Embryo

Going into IVF conversations with a baseline understanding of the definitions involved can help prospective parents know what questions to ask, and how to interpret the answers.

What Is Involved In the Embryo Transfer Process?

Conceiving through in vitro fertilization (IVF), or other assisted reproductive technology, is a multifaceted process that involves several steps. Once eggs have been retrieved, successfully fertilized, and the embryos have developed, the embryo transfer procedure is planned by the reproductive endocrinologist (REI, also called RE). IVF embryo transfer processes vary depending on factors that include whether fresh or frozen embryos are used and how many embryos are planned for transfer. Successful embryo implantation into the uterine cavity requires careful planning before the actual transfer procedure itself, and possibly a few lifestyle adjustments for the woman during the weeks immediately following the procedure.

How Many Embryos to Transfer for IVF? 

After an egg retrieval for a fresh cycle, or when contemplating a frozen embryo transfer, women often wonder how many embryos should be placed into the uterus. Usually, single embryo transfer (SET) is promoted, especially if an embryo is genetically tested (undergoes pre-implantation genetic testing, PGT). However, there are cases where a patient may want to transfer two or more embryos. Examining the pros and cons of multiple embryo transfer can help women make an informed decision.

How to Read PGT Results

Preimplantation genetic testing (PGT) is the general term for genetic testing performed on embryos produced by in vitro fertilization (IVF) before the embryos are transferred to the uterus. The purpose of PGT is to improve the chances of having a successful embryo transfer.

Genetic testing does not impact or change the genetics of an embryo, but it does give doctors and prospective parents more information and may help them select the most viable embryos for transfer.  

There are three types of PGT: PGT for monogenic disorders (PGT-M), PGT for structural chromosomal rearrangements (PGT-SR), and PGT for aneuploidy (PGT-A). PGT-A is the most routine type performed and as such should be understood by prospective parents.

Embryo Thawing for Preimplantation Genetic Testing (PGT)

Embryo freezing, also known as cryopreservation, is an assisted reproductive technology which involves storing preimplantation-stage embryos created through in vitro fertilization (IVF). Cryopreservation is done at extremely low temperatures (-196°C or -321°F) to halt embryo development and preserve their vitality, in a process called vitrification. Following vitrification, these embryos can be safely cryopreserved (frozen) for extended periods until they are thawed for transfer back to the uterus (frozen embryo transfer).  

Cryopreservation is necessary when preimplantation genetic testing (PGT) is chosen. Typically, fresh embryos undergo a biopsy before freezing to allow time for the genetic tests to be conducted. However, there are cases where patients decide that they want to perform genetic testing of previously frozen embryos. In these circumstances, frozen embryos must be thawed for biopsy, then refrozen until further use.  This means that the embryos will undergo an additional freeze-thaw round compared to the typical protocol.

Fresh vs. Frozen Embryo Transfer

An embryo transfer is usually the final step in the process of in vitro fertilization (IVF), where the embryo is transferred to the patient’s uterus. The embryos used in this procedure may either be fresh or thawed (after being frozen).

During IVF, mature eggs are fertilized, either by conventional IVF (insemination) or intracytoplasmic sperm injection (ICSI), after which the resulting embryos are grown in an incubator in the embryology laboratory. An embryo transfer is the procedure whereby one or more of the embryos that has been grown in the lab setting is then transferred from culture media into the patient’s uterus, in the hopes of initiating a pregnancy.  

Fresh embryo transfers are those in which the embryo was fertilized after the ovarian hyperstimulation and egg retrieval process, then transferred in the same cycle. As such, the embryo has never been frozen.i Alternatively, embryos can be frozen and preserved by a process called cryopreservation, and then stored to be transferred in a subsequent cycle. This is known as a frozen embryo transfer (FET) and requires the cryopreserved embryo to be thawed before transferring into the uterus.ii

How Many Embryos to Transfer for IVF? 

