The Advantages of Frozen Embryos
In concordance with research at CCRM, studies from around the world have shown that in vitro fertilization (IVF) pregnancies following a frozen embryo transfer are more similar to natural conception pregnancies than fresh embryo transfer cycles resulting in:
Since frozen embryo transfers occur a significant amount of time after a woman’s ovaries were stimulated with medications, the hormone levels in the body have had time to return to normal, which mimics a more natural conception process appearing to have a positive impact on the health of the baby.
Researchers have also found that lengthening the time between administering the drugs and pregnancy lowers the chances of a woman’s risk of ovarian hyperstimulation syndrome (OHSS), a potentially fatal complication that can be triggered by taking certain fertility medications that stimulate egg production.
CCRM data, which was presented at the 2013 American Society for Reproductive Medicine (ASRM) annual meeting in October found that women of advanced maternal age (36-42 years) had a significantly higher live birth rate using frozen embryos in conjunction with comprehensive chromosomal screening (CCS) compared to fresh embryos. Women using frozen embryos for transfer had a live birth rate of 74.5 percent as compared to women using fresh embryos with a live birth rate of 53.7 percent. In addition, we observed only a 2.8 percent miscarriage rate following CCS with a frozen transfer compared to 18.5 percent in the fresh transfer group.
Preparing for FET
Before the transfer, all potential causes for infertility and implantation failure should be thoroughly investigated and treated. A uterine sonohysterogram (SHG) and mock (“trial”) embryo transfer will be performed to ensure that the uterine cavity appears normal and that embryo transfer will go smoothly without any surprises. Many of our patients will choose to undergo a newer test, called the endometrial receptivity assay/analysis (ERA), before FET. The ERA aims to identify the best time to transfer the embryo after progesterone first begins to rise. For approximately 70% of women, a standard embryo transfer after 5 days of progesterone will yield high rates of success. For almost one-third of women, however, the optimal window for implantation may be significantly earlier or later. Although implantation rates with IVF/PGT without ERA are generally quite high, a displaced window of implantation can be responsible for repeated implantation failures with chromosomally normal embryos. We have treated patients with multiple prior IVF failures who subsequently conceived with us doing their day 5 blastocyst transfer after just 3.5 days of progesterone and after 7 days of progesterone thanks to their ERA test. We, therefore, believe in sharing this option with patients before their first transfer attempt and will more strongly recommend it in specific cases.
The FET Cycle
On a basic level, the uterus needs just two hormones to prepare itself for embryo implantation: estrogen and progesterone. These hormones come from the ovaries in a natural cycle and can be provided by several pharmacological preparations in hormone-prepared FET cycles. Estrogen can be delivered via oral, vaginal, transdermal, and intramuscular routes. Progesterone is administered intramuscularly or vaginally. There is no one “best” way to prepare the uterus for FET in all patients. We perform a mix of traditional lupron downregulation cycles, no-lupron hormone therapy cycles, and natural/modified-natural cycle embryo transfers depending on our patients’ needs. Your CCRM fertility specialist will select the best protocol for you based on what is learned through the course of your evaluations and treatment.
In general, your FET cycle will start after a period begins. Baseline hormone assessments and an ultrasound will be performed. You will next have an ultrasound to check the lining of the uterus between the 12th and 14th day of your cycle. We would generally like to see an endometrium of 7-8 mm in thickness or more, but this measurement is highly individual. If we know how thick your lining can get in a stimulated cycle or an ERA cycle, these measurements can provide us with a reasonable expectation for your FET cycle. Once your optimal thickness has been achieved, you will start progesterone and embryo transfer will typically be performed 5 days later for blastocyst embryo transfer.
The Embryo Transfer
The embryo transfer procedure is not painful and does not require anesthesia. You are positioned in gynecologic stirrups, and a vaginal speculum is used to visualize the cervix. The cervix is cleansed with embryo transfer media, and excess mucous is cleared from the cervical opening. To perform the transfer, a soft catheter is passed through the cervical opening into the uterine cavity under abdominal ultrasound guidance. After carefully loading the embryo into the transfer catheter, your doctor will guide the catheter to the optimal depth and release the embryo into the uterus. Very often, you will see a small “twinkle” or “flash” on the ultrasound screen, indicating where the fluid surrounding the embryo was expelled from the tip of the catheter. The catheter is carefully withdrawn and then checked under a microscope to ensure that the embryo was not retained. The speculum is removed, and the procedure is complete. Prolonged bed rest is not necessary after the transfer, but many patients prefer to rest for 15 minutes following the procedure. Your progesterone is continued after the embryo transfer until your doctor indicates that it is safe to stop it. We perform a pregnancy test as early as 9 days after embryo transfer. When positive, you will be scheduled for a first obstetrical ultrasound around 6 weeks of pregnancy (about 3 ½ weeks after embryo transfer).
