The spindle apparatus directly influences the genetic quality of embryos

Did you know that inside the egg and embryo there is a microscopic “machine” that can decide whether the future baby will have a more stable genetic foundation or not? That machine is the spindle apparatus and, in the context of a surrogacy process , can play a key role in the quality of the embryo that will be transferred. But what exactly is it, how does it work, and why does it matter so much? Let’s discover it step by step.

What is the spindle apparatus?

The spindle apparatus is a cellular structure composed of microtubules (thin threads of protein called tubulin) and other associated proteins that forms when a cell divides. Its main function is to organize and separate the chromosomes correctly so that each daughter cell receives the exact genetic information.

In human eggs and embryos, this machinery is very sensitive: a failure in its formation or functioning can cause chromosomes to not separate properly, which can lead to genetic errors, chromosomal abnormalities (such as embryo failure, aneuploidy) or compromised embryonic development.

Why does it matter in a surrogacy process?

Surrogacy is a process in which a woman—the surrogate mother — carries a pregnancy for another person or couple (the intended parents). In most cases, an embryo created through in vitro fertilization (IVF) is used, which is then transferred to the surrogate mother’s uterus.

In this context, the higher the “genetic quality” of the embryo — that is, the lower the risk of chromosomal abnormalities and the greater the potential for implantation and development — the greater the likelihood that the process will lead to a successful and healthy pregnancy. This genetic quality is influenced by multiple factors (the age of the egg donor, sperm quality, IVF laboratory, and the techniques used) and also by the “conditions of the egg and embryo” from the beginning, including the functioning of its spindle apparatus.

If the spindle apparatus doesn’t function properly, errors in embryo cell division can occur, resulting in embryos with chromosomal abnormalities or altered genetic structure. Since it’s crucial in surrogacy to ensure the embryo has the maximum potential for success, understanding this microscopic aspect can make all the difference.

How does the spindle apparatus influence the genetic quality of the embryo?

Formation and function of the spindle in the egg and embryo

Before fertilization, the egg must undergo meiosis (two divisions that reduce the number of chromosomes by half). During these divisions, the spindle apparatus is responsible for moving the chromosomes in an orderly manner. If something goes wrong, the egg can end up with an incorrect number of chromosomes, which affects the embryo from the beginning.

After fertilization and embryo formation, the first mitotic divisions also require a stable, properly formed spindle so that each new cell contains the complete genetic information. Studies have found that the shape of the spindle in the first mitosis of human embryos is associated with nuclear abnormalities, which affect future embryonic development.

Scientific evidence of its relationship with embryonic quality

• A study found that in human embryos, the shape of the first spindle (measured as the “ aspect ratio”) is correlated with multinucleation (i.e., more than one nucleus in a cell) and fragmentation, which reduces embryonic quality.
• Another study on mouse eggs concluded that the volume, width, and shape of the spindle are associated with the egg’s ability to reach blastocyst . That is, a better spindle → a greater likelihood of development.
• In humans, detecting the meiotic spindle (before sperm injection) was associated with higher fertilization rates and better embryos.
• Cells that have damage to the spindle or do not form it well can activate the spindle assembly checkpoint, but if they fail to correct it, they can continue dividing with errors, which generates aneuploidy (embryo with extra or missing chromosomes).

Practical consequence: genetic quality of the embryo

Therefore, proper formation and functioning of the spindle apparatus can be seen as one of the microscopic pillars that contribute to the embryo having:

• A correct number of chromosomes (euploidy)
• Cells without fragmentation or multinucleation in early stages
• Good potential for implementation
• Decreased risk of miscarriage or failure in early stages

In the context of surrogacy, where the goal is to maximize probabilities and minimize risks, this factor may not be visible to the naked eye, but it is relevant when selecting eggs, working in the IVF laboratory, and ensuring that the embryo is within the best possible parameters before transfer.

What can a surrogacy clinic do to optimize this aspect?

Although the spindle apparatus is something that occurs at the cellular level and is often not directly visible in all embryos, there are good practices that can increase the chances of everything being aligned “correctly”:

1. Choosing good quality eggs : The donor’s age, medical history, and ovarian health all influence whether the eggs have good potential and whether their spindle apparatus is more reliable.
2. High-quality laboratory and advanced technology : The use of high-resolution microscopy, systems that allow visualization of the spindle (for example, in eggs before ICSI) can allow selecting those with the best parameters. Studies indicate that the presence of a visible spindle is associated with better results.
3. Optimizing oocyte maturation : In properly matured eggs (in vivo or undergoing adequate maturation), the spindle tends to have a better shape. According to mice, eggs with excellent spindles correlate with development toward blastocysts.
4. Minimize egg handling and stress : Laboratory factors, freezing/thawing, can affect spindle integrity or functionality.
5. Embryonic monitoring and selection : Although it is not always possible to see the embryonic spindle, laboratories can observe parameters such as fragmentation, multinucleation , and proper development, which may indirectly reflect that the spindle did its job well.

