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Understanding embryo transfer in IVF: fresh VS frozen
Embryo transfer refers to the step of invitro fertilization where the fertilized embryos are placed inside the uterus.
Embryo transfer is an art and a delicate procedure, if not done with experienced hands it might lead to IVF failure.
Studies have shown that 25% of embryos transferred inside the uterus are subsequently found inside the vagina (wrong position), that’s why gynecologists consider embryo transfer the most critical point of IVF.
What are the factors that affect embryo implantation?
- Timing
- Uterine receptivity
- Embryo quality
Fresh embryo transfer:
- The transfer is done in the same cycle as egg retrieval
- It is done 3-5 days after fertilization
- The advantage is that it doesn’t require embryo freezing or thawing
- The disadvantages are:
** it is done during a time where the body hormones are not induced naturally which might affect uterine lining
**higher risk of ovarian hyperstimulation
- Fresh embryo transfer is preferred when the ovarian response is good and there are no risk factors of ovarian hyperstimulation
Frozen embryo transfer:
- The embryos are cryopreserved after fertilization and transferred during another cycle
- The advantage is that the uterus is more naturally prepared by natural hormones in subsequent cycles and lower risk of ovarian hyperstimulation
- The disadvantages are that it leads to longer treatment periods and embryo freezing and thawing might affect embryo survival rates
- It is preferred when there is high risk of ovarian hyperstimulation and when endometrial lining is found to be thin during the fresh cycle.
Are pregnancy rates higher with embryo freezing?
Some studies showed that because when transferring frozen embryos, the uterine environment is more natural hormonally, but this doesn’t apply to all women as some ladies have higher pregnancy rates with fresh embryo transfer.
Each case has to be individualized and studied thoroughly to decide what’s best for it.
Frozen embryo transfer leads to lower rate of:
- Preterm birth
- Low birth weight
Because the uterine environment is more naturally prepared
So, to sum up, how do we decide if we should do fresh embryo transfer or frozen embryo transfer?
By studying the following factors:
- Maternal age
- Ovarian reserve
- Endometrial thickness and quality
- Number and quality of embryos
- Risk of ovarian hyperstimulation syndrome
- Doctor assessment of the case
- Patient preference
Dr Najeeb Layyous F.R.C.O.G
Consultant Obstetrician, Gynecologist and Infertility Specialist
