One of the aspects that raises the most questions when starting an in vitro fertilisation (IVF) treatment is embryo quality. Patients may hear phrases such as “we have a grade A embryo”, “our best embryo is an AA blastocyst” or “we are going to transfer a good-quality embryo”. But what do these classifications actually mean?
Embryo assessment plays an essential role in identifying those with the greatest potential for implantation and pregnancy. However, it is important to remember that embryo grading provides an estimate based on morphological features and developmental progress. An embryo with an excellent grade does not guarantee pregnancy, just as an embryo with an intermediate grade may still result in the birth of a healthy baby. Each case must always be assessed individually.
Below, we explain how embryos develop during the first few days after fertilisation, the criteria embryologists use to assess them, what grades A, B, C and D mean, and how the embryo selected for transfer is chosen during assisted reproduction treatment.
An embryo develops following the fertilisation of an egg by a sperm cell. In assisted reproduction, fertilisation can take place through conventional in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI).
Once the egg has been fertilised, it begins a continuous process of cell division that drives embryo development. During the first few days of culture in the laboratory, embryologists carefully monitor how each embryo develops, assessing its characteristics and identifying those with the greatest implantation potential.
Embryos develop rapidly during the first few days after fertilisation.
| Day of development | Day of development | Características principales |
| Day 1 | Zygote | Embryologists check that fertilisation has occurred normally. The embryo should have two pronuclei — one maternal and one paternal — and two polar bodies. |
| Day 2 | Cleavage-stage embryo | The embryo usually has between 2 and 4 cells. The number of blastomeres, cell symmetry, fragmentation and any signs of multinucleation are assessed. |
| Day 3 | Cleavage-stage embryo | The embryo will usually have between 6 and 10 cells, with around 8 cells considered the expected stage of development. This is an important point for assessing embryo quality. |
| Day 4 | Morula | The cells begin to compact and become increasingly difficult to distinguish from one another. The embryo continues developing towards the blastocyst stage. |
| Day 5 | Expanded blastocyst | The inner cell mass, which will develop into the baby, the trophectoderm, which will mainly form the placenta, and the blastocoel can now be distinguished. Day 5 is the most common day for embryo transfer. |
| Day 6 | Expanded blastocyst | Some embryos reach the blastocyst stage one day later. Although, in general, Day 6 blastocysts have slightly lower implantation rates than Day 5 blastocysts, they still have a significant and realistic chance of resulting in pregnancy. |
Not all embryos develop at exactly the same rate. Some reach the blastocyst stage on Day 5, while others do so on Day 6. This does not necessarily mean that Day 6 embryos are not viable. Developmental timing should always be considered alongside the morphological assessment carried out by the embryology laboratory.
Embryo grading involves assessing their appearance under the microscope as well as how they progress during culture. There is no single universal grading system, although many laboratories follow recommendations from organisations such as the European Society of Human Reproduction and Embryology (ESHRE), the Spanish Association for the Study of Reproductive Biology (ASEBIR) and Alpha Scientists in Reproductive Medicine.
Embryologists assess several parameters:
In many laboratories, early-stage embryos on Days 2 and 3 are classified using a straightforward grading system.
| Embryo grade | Characteristics | Reproductive potential |
| Grade A | Symmetrical cells, minimal or no fragmentation and appropriate development. | Very high. These embryos have the most favourable morphological prognosis. |
| Grade B | Good-quality embryos with minor differences in cell symmetry or slight fragmentation. | High. Many successful pregnancies result from grade B embryos. |
| Grade C | Moderate fragmentation or less uniform development. | Intermediate. These embryos can implant and result in an ongoing pregnancy. |
| Grade D | Significant morphological or developmental abnormalities. | More limited, although assessment must always take the individual clinical context into account. |
Once an embryo reaches Day 5 or Day 6, the A, B, C and D grading system is generally no longer used in the same way. At this stage, blastocysts are commonly assessed using the Gardner and Schoolcraft grading system, which considers three aspects.