Limitations and what we don’t know yet

As with any emerging scientific topic, there are also some “buts” that are worth knowing for a complete explanation.

• Although there is a correlation between good spindle function and better results, there is no absolute guarantee: an egg with a good spindle function may still have other genetic errors that are not detected at that stage.
• Much of the research has been on egg or animal models, or partly on research embryos, rather than on surrogacy embryos specifically.
• Visualization of the spindle in human embryos is complicated, and not all laboratories can do it routinely.
• The decision to transfer in surrogacy does not depend solely on the spindle: sperm quality, embryo, health of the surrogate, timing, etc., all play a role.
• There are external factors (age of the mother/donor, culture medium, embryo manipulation) that can affect the spindle and other complementary cellular mechanisms.

Therefore, although the spindle apparatus is an important factor in the genetic quality of the embryo, it should be viewed as just another factor in a chain of care, selection, and good protocol.

What does this mean for people considering surrogacy?

If you are considering surrogacy, or are in the process of doing so with an agency like Gestlife, here are some specific implications:

• When you inquire about the IVF laboratory, you may want to ask about the methods they use for egg and embryo evaluation, and whether they have advanced microscopy/selection criteria that include spindle evaluation.
• Understanding that embryo quality depends not only on the number of embryos but also on their “internal potential,” and one of these potentials is related to the spindle.
• Know that, although the “spindle apparatus” is not explicitly mentioned in all reports, the best centers do have refined selection protocols that indirectly consider it.
• Don’t focus solely on this factor: it’s one, but the overall surrogacy process includes many steps (synchronization, preparation of the surrogate, transfer, follow-up) that are also extremely important.
• Rest easy knowing that professional surrogacy agencies are familiar with these advancements and can guide you on best laboratory practices, embryo selection, egg and sperm donors, and more.

Conclusion

Science demonstrates with growing evidence that the spindle apparatus —the tiny structure that organizes chromosomes within eggs and embryos—plays a decisive role in the genetic quality of the embryo . In the context of surrogacy , where the goal is to achieve a healthy and safe pregnancy, this microscopic element represents a key factor in the complex reproductive process.

Simply put, a properly formed spindle promotes proper chromosome alignment , which translates into more genetically stable embryos and higher success rates . However, the final result depends on perfect synchrony between all components of the process: from the quality of the gametes and laboratory conditions to the preparation of the surrogate mother and embryo transfer.

At Gestlife we have specialized medical teams that ensure that every step—from egg selection to embryo implantation—is carried out with the highest standards of quality and safety.

Frequently Asked Questions (FAQs)

What does it mean to “assess the spindle” in an egg or embryo?

Assessing the spindle means using special microscopy to visualize the microtubule structure in the egg (or in the very early embryo) and verify that it is well formed, correctly positioned, and has the proper shape. Studies indicate that eggs with a visible spindle tend to have better fertilization rates and higher-quality embryos.

Can I specifically request spindle evaluation at an IVF surrogacy center?

Yes, you can ask about it. Some fertility centers offer polarized microscopy or spindle imaging technologies before sperm injection into eggs (ICSI). This is a good additional indicator of egg quality, although it is not the only one.

If the spindle isn’t perfect, does that mean the embryo is doomed to failure?

Not necessarily. A spindle that isn’t the “ideal” shape can increase the risk of errors, but it doesn’t guarantee failure. There are other cellular “correction” mechanisms, and the embryo can still develop. However, the probability of success may be lower. IVF teams consider this as another evaluation factor.

Is this spindle issue more relevant to surrogacy than to conventional IVF?

In many ways, it’s equally relevant to both. However, in surrogacy, where donor selection, egg donation, transfer to surrogate mothers, etc., involves maximizing embryo quality is even more important to optimize results and minimize risks. That’s why it’s worth paying attention to details like the spindle, in addition to other reproductive criteria.

What can I do to ensure that my eggs/all factors have better “spindles” or quality?

Some recommendations: choose a young, healthy egg donor, ensure the IVF lab is experienced and uses high-quality technology, minimize egg handling time, optimize culture conditions, maintain good overall health (nutrition, antioxidants, avoiding toxins), etc. While there’s no absolute guarantee, all of these steps increase the odds.