Do Hormonal Phases Matter?
Pregnancy is a 9-month period where a woman ideally carries a baby to term. However, the lead-up to that shift into gestation is highly complex and relies on a delicate hormonal balance to trigger every step of the process. Depending on which hormones are present and in what quantities, a variety of bodily functions that are all part of the menstrual cycle might begin. Essential steps like thickening of the endometrial lining, triggering egg production, and even ovulation depend on hormonal phases. Just as with natural conception, in vitro fertilization (IVF) also relies on hormonal phases. However, hormone supplementation is a hallmark feature in IVF that can help ensure better success rates.
Hormones and phases
Pregnancy is influenced by 5 specific hormones which include progesterone, estrogen, luteinizing hormone (LH), human chorionic gonadotropin (hCG), and follicle-stimulating hormone (FSH). Of the 5, LH, FSH, and estrogen trigger ovulation. Both estrogen and progesterone influence endometrial thickening. LH is also responsible for triggering estrogen and progesterone. Along with simply being present, specific hormonal phases during a woman’s menstrual cycle also dictate pregnancy outcomes. The 4 phases include the menstrual, follicular, ovulatory, and luteal phases and follow an average 21-35 day cycle.
Menstrual phase
The menstrual phase is usually days 1-5. Also called the period, this time marks the beginning of a woman’s cycle. If implantation doesn’t occur, the endometrial lining sheds from the uterus, causing progesterone and estrogen levels to drop. IVF cycles tend to take 6-8 weeks to complete but isn’t inclusive of any pre-cycle preparations such as testing or even birth control to moderate the cycle. Once the actual IVF cycle begins, the menstrual phase will mark the true beginning and will include ovarian stimulation from day 1-10 or 14.
Follicular phase
While technically the second phase, the follicular phase overlaps with the menstrual phase and covers days 1-13. During this window, FSH begins stimulating ovarian follicles to mature which also triggers more estrogen production. The estrogen works to thicken the uterine lining. For IVF participants, ovulation stimulation is still happening but a trigger shot which is normally hCG, is given anywhere between day 12-15.
Ovulation phase
The ovulation phase usually takes place on day 14 and occurs because of an LH surge. A mature egg is released from the ovaries. For IVF, the trigger shot is given during this window with egg retrieval scheduled within 36 hours of medication administration.
Luteal phase
The luteal phase is the last of 4 stages and is between days 15-28. Keep in mind that every woman’s menstrual cycle can vary in length so the phases may be shorter or longer than the averages listed above. During the luteal phase, a temporary gland develops on the ovaries that releases an egg, called the corpus luteum. The temporary gland secretes progesterone, which thickens and nourishes the uterine lining in preparation for implantation. The IVF egg fertilization and embryo transfer steps are timed with this window and usually occurs between days 16-21.
The IVF difference
In natural conception, controlling for hormone levels or even moderating menstrual cycles is less common. With IVF, depending on any underlying conditions that might be present as well as more traditional operating practices, a woman will receive various hormone supplements. The medications work to boost egg production and endometrial thickness, and to regulate menstrual cycles to time the process accurately. Women thinking of trying IVF should speak with a specialist to better understand the process.
