Believe in yourselves, believe it is possible.
Call Today +91 9821 506 000
141, Powai Plaza, Powai, Mumbai.
Open Hours
Mon — Sat: 8 am — 5 pm, Sunday: CLOSED

Understanding Embryos

This guide helps you understand the different terminologies, their meaning, and success at SI (if specific) regarding:

Section 1 :     EMBRYO LIFE CYCLE

Day 0: Eggs are retrieved and combined with retrieved sperm

Day 1: Fertilisation should take place by now

Day 2: Embryo should be fertilized and may have 2-4 cells

Day 3: Embryo should now ideally have 4-10 cells

Day 4: Embryo should be now in morula stage (more than 16 cells, cannot be counted under microscope)

Day 5: Blastocyst stage of development


Section 2 :     EMBRYO GRADING

A grade is one way to identify the best quality embryos and to make decision of how many embryos to transfer, how many to freeze, and what to do with embryos that are not developing well.

Forty-eight hours after fertilization, the clinician evaluates the size and number of the divided cells, as well as the degree of fragmentation. It is preferable to have little or no fragmentation; the more fragmentation seen, the poorer the embryo quality.

The three level grading system for multi-cell embryos is evaluated in the following way:

Grade 1 / A / I: even cell division, little to no visible fragmentation

Grade 2 / B / II: even cell division, moderate fragmentation (about 20-40%)

Grade 3 / C / III: uneven cell division, excessive fragmentation (more than 50%)

Grade ‘1’ or ‘A’ or ‘I’ includes the best quality embryos. Statistically, these have a higher chance of implantation than those of grade 3 or ‘C’ or ‘III’.


Section 3 :    EMBRYO TRANSFER

Embryo transfer refers to a step in which embryos are placed into the uterus.

As per your wish and your attending doctor’s advice between one and maximum three of the best quality embryos are transferred to the woman’s womb (as per ICMR guidelines). An embryo must successfully attach itself to the wall of the womb (uterus) for pregnancy to begin.

The embryos are generally transferred 2-3 days after fertilization and may then be at the 4-10 cell stage, or they are transferred around day 5, when they have reached the blastocyst stage.

The doctor doing the embryo transfer inserts a speculum into surrogate’s vagina. A fine tube (catheter) is passed through the cervix, normally using ultrasound guidance. The embryos are passed down the tube into the womb.

This is normally a pain-free procedure and usually no anesthesia is necessary.

Complete bed rest is advised during the few days after embryo transfer.



Depending on how many embryos are produced and their quality, embryos can be left in the laboratory for 5–6 days.A blastocyst is an embryo that has developed for around five days after fertilization.

It possesses an inner cell mass (ICM), and an outer layer of cells surrounding the inner cell mass and a fluid-filled cavity known as the blastocoele. The human blastocyst comprises 70-100 cells. An enzyme of the cells on the exterior, erodes outer lining and creates a site for implantation. (There by increased chances of success rate).

Pros and cons of Blastocyst Transfer

Under the standard IVF culture conditions, only about 20 to 50% of human embryos progress to the blastocyst stage after 5 days of culture. The low rates are usually due to the inherent “weakness” of human embryos

Thus, it is not really advised in cases where we have less number of embryos, or higher age of the eggs (mother). Keeping embryos for Blastocyst may also mean fewer embryos left to freeze.

Blastocyst transfer can result in a higher likelihood of becoming pregnant when compared with 2–3 day embryo transfer. This is with the assumption that if the embryo has already grown till day 5, the embryo is good, and should grow further.

Blastocyst Transfer is more expensive to due media, culture, incubation technique.



At SI, we also do sequential transfers. We transfer 1-2 embryos on day 2 / 3 and keep 2-3 embryos for blastocyst culture. There are multiple outcomes:

If we get 1 Blastocyst, we transfer that on day 5 (called sequential transfer). If we do not get any blastocysts, we have already put in some embryos inside the uterus. If we get all embryos becoming blastocysts, the rest of the blastocysts are frozen.


There are some embryos put in uterus. We do not put many embryos but few “at risk” to become blastocyst.



Section 6 :    EMBRYO FREEZING

Cryopreservation of embryos is the process of freezing an embryo at sub-zero temperatures formed from fertilization till the blastocyst stage. The main techniques used for embryo cryopreservation is vitrification, which is far superior to other Slow freezing technique.


It gives you the option of using the frozen embryos in future, without having to go through the risks of expense, inconvenience of using fertility drugs and undergoing egg collection again.

If you are facing medical treatment that may affect your fertility, embryo freezing is currently the most effective way to preserve the fertility.

Success in Surrogacy

In current state of the art, embryos having undergone cryopreservation implant at the same rate as equivalent fresh counterparts.

In surrogacy, it is more ideal, as we prepare the surrogate uterine lining, and only when the lining is ready, do we thaw embryos and transfer them to surrogate. Unlike in fresh cycle: the surrogate lining HAS to be prepared as per the egg donor (mothers) dates, egg pick up date, there by not giving us the optimal chance of preparing optimal uerine lining for embryo transfer.

The outcome from using cryopreserved embryos has uniformly been positive with no increase in birth defects or development abnormalities.

Your chances of becoming pregnant with a thawed frozen embryo are not affected by the length of time the embryo has been stored for. Once frozen, embryos stay in the same state for 1 minute or 1 year, without any changes.


Not all embryos will survive freezing and eventual thawing when they come to be used.  Though our lab has more than 95% recovery rate. You can store embryos for a maximum period of 5 years.


Section 7 :    b-HCG (TWO WEEK WAIT)

Even before you settle at your home, the TWW unsettles you in your mind. Post ET, the SM is kept at the clinic till the first bHCG (Pregnancy) test is done. This helps to ensure that SM is resting, taking medications, is under medical supervision, not doing home chores, and is physically away from husband.

The beta (bHCG) test is usually done 12 days post embryo transfer. Not considering Sundays/holidays, the blood report is made available only on next day. We should either give you a call or email you the result.

This can be stressful, exciting and a nerve wracking time. We suggest that you should keep yourself busy with your work or reading. At any point, please remember you are never away from SI. Hoping that you have a positive pregnancy test, you will then follow the My Pregnancy Cycle chart and other guides for monitoring the pregnancy.


We wish you all the best for a positive pregnancy result and experience. If you have any specific concern, query, please ask us at

Request an appointment