing eggs is lower compared to freezing embryos.