Frozen Embryo Transfer
This is the name given to the process in which the embryos formed and frozen in an IVF cycle, are replaced in the uterus in a subsequent month.
Patient is seen on day 1 or 2 of periods.
We do a transvaginal scan to confirm the absence of any cysts.
Medication may be started in case of a hormonal cycle to prepare the lining of the
Ultrasound monitoring of the endometrial lining is done starting about day 10 of cycle
Once the lining reaches a satisfactory thickness, progesterone is started,
Embryo transfer is planned after 3-5 days of progesterone depending on whether day 3 or day 5 embryos need to be replaced.
Embryo transfer is done under ultrasound guidance.
Luteal phase support with injections or medicines is advised for two weeks.
Beta hCG blood test is taken after 12 -14 days of transfer.
What are the different types of FET?
Though the preparation of the endometrium may be done by different methods, the rest of the process after the lining is found to be satisfactory, remains the same in all methods.
1. NATURAL CYCLE:
In a lady with regular periods, we may choose to give no medications at all and simply follow her natural pattern on ultrasound starting from day 8-10 of her cycle. Once ovulation occurs naturally, we plan for FET.
2. MODIFIED NATURAL CYCLE:
This is almost similar to the natural cycle except that we give hCG injection for ovulation and time the FET accordingly.
3. STIMULATED CYCLE:
In a woman with anovulatory cycles or irregular periods, we may start medicines like letrozole for ovulation
induction on day 3 of periods and start a follicular study as usual on day 10 of her cycle.
Once the follicle reaches a certain size and the endometrial lining is thick, we give injection to release the egg and plan for embryo transfer.
4. HRT CYCLE:
We start oestrogen tablets from day 2 of periods and start ultrasound from day 10 of cycle to assess endometrial thickness(ET). Once the ET is sufficient, we give progesterone and plan for FET. Here, ovulation is inhibited by the use of oestrogen.
5. ANTAGONIST CYCLE:
This is almost the same as the HRT cycle but we gave an antagonist injection in the previous month to
suppress the woman's natural hormone production.,
Once periods start or after confirming suppression of endogenous hormone production, we start oestrogen tablets.
We usually expect a minimum of 8 mm thickness before replacing the embryos.
The lining may be unsatisfactory in one month and pick up in other months or with
different methods of endometrial preparation as discussed before. In few women
with persistently thin endometrium, we may have to rule out few causes like;
A. Endometritis due to an active infection.
B. Damage of lining due to previous genital tuberculosis.
C. Damage of lining due to previous trauma or surgery.
The endometrial lining in an ongoing IVF cycle may be suboptimal due to a state
of increased oestrogen production and hence where there are multiple follicles
developing, we prefer to freeze all the embryos and replace them at a later
Also, in such patients, we have the very important advantage of avoiding OHSS when we give an agonist trigger, freeze all and plan FET at a later date.
When the endometrial lining is more than 14-15 mm, the pregnancy rates may
decrease and hence it is better to postpone transfer and rule out any pathology
in the uterus like
A. Presence of endometrial polyps.
B. Presence of submucosal fibroids.
C. Endometrial hyperplasia.
D. Incomplete shedding of the endometrium.
A minimum of 8 days of oestrogen intake is advisable for adequate endometrial
Though maximum duration has been reported upto even 40-60 days, usually we give for a period of 15-25 days before deciding to transfer or cancel the cycle.