Skip to content 
Pregnancy is the first thing that comes to mind for most people when they hear about surrogacy: a woman carrying another family’s child. However, what many don’t realize is that the true beginning of this story occurs long before the presence of an embryo.
It all starts in a laboratory and at a doctor’s appointment. And at that moment, an essential process unfolds that is rarely described in detail: ovarian stimulation.
You probably have many questions if you’re researching surrogacy:
Where do the eggs come from?
Who provides them?
How are they obtained?
And what exactly is the role of science in all of this?
Answering these questions not only helps us understand how this reproductive method works, but also allows us to understand why, thanks to assisted reproductive technologies, hundreds of thousands of families worldwide have been able to conceive.
However, before detailing egg retrieval, it’s important to understand what surrogacy is and how it relates to the entire medical process.
The real starting point is ovarian stimulation
In a natural menstrual cycle, the female body typically releases one egg per month. However, in fertility treatments such as in vitro fertilization (IVF), which is essential for surrogacy, doctors try to obtain multiple eggs in a single cycle.
Ovarian stimulation is used to achieve this. This hormonal treatment aims to stimulate the ovaries to produce several mature eggs instead of just one.
According to reproductive specialist Eric S. Surrey MD, author of a review published in Fertility and Sterility.
“Stimulating the ovaries to produce more than one mature oocyte and thus improving the chances of a live birth.”
This means that ovarian stimulation is a fundamental part of assisted reproductive treatments. Its goal is to encourage the ovaries to produce multiple mature oocytes in a single cycle, which increases the chances of achieving pregnancy and, ultimately, a live birth.
It was long believed that the more oocytes retrieved, the greater the likelihood of success. However, recent studies indicate that not only is the quantity of oocytes retrieved important, but also their quality. Some studies suggest that ovarian stimulation may impact the development of the endometrium; this could affect embryo implantation.
How ovarian stimulation works and how eggs are obtained
During ovarian stimulation, the woman providing the eggs—whether the intended mother or a donor—receives treatment with hormonal medications that help stimulate the ovaries. The goal is for several eggs to develop simultaneously, instead of just one maturing as in a natural cycle.
These hormones work by mimicking or reinforcing the body’s own natural signals, allowing several ovarian follicles to grow simultaneously. Follicles are small structures within the ovaries where eggs develop.
Throughout this process, the medical team closely monitors the pregnancy using ultrasounds and hormone tests. These checks allow them to observe the growth of the follicles and determine the precise moment when the eggs are ready.
“trigger” is administered. “shot “, which causes the final maturation of the eggs and prepares the body for the next step.
And that’s when one of the most important phases of the process arrives: the egg retrieval.
Egg retrieval, also known as egg Egg retrieval is the medical procedure by which mature eggs are collected from the ovaries for later use in the laboratory. This step is usually performed approximately 36 hours after the last hormonal injection, when the eggs have reached their optimal point of maturation.
During the procedure, the doctor uses a thin needle guided by ultrasound to gently aspirate the follicles and collect the eggs inside them.
It is a minimally invasive procedure, usually performed under light sedation to ensure the patient is comfortable and relaxed. It is also relatively quick, typically lasting between 20 and 30 minutes.
Once retrieved, the eggs are immediately transferred to the embryology laboratory. There, the next stage of the process begins: fertilization, where specialists will work to create embryos that can later be transferred to the uterus.
What happens after egg retrieval
After obtaining the eggs, the assisted reproduction specialists analyze each one to evaluate its maturity and quality.
Mature eggs are fertilized in the laboratory with sperm through in vitro fertilization (IVF) or through a technique called ICSI ( intracytoplasmic sperm injection).
The goal is to create viable embryos that can develop properly.
In the following days, embryologists carefully observe the development of the embryos to select those with the greatest implantation potential.
Finally, one of those embryos will be transferred to the pregnant woman’s uterus.
And it is at that moment —only then— that the pregnancy within surrogacy truly begins.
Why is ovarian stimulation so important and who provides the eggs in surrogacy?
The importance of ovarian stimulation in assisted reproduction treatments is easily understood: its goal is to increase the chances of achieving pregnancy. By stimulating the ovaries to produce multiple eggs in a single cycle, specialists have more opportunities to create viable embryos.
