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The medical steps that occur before pregnancy in surrogacy
For many people, the word surrogacy immediately evokes the image of pregnancy: a woman carrying a child on behalf of another individual or family. Yet the true beginning of this journey occurs long before a pregnancy is established — indeed, before an embryo even exists.
In reality, the process commences in a fertility clinic and within specialised embryology laboratories. At this stage an essential medical procedure unfolds, one that is rarely discussed in depth outside clinical contexts: ovarian stimulation.
Individuals exploring surrogacy often find themselves asking several important questions.
Where do the eggs originate? Who provides them? How are they obtained? And what role does medical science play in facilitating this process?
Addressing these questions not only clarifies how surrogacy operates as a reproductive pathway, but also highlights the remarkable advances made possible through assisted reproductive technologies (ART). Thanks to these innovations, hundreds of thousands of families across the globe have been able to conceive when natural conception was not possible.
Before discussing egg retrieval, however, it is important to understand the broader medical framework of surrogacy and the biological processes that precede embryo creation. The journey begins with ovarian stimulation.
The real starting point: ovarian stimulation
Under natural physiological conditions, a typical menstrual cycle results in the release of a single oocyte from the ovary each month. This process, known as ovulation, is sufficient for natural conception but presents limitations within the context of assisted reproduction.
In fertility treatments such as in vitro fertilisation (IVF) —a fundamental component of most surrogacy arrangements— clinicians aim to retrieve multiple oocytes within a single cycle in order to increase the likelihood of generating viable embryos.
To achieve this, patients undergo controlled ovarian stimulation (COS). This treatment involves the administration of carefully calibrated hormonal medications designed to stimulate the ovaries to produce several mature oocytes rather than a single egg.
Reproductive endocrinologist Dr Eric S. Surrey, in a review published in the journal Fertility and Sterility, explains that the purpose of ovarian stimulation is to induce the development of multiple mature oocytes in order to enhance the probability of achieving a live birth. Source: Science Direct.
For many years it was widely assumed that retrieving a greater number of oocytes would necessarily translate into higher pregnancy rates. However, contemporary research suggests that oocyte quality may be as important as quantity.
Some studies have also indicated that ovarian stimulation may influence the endometrial environment, potentially affecting embryo implantation. These findings have prompted ongoing research aimed at refining stimulation protocols and optimising reproductive outcomes.
How ovarian stimulation works and how eggs are obtained
During ovarian stimulation, the woman providing the oocytes —either the intended mother or an egg donor— receives a course of hormonal medications designed to activate the ovaries. Rather than allowing a single egg to mature naturally, the treatment encourages the simultaneous development of multiple ovarian follicles.
These hormones essentially replicate and enhance the body’s natural endocrine signals, promoting the growth of several follicles, which are microscopic fluid-filled structures within the ovaries where oocytes mature. Throughout this phase, fertility specialists monitor the patient closely using transvaginal ultrasound scans and hormonal blood tests. These assessments enable clinicians to track follicular development and determine the precise moment when the oocytes have reached optimal maturity.
Once the follicles reach an appropriate size, a final hormonal injection —commonly referred to as a trigger injection— is administered. This medication initiates the final maturation of the oocytes and prepares them for retrieval. At this point the next crucial stage begins: egg retrieval.
Egg retrieval, also known clinically as oocyte retrieval, is the procedure through which mature eggs are collected from the ovaries for use in the embryology laboratory. This procedure is typically performed approximately 36 hours after the trigger injection, when the oocytes have reached their optimal stage of maturation.
Using ultrasound guidance, the physician inserts a fine aspiration needle through the vaginal wall in order to carefully collect the follicular fluid containing the oocytes. The procedure is considered minimally invasive and is generally performed under light intravenous sedation to ensure patient comfort. In most cases, the process lasts between twenty and thirty minutes. Immediately after retrieval, the oocytes are transferred to the embryology laboratory, where the next stage —fertilisation— takes place.
What happens after egg retrieval
Once the eggs have been retrieved, embryologists examine each oocyte carefully to assess its maturity and developmental potential. Mature oocytes are then fertilised in the laboratory using sperm through in vitro fertilisation (IVF). In certain circumstances, a specialised technique known as intracytoplasmic sperm injection (ICSI) may be employed, whereby a single sperm cell is injected directly into the egg.
The objective of this stage is to generate viable embryos capable of developing normally. Over the following days, embryologists observe embryo development under controlled laboratory conditions, evaluating which embryos demonstrate the highest implantation potential.
