About Embryo grading and success rate | Slow growing embryos in IVF | Ask the embryologist

What are the Common Questions that patients ask while undergoing IVF Treatment

I am the Senior Embryologist at Malpani Infertility Clinic. The IVF lab plays an extremely important role in the success of your IVF treatment, and we are very proud of the work we do in helping you to have a baby.
I'll be happy to answer any queries you have! Please email me at
When we show our patients their embryos in our lab, this is often a highly emotional moment for them.
Here are some of the common questions they ask. I'd like to share my answers.

1) How do you grade embryos?
Grading Multicellular Stage Embryos (Day 2 and Day 3 embryos) :

There are 3 factors which are considered while grading the multicellular stage Embryos:

a) Cell number

  • Embryos should be at 2 to 4 cells at 48 hours after egg retrieval (Day 2 embryos) and preferably about 6 to 10 cells by 72 hours (Day 3 embryos)
  • The cells in an embryo are also referred to as "blastomeres"

2-Cell (Day 2 embryo)

4-Cell (Day 2 embryo)

6-Cell (Day 3 embryo)

10-Cell (Day 3 embryo)

b) Cell regularity - degree of regularity of size of blastomeres

  • It is generally best if the size of the individual cells (referred to as blastomeres) in the embryos are similar in size.
  • If they are not, it is better if they are close to the same size, as compared to very different in size.
  • A Grade A embryo is one which has equal-sized cells in it.
  • 4-Cell Embryo with irregular Blastomeres

4-Cell Embryo with irregular Blastomeres

c) Degree of fragmentation

  • Fragmentation is a process where portions of the embryo's cells have broken off and are now separate from the nucleated portion of the cell.
  • Fragmentation in human embryos is quite common and many beautiful babies have resulted from implantation of embryos with fragments.
  • A grade A embryo is the one that has no fragmentation or less than 10% fragmentation. These are the best and have the best chances of implanting.


10-Cell Grade A embryo

- Regular Blastomeres.
- No Fragmentation.


10-Cell Grade B embryo

- Regular Balstomeres.
- > 10 % Fragmentation.


8-Cell Grade C embryo

- Irregular Blastomeres.
- > 10 % Fragmentation.


8-Cell Grade D embryo

- Irregular Blastomeres.
- > 20 % Fragmentation.

These are the worst and have poor chances of implanting.

Grading Blastocyst Stage embryos (Day 5, Day 6 embryos) :

  • A Blastocyst is an embryo that has developed to the point of having 2 different cell components and a fluid cavity.
  • Human embryos, in culture in an IVF lab, or developing naturally in the female body, usually reach the blastocyst stage by day 5 after fertilization.

A Blastocyst is graded considering 3 factors :

  1. Size of the Cavity, Expansion, and Hatching status.
  2. Inner Cell Mass (ICM) Quality.
  3. Trophectoderm (TE) Quality.
  • Inner Cell mass is marked as "ICM"
  • The cavity is Marked as "C"
  • Trophectoderm is Marked as "T"

Early Blastocysts

  • The cavity is very small or fills less than ½ embryo's volume.
  • The grade for Cavity in Early Blastocysts will be 1.
  • The Grade for Early Blastocyst generally will be 1AA, 1AB, 1BA.

Intermediate Blastocysts

  • The Cavity fills more than ½ Embryo's volume or completely fills the embryo's volume.
  • The Grade for Cavity in Intermediate Blastocysts will be 2 or 3.
  • The Grade for Intermediate Blastocysts generally will be 2AA, 2AB…… or 3AA, 3AB.

Expanded Blastocysts

  • The Embryo Expands, The Cavity completely fills the Embryo's volume.
  • The Grade for Embryo will be 4.
  • The Grade for Expanded Blastocysts generally will be 4AA, 4AB, 4BB.

