A frozen embryo transfer (FET) is a procedure in in vitro fertilization (IVF) where a cryopreserved embryo is thawed and placed into a woman’s uterus. This allows individuals to attempt pregnancy without another full cycle of ovarian stimulation and egg retrieval. Patients often ask about the possibility of natural pregnancy before a scheduled FET.
The Possibility of Natural Conception
While fertility treatments aim to control the reproductive cycle, natural conception before a frozen embryo transfer is possible, though uncommon. This can occur if spontaneous ovulation takes place during the lead-up to the FET, especially in cycles where ovarian activity is not fully suppressed or in natural FET protocols. Even with medications designed to regulate the cycle, such as birth control pills or GnRH agonists, their efficacy is not always 100%, allowing for unintended natural ovulation.
In natural cycle FETs, a patient’s hormonal fluctuations are tracked, and ovulation is intentionally monitored to time the embryo transfer. A natural pregnancy could result if intercourse occurs around this time. A naturally conceived pregnancy might also occur if a previous IVF cycle was not fully cleared from the body, or if an egg was missed during a prior egg retrieval and subsequently fertilized.
Why Pregnancy Before Transfer is a Critical Concern
A natural pregnancy before a scheduled frozen embryo transfer presents several implications for both the patient and the clinic. A primary concern is the need to cancel or postpone the planned FET cycle, which can be emotionally and financially impactful for patients.
Medications used to prepare the uterine lining for FET might interact with a spontaneously conceived pregnancy. While not always harmful, managing two concurrent pregnancies—one natural and one from the potential FET—can be complex. There is also a risk of multiple pregnancy if a natural conception occurs and the FET proceeds, leading to higher risks for the birthing parent and the fetuses, including preterm birth, gestational diabetes, and preeclampsia. Clinics must ensure a clear uterine environment to avoid such complications.
Clinical Protocols to Prevent and Detect Pregnancy
Fertility clinics implement measures to prevent and detect natural pregnancy before a frozen embryo transfer. Many protocols begin with ovarian suppression, often using birth control pills or hormonal medications like leuprolide (Lupron) or GnRH antagonists. These medications quiet the ovaries and prevent spontaneous ovulation, allowing the medical team to control cycle timing. This controlled environment ensures the uterus is optimally prepared for the thawed embryo.
Throughout the FET cycle, patients undergo regular monitoring, including blood tests and ultrasound scans. Blood tests typically measure hormone levels, especially human chorionic gonadotropin (hCG), a marker for pregnancy. A baseline hCG test is often performed at the start of the cycle to confirm the absence of an existing pregnancy. Ultrasound scans assess the uterine lining’s thickness and pattern, ensuring it is receptive for embryo implantation, and confirm no dominant follicles are developing, which could indicate impending natural ovulation.
Steps to Take if Pregnancy is Suspected
If a patient suspects or confirms a natural pregnancy before their scheduled frozen embryo transfer, immediate communication with their fertility clinic is important. Patients should contact their medical team without delay to report any potential pregnancy symptoms or positive home pregnancy tests. It is important to avoid self-medicating or making assumptions.
The clinic will provide specific guidance, typically involving further testing like blood work to confirm hCG levels and potentially an ultrasound. Based on these results, the medical team will advise on next steps, which may include postponing or canceling the FET cycle to prioritize the naturally conceived pregnancy. This direct communication ensures appropriate medical management and helps navigate the situation safely.