Egg retrieval is a procedure within the In Vitro Fertilization (IVF) process where mature eggs are collected from the ovaries to be fertilized in a laboratory. The phase leading up to this retrieval involves ovarian stimulation, using injectable medications to encourage the ovaries to produce many mature follicles instead of the single one that develops naturally. A person can become pregnant before egg retrieval, and this possibility is a known, though rare, risk that fertility clinics actively work to prevent. This spontaneous conception occurs if an egg is released prematurely and sperm is present in the reproductive tract.
The Mechanism of Risk During Ovarian Stimulation
The stimulation phase of an IVF cycle intentionally creates an environment highly conducive to conception. Normally, only one dominant follicle matures, and the body prevents its premature release. During ovarian stimulation, high doses of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) or similar medications are administered to develop multiple follicles simultaneously.
These medications cause the ovaries to become hyper-responsive, growing many follicles that produce high levels of estradiol. In a non-medicated cycle, estradiol signals the brain to trigger an LH surge, which is the natural signal for spontaneous ovulation and egg release. If spontaneous ovulation occurs during a stimulated cycle, and recent intercourse has taken place, natural conception can occur, compromising the IVF cycle.
The risk is compounded because sperm can survive in the reproductive tract for several days, allowing an unexpectedly released egg to be fertilized. Clinics must balance stimulating egg growth while suppressing the body’s natural impulse to prematurely ovulate. The presence of numerous enlarged follicles also increases the risk of ovarian torsion, requiring close medical management.
Medications Used to Control Ovulation Timing
To counteract the body’s drive to ovulate prematurely, specific suppression drugs are introduced to prevent the Luteinizing Hormone (LH) surge that triggers ovulation. Gonadotropin-releasing hormone (GnRH) agonists (e.g., leuprolide) or GnRH antagonists (e.g., cetrorelix or ganirelix) are the primary tools used for this purpose.
GnRH antagonists work by binding to receptors in the pituitary gland, quickly blocking the release of LH and Follicle-Stimulating Hormone (FSH). This action prevents the spontaneous LH surge and maintains control over the timing of egg release. Antagonists are often started several days into the stimulation phase once follicles reach a specific size, typically around 12 millimeters in mean diameter.
In contrast, GnRH agonists initially cause a massive surge of LH and FSH, but then desensitize and suppress the pituitary gland, shutting down natural hormonal regulation. Both agonists and antagonists prevent premature ovulation, ensuring eggs remain in the ovaries until retrieval. The final step is the “trigger shot,” a dose of human chorionic gonadotropin (hCG) or a GnRH agonist given approximately 36 hours before the scheduled retrieval to induce final egg maturation.
Required Precautions Before Egg Retrieval
To eliminate the chance of spontaneous pregnancy, fertility clinics implement strict protocols during the ovarian stimulation phase. The most direct precaution is mandatory abstinence from unprotected intercourse, beginning when stimulation drugs are started or once follicles reach a certain size. This ensures that no viable sperm are present in the reproductive tract if spontaneous ovulation occurs despite the suppression medications.
Some clinics may permit barrier methods, though many advise complete abstinence to remove all risk. Refraining from intercourse also reduces the risk of discomfort or complications, as the ovaries are temporarily enlarged due to the multiple growing follicles. This enlargement can make intercourse painful and potentially increase the risk of ovarian torsion.
Close medical monitoring is another precaution to ensure the suppression medications are working and the timing of retrieval is accurate. This involves frequent transvaginal ultrasounds to measure follicle size and number, and regular blood tests to check hormone levels, particularly estradiol and progesterone. Monitoring allows the medical team to detect signs of an impending natural LH surge or premature ovulation and make immediate adjustments to the medication protocol.