We are independent & ad-supported. We may earn a commission for purchases made through our links.

Advertiser Disclosure

Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.

How We Make Money

We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently from our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Morula?

Mary McMahon
Updated Mar 03, 2024
Our promise to you
The Health Board is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At The Health Board, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A morula is one of the earliest stages in embryonic development, occurring before the embryo has implanted but after it is fertilized. This stage is usually reached at about four to five days after fertilization, and it is followed by the development of the blastula, a cluster of cells surrounding a fluid-filled cavity. The morula is an important state of development, and it can be easily identified on a high power microscope used to monitor embryonic development.

Embryonic development starts with fertilization to create a zygote. The zygote starts to replicate and divide, still staying within the confines of the zona pellucida, the membrane that surrounds the outside of the egg. When around 12 to 30 cells have developed, the growing embryo becomes a morula. The cells have a slightly blurred appearance and look as though they are running together. They are also very small, because they are still inside the zona pellucida. Thus the number of cells increases, but the overall size stays the same.

Once at the morula stage, the cells begin to differentiate and arrange themselves into the blastula shape. This also marks the beginning of the disintegration of the zona pellucida, allowing the embryo to grow and implant, connecting the embryo with the uterine wall so that the placenta can develop. These are all critical landmarks in embryonic development and each landmark also represents a stage where development can go wrong or stop, sometimes with no apparent cause.

Viewed under magnification, this tight ball of cells resembles the fruit of the mulberry tree. This is referenced in the name "morula," Latin for "mulberry." The number of cells involved can change because, as the cells start dividing, they can divide at different rates. Developing embryos do not follow an exponential progression of two, four, eight, 16, and 32 cells, in other words; at any given time the number of cells in the embryo can vary.

When people are treated with in vitro fertilization for infertility problems, physicians aim to transfer the embryos after the morula stage so that they can implant inside the uterus. If the developing embryo is still a morula after five days, this raises concerns that it may not develop any further and is no longer viable, although it may be perfectly healthy and just a little slower than usual. Some physicians like to wait to transfer until they are confident that cell division and development are still occurring, while others may go ahead and transfer a morula.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By SailorJerry — On Jun 27, 2011

@ElizaBennett - My understanding is that identical twin formation would happen at the blastocyst stage. Some researchers who study embryonic stem cells, therapeutic cloning, and that sort of thing are comfortable with working with embryos at the blastocyst stage precisely because it's still so uncommitted. It could become two people, it has no top or bottom, etc.

But the next stage, the gastrula, is after primitive streak formation (which will eventually become the backbone). Then you can definitely have only one individual and it is starting to develop its form. Although this is still a super-early stage when a lot can still go wrong.

By ElizaBennett — On Jun 25, 2011

Can a morula still divide in two and become identical twins? Can a blastocyst? I know this is a stage when no test that exists could tell if you're pregnant, because your body doesn't even know until implantation I don't think.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.

The Health Board, in your inbox

Our latest articles, guides, and more, delivered daily.