In vitro fertilization (IVF) is a treatment where eggs are fertilized with sperm in the laboratory setting. The fertilized eggs grow in heated incubators to become embryos, which are then transferred to the mother’s uterus (fresh), or they are frozen (cryopreserved) for later use in future cycles.
In previous years, the prevailing thought in assisted reproductive technology (ART) was that fresh embryo transfer yielded higher success rates of pregnancy than frozen embryo transfers. However, according to the Society of Assisted Reproductive Technology (SART), for women age 35 years and older, the percentage of transfers that result in live births is higher with frozen embryo transfers. One factor contributing to success rates for pregnancy is the mother’s age at the time these eggs are frozen.
The Embryo Transfer Procedure
For the woman, the embryo transfer is much like a Pap smear. There is no pain, so drugs are not required. After drinking to obtain a full bladder, the doctor inserts a small catheter with the embryos through the end opening of the uterus (cervix) and up to the middle of the uterine cavity.
Using ultrasound guidance, the doctor watches on a monitor so the tip is advanced to the proper position. The embryos are then placed into the lining of the uterine cavity, which is called the endometrial lining. The catheter is the slowly retracted from the uterus.
Pros of Fresh and Frozen Embryo Cycles
- With a fresh IVF cycle, the woman must take hormone treatment to regulate her menstrual period, stimulate ovulation, and assist with egg maturation. Once the eggs are mature, they are fertilized in the laboratory setting with the male partner’s sperm. A few days later, the embryos are transferred to the female partner’s uterus.
- When a frozen embryo is used for an IVF cycle, the woman doesn’t have to take medicines for ovarian stimulation or egg retrieval, because it has been done previously. However, she does have to take estrogen and progesterone to prepare the uterus’ lining to receive the embryo.
- Many women report that using frozen embryos for future IVF cycles is less stressful, because you do not have to go through the egg retrieval process.
- There is a shorter timeframe from choosing a donor if frozen eggs are used for transfer.
Cons of Fresh and Frozen Embryo Cycles
- With a fresh cycle, you have to take medications for ovarian stimulation, which costs may range from $4,000 to $9,500.
- If you fail on the first IVF cycle, you will have to go through the entire process again if you wish to use a fresh embryo the second time.
- A large clinical study found that the pregnancy success rate is 30% higher when using frozen embryos than fresh transfers.
- The cost per cycle is more when fresh eggs are used for subsequent IVF cycles.
Success Rates using Frozen Donor Eggs
The success rate using frozen donor eggs depends on several factors, such as:
- The ability of the clinic to perform effective freezing of the eggs, as well as thawing.
- The quality of the donor eggs.
- The number of embryos to be transferred.
- The number of eggs thawed.
- The expertise of the IVF specialists.
- The quality of the IVF program.
Variables that affect Success Rates
Several factors affect the success rates of both fresh and frozen embryos. These variables include:
- Embryo survival after the freezing and thawing processes is related to the quality of the embryo.
- During fresh cycles, subtle rises in progesterone levels before administration of hCG (pregnancy hormone) can affect implantation rates.