1. Early blastocyst. The blastocoel is beginning to form.
2. Blastocyst with a clearly defined but still relatively small cavity.
3. Full blastocyst, with the cavity occupying almost the entire embryo.
4. Expanded blastocyst. The cavity has increased in size and the zona pellucida is beginning to thin.
5. Hatching blastocyst. The embryo is beginning to emerge from the zona pellucida as it prepares for implantation.
6. Fully hatched blastocyst. The embryo has completely emerged from the zona pellucida.
Some common examples include:
| Grade | What it means |
| 4AA | An expanded blastocyst with an excellent inner cell mass and excellent trophectoderm. This is one of the most favourable morphological grades. |
| 5AA | A blastocyst that has started to hatch and has excellent-quality inner cell mass and trophectoderm. |
| 4AB | An expanded blastocyst with an excellent inner cell mass and good-quality trophectoderm. |
| 3BB | A full blastocyst with good-quality inner cell mass and trophectoderm. It is still considered an embryo with good implantation potential. |
| 5BC | A hatching blastocyst with a good-quality inner cell mass and lower-quality trophectoderm. Its implantation potential may be lower, although it can still result in pregnancy. |
A more favourable morphological grade is generally associated with a higher likelihood of implantation, but it does not guarantee pregnancy. Similarly, blastocysts graded BC can result in the birth of a baby. Morphological quality is only one of the factors considered by the medical and embryology teams when selecting an embryo for transfer.
The aim of the embryology laboratory is to identify the embryo with the greatest implantation potential. However, the decision is not based solely on morphological grading. Other factors are also taken into account, including:
No. Embryo quality is one of the most important factors influencing the chances of pregnancy, but it is not the only one. Even an embryo with excellent morphology may fail to implant because of chromosomal abnormalities that cannot be detected under the microscope, endometrial factors or other biological factors that cannot be assessed through morphology alone. Likewise, embryos with intermediate grades have resulted in thousands of successful births.
Alpha Scientists in Reproductive Medicine & ESHRE Special Interest Group of Embryology.
The Istanbul Consensus Workshop on embryo assessment: proceedings of an expert meeting.
Human Reproduction.
2011;
1270-1283
International consensus on embryo evaluation criteria:
https://academic.oup.com/humrep/article/26/6/1270/2914112
European Society of Human Reproduction and Embryology.
Good practice recommendations for add-ons in reproductive medicine.
European Society of Human Reproduction and Embryology (ESHRE).
2023;
Recommendations on good practice for add-ons in reproductive medicine:
https://www.eshre.eu/?utm_source=chatgpt.com
Gardner DK., Schoolcraft WB.
In vitro culture of human blastocysts.
CRC Press.
1999;
Capítulo sobre cultivo in vitro de blastocistos humanos:
Alpha Scientists in Reproductive Medicine & European Society of Human Reproduction and Embryology.
The Vienna Consensus: assessment of human embryos.
Human Reproduction Open.
2024;
Update on the consensus regarding the evaluation of human embryos:
https://academic.oup.com/hropen/article/2024/1/hoae001/7581708
Privacy Policy
IVF-LIFE, hereby informs you of its privacy policy applied to personal data. The use of the website does not imply that the user must provide any information regarding their identity, and cannot be associated with a specific user by the company. In the event that personal data is provided, this data will be collected and used in accordance with the limitations and rights set out in the aforementioned regulation.
WHO IS RESPONSIBLE FOR THE PROCESSING OF YOUR DATA?
DATA CONTROLLER: IVF SPAIN ALICANTE S.L.U (hereinafter IVF-Life)
CIF: B-54973227
Postal Address: Avenida de Ansaldo, no. 13, 03540, Alicante (Alicante)
Contact with the Data Protection Officer: dpo@ivf-life-group.com
DATA CONTROLLER: Instituto Vasco de Fertilidad (hereinafter IVF-Life)
CIF: B95575874
Postal Address: Avenida de Tolosa, 71-73, 20018 Donostia / San Sebastián (Spain)
Contact with the Data Protection Officer: dpo@ivf-life-group.com
DATA CONTROLLER: IVF Spain Madrid (hereinafter IVF-Life)
CIF: B 85138113
Postal Address: C/ de Manuel de Falla, 6-8, 28036 Madrid (Spain)
Contact with the Data Protection Officer: dpo@ivf-life-group.com
WHAT TYPE OF DATA DO WE PROCESS?
