Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy, often referred to as the “pregnancy hormone.” After an embryo transfer in In Vitro Fertilization (IVF), hCG indicates and supports a potential pregnancy. The presence of hCG signals that the embryo has implanted into the uterine lining. This hormone is essential for maintaining early pregnancy by supporting the corpus luteum to produce progesterone, which helps sustain the uterine lining.
The HCG Rise Timeline
After an embryo transfer, hCG begins to rise once the embryo implants into the uterine wall. Implantation typically occurs between 3 to 8 days following a day 5 (blastocyst) embryo transfer, and 5 to 7 days after a day 3 embryo transfer. Once implantation occurs, the developing placental cells start producing hCG, which then enters the bloodstream.
For a day 5 embryo transfer, hCG may become detectable in blood tests as early as 7 days post-transfer, though most clinics recommend testing around 9 to 14 days. With a day 3 embryo transfer, detection might occur slightly later, around 9 days post-transfer, but clinics advise waiting 12-14 days for a more reliable result.
Understanding HCG Levels
Once hCG begins to rise, specific numerical levels provide important insights into pregnancy progression. The first blood test for hCG (beta-hCG) is typically performed around 9 to 14 days after embryo transfer. An hCG level below 5 mIU/mL is considered negative for pregnancy, while a positive result is generally indicated by levels greater than 20 mIU/mL, often over 25 mIU/mL.
A healthy initial hCG level around 10-14 days post-transfer can range from 50 to 100 mIU/mL, though significant individual variation exists. The doubling time of hCG is particularly important for assessing pregnancy progression; in early pregnancy, hCG levels typically double every 48 to 72 hours. This doubling rate is a strong indicator of a viable pregnancy, and fertility specialists often monitor this trend with serial blood tests every two to three days rather than relying on a single measurement.
Factors Influencing HCG Rise
Several factors can influence the rate and level of hCG rise after an embryo transfer. Individual biological variation plays a role, as each person’s body responds uniquely to implantation and pregnancy. The type of embryo transfer also contributes to differences in hCG levels.
Fresh embryo transfers may initially show higher hCG levels due to residual hormones from trigger shots used in the stimulation phase, which are not present in frozen embryo transfers. The developmental stage of the embryo at transfer (day 3 or day 5) can also affect initial hCG concentrations, with day 3 transfers sometimes resulting in higher hCG levels. While the number of embryos transferred can lead to higher hCG levels in cases of multiple pregnancies, hCG levels do not definitively predict multiples. The precise timing of implantation, whether earlier or later within the typical window, can also impact when hCG first becomes detectable and its initial concentration.
HCG Testing and Next Steps
After embryo transfer, hCG is primarily tested using quantitative beta-hCG blood tests, which measure the exact amount of the hormone. These blood tests are more sensitive than urine-based home pregnancy tests and can detect lower levels of hCG earlier. Urine tests require a higher concentration of hCG and are generally recommended after a missed period for accuracy.
Following consistently rising hCG levels, the next step typically involves an ultrasound around 6 to 7 weeks of gestation. This ultrasound confirms the presence of a gestational sac and fetal heartbeat. In cases of a negative hCG result, the fertility clinic provides further guidance to discuss future options.