After an egg retrieval for a fresh cycle, or when contemplating a frozen embryo transfer, women often wonder how many embryos should be placed into the uterus. Usually, single embryo transfer (SET) is promoted, especially if an embryo is genetically tested (undergoes pre-implantation genetic testing, PGT). However, there are cases where a patient may want to transfer two or more embryos. Examining the pros and cons of multiple embryo transfer can help women make an informed decision.

Chromosomal Analyses of Embryos and Fetuses

Chromosomes are made up of DNA and genes that determine multiple aspects of a human’s makeup. Chromosome analyses are often performed in an attempt to give a healthcare provider more insight into a range of issues, from potential genetic conditions to what may be causing recurrent miscarriage. Embryonic and fetal genetic testing may be recommended or pursued for a variety of reasons. Sometimes, individuals or couples have genetic conditions that run in their families, in which case in vitro fertilization (IVF) with preimplantation genetic testing (PGT) can help select embryos that do not carry this condition. In other cases, those attempting to conceive or who have had multiple pregnancy losses may pursue genetic testing of an embryo to help ascertain a cause. Genetic testing can also give an early glimpse into the sex of the fetus as well as whether the fetus has extra/missing chromosomes that could cause conditions such as Down or Turner Syndromes.

Complete Guide to Dilation and Curettage (D&C)

A dilation and curettage (D&C) is a surgical procedure that is used to remove tissue from the uterus, and while it is performed for a variety of reasons including diagnostic purposes, it is typically used following a miscarriage or for elective termination of a pregnancy. An understanding of what to expect before, during, and after a D&C is beneficial for navigating this procedure, as well as to learn about potential risks and alternative treatments.

How to Read PGT Results

Preimplantation genetic testing (PGT) is the general term for genetic testing performed on embryos produced by in vitro fertilization (IVF) before the embryos are transferred to the uterus. The purpose of PGT is to improve the chances of having a successful embryo transfer.

Genetic testing does not impact or change the genetics of an embryo, but it does give doctors and prospective parents more information and may help them select the most viable embryos for transfer.  

There are three types of PGT: PGT for monogenic disorders (PGT-M), PGT for structural chromosomal rearrangements (PGT-SR), and PGT for aneuploidy (PGT-A). PGT-A is the most routine type performed and as such should be understood by prospective parents.

Stages of Embryo Development from Fertilization to Blastocyst

Read through the different stages of embryo development and what happens after egg retrieval in IVF. Day-by-day outlines and more from researchers in the field.

What Is Involved in the Embryo Transfer Process? 

Conceiving through in vitro fertilization (IVF), or other assisted reproductive technology, is a multifaceted process that involves several steps. Once eggs have been retrieved, successfully fertilized, and the embryos have developed, the embryo transfer procedure is planned by the reproductive endocrinologist (REI, also called RE). IVF embryo transfer processes vary depending on factors that include whether fresh or frozen embryos are used and how many embryos are planned for transfer. Successful embryo implantation into the uterine cavity requires careful planning before the actual transfer procedure itself, and possibly a few lifestyle adjustments for the woman during the weeks immediately following the procedure.

How Are Embryos Graded?

In order to increase the chances of a successful pregnancy, embryo grading is completed by an embryologist during an in vitro fertilization (IVF) cycle. Assessing embryos for quality at specific stages of embryo development can be a valuable tool in reproductive medicine to help the doctor decide which embryo to transfer first (when there is more than one embryo available for transfer). Understanding what takes place during embryo grading is important, in that it can help patients determine what their next steps in the IVF process might be.

Preimplantation Genetic Testing (PGT)

Preimplantation genetic testing (PGT) is the general term for genetic testing performed on embryos produced by women undergoing in vitro fertilization (IVF) before transfer to the uterus. PGT aims to improve the chances of having a successful ongoing pregnancy after embryo transfer. While genetic testing does not impact or change the genetics of an embryo, it gives doctors and prospective parents more information and may help them select the most viable embryos for transfer.