Depending on the products, services, or functionalities that you wish to enjoy, we may need to process different types of data. In general, this data will be, depending on the case, the following:
- Your identification data: for example: name, surname, language, country from which you interact with us, contact details, etc.
- Connection, geolocation and navigation data.
- Commercial information if you are subscribed to our newsletter.
- Data about your tastes and preferences.
WHAT IS THE ORIGIN OF THE DATA?
The use of certain services or requests addressed to IVF-LIFE are subject to the prior completion of the corresponding form. All the information provided by the User through the forms on the Portal for the above purposes or any other must be truthful.
To this end, the User guarantees the authenticity of all the data provided and will keep the information provided to IVF-LIFE perfectly up to date so that it corresponds at all times to the User's real situation. In any case, the User will be solely responsible for any false or inaccurate statements made and for any damage caused to IVF-LIFE or third parties because of the information provided.
By clicking on the "send" button on the corresponding form, the User expressly consents to his/her data being used to send professional communications about his/her query by e-mail or by any other means.
However, the User may revoke the consent given and oppose the sending of such communications in each of the communications received or by sending them to the address indicated in this legal notice and enabled for this purpose. Likewise, in each of the communications sent, the procedure for opposing the sending of new professional communications shall be expressly indicated.
Users who provide personal data of other natural persons are obliged to comply, in relation to said data, with all obligations deriving from the data protection regulations in force, and in particular the duty to inform and obtain the consent of the owner of the personal data.
When we request your personal data to provide access to certain website functionalities, we will mark the required fields to ensure the service can be delivered.
Please note that if you choose not to provide us with this data, you may not be able to complete your registration as a user or you may not be able to enjoy those services or functionalities.
For the processing of data, IVF-LIFE adopts the security levels required by current European and national legislation on the Protection of Personal Data. Notwithstanding the above, technical security in a medium such as the Internet is not impregnable and there may be leaks due to the malicious actions of third parties.
Our services are aimed at people of legal age, in the event that some of our services are specifically aimed at minors, IVF-LIFE will request the consent of parents or guardians for the collection of personal data or, where appropriate, for the automated processing of data as set out in current legislation. If the User is a minor, they are required to have the prior consent of their parents or guardians before proceeding to the inclusion of their personal data in the forms on the Website.
Initially, your personal data are provided directly by you, but in certain cases they may originate from centres, referring doctors and public health systems with which there is collaboration.
FOR WHAT PURPOSES DO WE PROCESS YOUR PERSONAL DATA?
Depending on how you interact with our website, we will process your personal data for the following purposes:
To deal with requests or requests that you make through the different means incorporated into our website.
We only process the personal data that is strictly necessary to manage or resolve your request or application.
For marketing purposes
To the extent that you subscribe to our newsletter, your personal data will be used for the periodic sending of company newsletters.
You should remember that you can unsubscribe from the newsletter, at any time and free of charge, by contacting us via the e-mail address of the data controller or by following the instructions that we will provide you with in each of our communications.
For the management of social networks
If you follow us or contact us through the different social networks in which we are present, we will process the data that you provide to us through these for the sole purpose of responding to your messages or comments and managing our contact list.
Usability and quality analysis to improve our services (cookies).
If you access our platform, we inform you that we will process your browsing data for analytical and statistical purposes, i.e. to understand how users interact with our platform and thus be able to make improvements to it. Likewise, we sometimes carry out quality actions and surveys aimed at finding out the degree of satisfaction of our customers and users and detecting those areas in which we can improve.
WHAT IS THE LEGAL BASIS FOR PROCESSING YOUR DATA?
The legal basis that allows us to process your personal data also depends on the purpose for which we process them, so we will find different legal bases under the following purposes:
Attention to requests for information.
The legal basis for the processing of your data is the informed consent to respond to queries raised through the website, forms and other means provided, which implies the prior reading and acceptance of these conditions by the interested party.
Marketing
The legitimate basis for processing your data for marketing purposes is the consent you provide.