Hatching Blastocysts

  • The embryo hatches mean comes out of the shell called Zona.
  • The Grade for Embryo will be 5
  • The Grade for Hatching Blastocyst generally will be 5AA, 5AB.

Completely Hatched Blastocysts

  • The embryos come completely out of the zona.
  • The grade for the embryo is 6.
  • The grade for Hatched Blastocyst generally will be 6AA, 6AB.

2) Maximum how many embryos can be transferred?
We transfer 2 blastocysts on Day 5. We recommend Single Blastocyst transfer. This is now our preferred option. We try to individualize this for each patient, taking into account many variables such as Patient's Age and Previous History (multiple failed cycles)

3) Why sometimes the Embryo quality is Bad?
The embryo quality depends on 3 factors, Sperm, Egg, and Lab conditions. If other patient's embryos are good, we can't blame Lab conditions for poor quality. So it is usually poor Egg quality which is responsible for poor embryos. Poor sperm usually do not affect embryo quality after ICSI

4) Why sometimes the embryos grow slow? What are the chances of pregnancy with slow-growing embryos?
Since the embryos are growing slow, their viability is suspected. But they can still become a baby. But the Probability is less compared to good ones.

5) Why sometimes the fertilization rate is poor?

  1. IVF – sperm? sperm function. Next ICSI
  2. ICSI :
    1. If egg quality wasn't good. If most of the eggs were immature.
    2. Sperm quality should not affect the fertilization rate after ICSI.

6) If the embryo Quality is bad, what are the chances of pregnancy?
Even Poor Quality embryo can become a baby. The probability for it to become a baby is lesser compared to a good quality embryo.

7) If 3 blastocysts are transferred, what are the chances of multiple pregnancies?
The chances of multiple pregnancies is more with 3 blastocysts, being transferred.

8) Does Day 5/6 Embryo Transfer (Blastocyst) help increase the chances of pregnancy?
No. Blastocyst Transfer doesn't increase the Pregnancy rate. But it enables us to transfer less no. of embryos compared to Day 2/3 Transfer, thereby reducing the chances of multiple pregnancies.

9) Does Assisted Hatching help increase the chances of pregnancy?
No. Assisted Hatching doesn't increase the pregnancy rate. Zona of an embryo has 2 layers, an inner layer, and an outer layer. When we do assist hatching, we zap the outer layer. But the outer layer would anyways be very thin. And zapping inner layer is risky, as a blastomere could easily come out while handling the embryo.

10) Do we need to do genetic testing before embryo transfer?
Genetic testing or PGD is not mandatory before Embryo transfer. It is done only if there is a risk of any genetic disorder to the resulting baby.

11) Will sequential embryo transfer help increase the chances of pregnancy?
Yes. Sequential Embryo transfer does help increase the pregnancy rate. But it also increases the chances of multiple pregnancies. So Selection of the patient for Sequential embryo transfer is critical such as :

  1. Patients Age – more than 35
  2. Grade of Embryos.
  3. Previous History- Repeated failed cycles.

12) How do you ensure that the eggs and sperms of different patients don't get mixed?
Each and every biological cell is labeled with a patient's name. For e.g.

  1. The Container for Semen collection is labeled with both Husband and wife's name before it is given to the patients.
  2. The dishes in which the eggs and embryos are kept are labeled with patients' names.
  3. The chambers of Incubators are labeled with patients' names. The labels are discarded once the patient's embryo transfer is over.
  4. The embryologist and the doctor are informed by the patient's name at the start of every procedure i.e. Ovum Pick Up and Embryo Transfer.
  5. The Nurse stands as witness, while the Embryologist loads embryos and handing over the catheter to the doctor for transfer.

13) How long can we store the embryos once we freeze them?
There is no time limit for the storage of frozen embryos. The embryos can be stored for years, once they are frozen. However Proper maintenance of cryocans in which the embryos are stored should be ensured.

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Authored by : Dr Aniruddha Malpani, MD and reviewed by Dr Anjali Malpani.