Ultimately, one selected embryo is transferred into the uterus of the surrogate. It is at this precise moment —and not before— that pregnancy in a surrogacy arrangement truly begins.
Why ovarian stimulation is so important and who provides the eggs in surrogacy
The importance of ovarian stimulation within assisted reproduction is relatively straightforward: it significantly enhances the probability of achieving pregnancy. By enabling the retrieval of multiple oocytes within a single cycle, clinicians gain more opportunities to create embryos and identify those with the strongest developmental potential.
Prominent reproductive scientist Professor David Gardner has emphasised that having access to multiple embryos allows embryologists to select those with the greatest likelihood of implantation, thereby improving success rates in fertility treatments. Without ovarian stimulation, physicians would typically have only a single egg available per menstrual cycle. This would considerably restrict reproductive options, as not all eggs fertilise successfully and not all embryos develop appropriately.
Retrieving multiple eggs therefore allows clinicians to generate several embryos, evaluate their quality and select the most suitable candidate for transfer. Furthermore, when additional embryos are produced, they may be cryopreserved for future attempts, eliminating the need to repeat the entire stimulation and retrieval process.
This strategy has contributed substantially to the improved success rates observed in IVF over recent decades. A further question often arises in discussions of surrogacy: where do the eggs originate? The answer varies depending on the circumstances of each case.
In some situations, the intended mother may use her own oocytes, allowing for a direct genetic connection to the child. In other cases, donor eggs are utilised — particularly when the intended mother cannot produce viable oocytes or when donor gametes are medically recommended. A third, less common option involves the use of donated embryos, which have previously been created through IVF. When donor eggs are used, the ovarian stimulation process is performed in the donor rather than the intended mother. Following egg retrieval, the clinical procedure proceeds in the same manner: fertilisation in the laboratory, embryo culture, and eventual embryo transfer to the surrogate.
What science has learned about ovarian stimulation
Ovarian stimulation has been an integral component of fertility treatment for more than forty years. Over this period, reproductive medicine has made considerable progress in developing hormonal protocols designed to optimise outcomes while minimising patient risk.
Nevertheless, scientific research in this field remains active. Investigators continue to debate which stimulation strategies provide the most favourable outcomes in different clinical scenarios. Studies have consistently demonstrated that the controlled use of reproductive hormones enables clinicians to retrieve multiple oocytes within a single cycle — an innovation that has dramatically improved the success rates of fertility treatments.
As a result of these advances, clinicians are now able to tailor treatment protocols to the specific physiological characteristics of each patient, creating highly individualised fertility treatment plans. When surrogacy is discussed in public discourse, attention often focuses primarily on the pregnancy itself. In reality, however, the process is the culmination of a complex collaboration between multiple medical disciplines, including reproductive endocrinology, genetics, embryology and assisted reproductive medicine.
Ovarian stimulation, egg retrieval, laboratory fertilisation and embryo development form a carefully coordinated sequence of medical procedures. Each stage depends upon the successful completion of the previous one. Only when these processes align successfully can a pregnancy begin.
For many families, that moment represents far more than a medical milestone — it marks the fulfilment of years of hope and perseverance.
The future of ovarian stimulation in assisted reproduction
The field of reproductive medicine continues to evolve at a remarkable pace. In recent years, researchers have begun exploring the integration of artificial intelligence and advanced data analysis in order to refine fertility treatments. These emerging technologies may help optimise ovarian stimulation protocols and improve the prediction of the ideal timing for egg retrieval.
Such innovations could allow fertility treatments to become even more precisely tailored to individual patients, further improving success rates in processes such as surrogacy. It is remarkable to consider that techniques which would have seemed like science fiction only a few decades ago are now firmly established within modern medicine. Each scientific advance brings more individuals closer to the possibility of building a family.
To truly understand surrogacy, one must look beyond pregnancy itself. Behind every successful surrogacy journey lies a sophisticated sequence of scientific procedures. From ovarian stimulation and egg retrieval to laboratory fertilisation and embryo development, each step forms part of a carefully orchestrated medical process. It is this remarkable combination of science, clinical expertise and technological innovation that has enabled millions of people worldwide to become parents.
And although every surrogacy journey is unique, they all share one defining characteristic: they begin long before pregnancy. They begin with a microscopic cell, a team of dedicated specialists, and a meticulously designed scientific process aimed at creating new life.