Dr. David Gardner, a renowned researcher in reproductive medicine, explains that having several eggs allows embryologists to work with more options and select the embryos with the greatest development potential, which increases the chances of success in fertility treatments.
Without ovarian stimulation, doctors would have to work with only one egg per menstrual cycle, which is what happens naturally in a woman’s body. This would severely limit the options, since not all eggs are successfully fertilized, nor do all embryos develop normally.
Having multiple eggs completely changes the scenario. It allows for the creation of different embryos, analysis of which ones have the best characteristics, and selection of the most suitable for transfer. Furthermore, when more embryos are generated than are used in a single attempt, they can be frozen for future treatments, avoiding the need to repeat the entire process from the beginning.
Thanks to this approach, in vitro fertilization techniques have significantly improved their results in recent decades.
When we talk about surrogacy, a very common question also arises: where do the eggs used to create the embryo come from?
The answer depends on each situation and the medical characteristics of the intended parents. In some cases, the intended mother can provide her own eggs, allowing for a direct genetic link with the baby. In other cases, donor eggs are used, especially when the intended mother cannot produce viable eggs or prefers this option.
There is also a third possibility, although less frequent: using donated embryos, which have already been created previously through in vitro fertilization.
When donor eggs are used, the entire ovarian stimulation process is performed on the donor, not the intended mother. After egg retrieval, the procedure continues with the same steps as in any assisted reproductive technology treatment: the eggs are fertilized in the laboratory, embryos are created, and finally, one of them is transferred to the surrogate’s uterus to begin the pregnancy.
What science has learned about ovarian stimulation
Ovarian stimulation has been part of fertility treatments for over four decades. During this time, reproductive medicine has advanced enormously, developing various hormonal protocols that aim to improve outcomes while simultaneously reducing potential risks for patients.
Even so, research in this field continues to evolve. Researchers point out that there is still a scientific debate about which stimulation protocols are most effective in each clinical situation, which has driven numerous studies and advances in assisted reproduction in recent years.
Meanwhile, research shows that the controlled use of hormones allows for the retrieval of multiple eggs in a single cycle. This advance has brought about a significant change in fertility treatments, as it increases the chances of creating viable embryos and, therefore, achieving pregnancy.
Thanks to all these advances, today specialists can adapt treatments to the characteristics of each patient, designing more personalized protocols tailored to each case.
When people talk about surrogacy, many tend to think only of the pregnancy and the surrogate mother. However, the truth is that the process begins much earlier and is the result of the collaborative work of different areas of medicine: endocrinology, genetics, embryology, and assisted reproduction.
Ovarian stimulation, egg retrieval, fertilization in the laboratory, and embryo development are all part of a carefully coordinated chain of medical steps. Each stage is important and depends on the previous one for everything to function correctly.
Only when this entire process is successful can the pregnancy begin. And for many families, that moment represents much more than a medical treatment: it is the culmination of years of hope and the beginning of the journey toward the possibility of having a child.
The future of ovarian stimulation in assisted reproduction
Reproductive medicine is advancing rapidly. In recent years, researchers have been exploring new tools and technologies—including artificial intelligence —to improve fertility treatments. The goal is to optimize ovarian stimulation protocols and more accurately predict the best time for egg retrieval.
These advances could allow treatments to become increasingly personalized, better adapting to the characteristics of each patient and increasing the chances of success in processes such as surrogacy.
If we think about it, it’s astonishing: what seemed like science fiction just forty years ago is now part of modern medicine. And each new discovery brings many people a little closer to something as important as being able to start a family.
To truly understand how surrogacy works, it’s necessary to look beyond the pregnancy itself. Behind it lies a whole set of scientific processes that make it possible.
From ovarian stimulation to egg retrieval, through fertilization in the laboratory and embryo development, each step is part of a carefully coordinated medical process. It’s a kind of intricate system where each phase depends on the previous one for everything to function correctly.
Thanks to this combination of science, technology, and medical expertise, millions of people around the world have been able to fulfill their dream of becoming parents.
Surrogacy story is unique, they all share something in common: they actually begin long before pregnancy. They begin with a microscopic cell, a specialized medical team, and a carefully designed scientific process to create a new life.
