Assisted Reproductive Technology (ART) often requires controlled ovarian stimulation to encourage the development of multiple eggs. This process carries the potential for a complication known as Ovarian Hyperstimulation Syndrome (OHSS). OHSS is a systemic response to excessive hormonal stimulation, and its occurrence often raises concerns about the quality of the retrieved eggs. This article explores the current understanding of OHSS and addresses whether this condition impairs the intrinsic quality of eggs used for in vitro fertilization (IVF).
Defining Ovarian Hyperstimulation Syndrome
Ovarian Hyperstimulation Syndrome (OHSS) is an exaggerated response of the ovaries to injectable hormone medications used in IVF protocols. The condition is often triggered by the final maturation injection, typically human chorionic gonadotropin (hCG). This hormone causes blood vessels near the ovaries to become porous, leading to a shift of fluid from the bloodstream into the abdominal cavity, which causes the ovaries to swell and become painful.
This fluid shift causes the wide range of symptoms that classify the syndrome’s severity. Mild to moderate symptoms include abdominal bloating, nausea, vomiting, diarrhea, and mild weight gain. Severe cases involve significant fluid accumulation, rapid weight gain, severe abdominal pain, and potentially life-threatening complications like blood clots or difficulty breathing. Since the body naturally produces hCG during pregnancy, OHSS symptoms can sometimes worsen and persist for several days or weeks in a successful cycle.
The Direct Impact on Egg Quality
The medical consensus is that the physical and inflammatory effects of OHSS do not directly impair the intrinsic quality of the retrieved oocytes. Eggs that were mature and healthy before the onset of the syndrome remain viable for fertilization and subsequent development. Studies focusing on egg quality, such as genetic integrity or cellular health, generally do not show a negative impact directly attributable to the OHSS condition.
Any perceived reduction in egg quality is usually related to underlying conditions that predispose a patient to OHSS, such as Polycystic Ovary Syndrome (PCOS), or the nature of the high-response cycle itself. The inflammation and fluid shifts associated with OHSS occur after the eggs are already mature or have been retrieved. This means the gametes are largely protected from the syndrome’s systemic effects. The overall number of viable embryos produced is generally not diminished by an OHSS diagnosis.
How High Response Cycles Affect Embryo Viability
While OHSS does not directly damage mature eggs, the high-response cycle that leads to OHSS introduces a nuance regarding embryo viability. High-response cycles stimulate a large number of follicles, which is associated with retrieving a greater proportion of immature eggs. This results in a lower oocyte maturation rate compared to normal response cycles.
The immaturity of these eggs affects the overall number of viable embryos, as they cannot be fertilized or may exhibit impaired development. However, the mature eggs retrieved from these high-response cycles possess a similar fertilization potential to those from normal cycles. Although a high yield may include a higher percentage of non-viable oocytes, the mature eggs that form embryos tend to have comparable implantation potential and live birth rates.
Clinical Strategies When OHSS Risk is High
When a patient has a high risk for OHSS, the clinical strategy prioritizes patient safety while preserving the viability of retrieved eggs. One common strategy replaces the standard hCG final maturation injection, which is strongly linked to causing OHSS, with a Gonadotropin-Releasing Hormone (GnRH) agonist trigger. The GnRH agonist trigger induces final maturation but causes a rapid, short-lived hormonal surge that significantly reduces the risk of severe OHSS.
This approach is coupled with a “freeze-all” strategy, where all resulting eggs or embryos are cryopreserved instead of performing a fresh embryo transfer. Freezing allows the patient’s body to recover fully from the intense stimulation and any mild OHSS symptoms before a subsequent frozen embryo transfer (FET). This segmentation of the IVF cycle mitigates the risk of OHSS without compromising the cumulative pregnancy rate, confirming the eggs and embryos remain viable for future use.