Social networking
The basis of legitimacy is the informed consent to respond to queries raised through the social network, as well as the time when you follow us and want to be part of our contact list.
Usability and quality analysis (cookies)
User consent to the use of cookies.
HOW LONG WILL WE KEEP YOUR DATA?
Request for information. We will process your data for as long as it is necessary to deal with your request or request and thereafter 1 year.
Marketing
We will process your data until you unsubscribe or cancel your subscription to the newsletter.
Social media
We will process your data for as long as it is necessary to deal with your request and for as long as you are a follower of our profile.
WILL WE SHARE YOUR DATA WITH THIRD PARTIES?
Personal data will not be transferred or communicated to third parties, except: legal obligation, we obtain your express consent, or we understand that there is a legitimate interest on our part, which will be duly communicated to you.
However, we inform you that we are present in the following social networks: Facebook, LinkedIn, Instagram and YouTube, to keep our followers informed regarding the company's news and services.
You can access these social networks voluntarily and through the links available on the website itself or by accessing directly and on your own from your browser or installed app.
You should know that this website is not responsible for the use of the data that these social networks may make. However, when these data are generated in the social network and derive from an interaction with our website, we will not be held responsible for the use of such data.
In order to consent to our transfer from this website and the processing of your data, you should carefully read the privacy policy of the social network you wish to access:
Facebook: Facebook Privacy Policy
Instagram: Instagram Privacy Policy
LinkedIn: Linkedin Privacy Policy
YouTube: Youtube Privacy Policy
Spotify: Spotify Privacy Policy
In this way, before clicking on the logos of the SS. RR. present on our website, you can inform yourself and make a redirection with prior knowledge of the processing of your data and on a voluntary basis.
Other technological services:
- WhatsApp: WhatsApp Privacy Policy
- Companies of the "IVF LIFE Group" on the legal basis of consent or legitimate interest: Instituto Vasco de Fertilidad S.L.U., with NIF B95575874 and address at Avda Tolosa, 71-73 Donostia (Gipuzkoa), and IVF Spain Madrid S.L., with NIF B85138113 and address at Calle Manuel de Falla, 6-8, 28036 Madrid.
WHAT ARE YOUR RIGHTS WHEN YOU PROVIDE US WITH YOUR DATA?
We undertake to respect the confidentiality of your personal data and to guarantee you the exercise of your rights.
You may exercise them free of charge by sending us an e-mail to our address above, simply by providing proof of identity, the reason for your request and the right you wish to exercise.
If we consider it necessary in order to identify you, we may ask you for a copy of a document proving your identity. In particular, regardless of the purpose or the legal basis on which we process your data, you have the right to:
Ask us for access to the data we hold about you.
Ask us to rectify the data we already hold about you. Please note that by actively providing us with your personal information in any way, you warrant that it is true and accurate and you undertake to notify us of any changes or modifications to it.
Ask us to delete your data to the extent that they are no longer necessary for the purpose for which we need to process them as we have previously informed you, or to the extent that we no longer have the legitimacy to do so.
Ask us to restrict the processing of your data, which means that in certain cases you may ask us to temporarily stop processing the data or to keep it longer than necessary when you may need it. If you have given us your consent to process your data for any purpose, you also have the right to withdraw your consent at any time.
To receive the personal data concerning you that you have provided to us in a structured, commonly used and machine-readable form and to transfer it to another data controller.
Moreover, where the processing of your data is based on our legitimate interest, you also have the right to object to the processing of your data.
Finally, we inform you of your right to lodge a complaint with the relevant data protection supervisory authority, with the Spanish Data Protection Agency.
CHANGES TO THE PRIVACY POLICY
We may change the information contained in this Privacy Policy from time to time. If we do so, we will notify you by various means through the Platform, or we will notify you at your email address when the change in question is significant to your privacy, so that you can review the changes, assess them and, where appropriate, object to or unsubscribe from any service or functionality.
INFORMATION ABOUT COOKIES
We use cookies and similar devices to facilitate your navigation on the Platform, to know how you interact with us and, in certain cases, to be able to show you advertising based on your browsing habits. Please read our Cookie Policy to learn more about the cookies and similar devices we use, their purpose and other information of interest.
