Your Fertility Cycle
The Menstrual Cycle
Hormone levels rise and fall throughout the menstrual cycle, coordinating the events that take place. For a woman to have the possibility to become pregnant, hormones released from the ovaries and the brain must work together during her cycle. This allows for egg maturation and fertilization, and prepares the uterus for embryo implantation.
The Follicular Phase
The menstrual cycle begins with the follicular phase. The main purpose of the follicular phase is to grow mature follicles in the ovaries and promote ovulation. Under normal circumstances, an egg resides in the follicle.
Two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH), are released from the brain and help stimulate growth of follicles. The follicles will continue to mature until there is a surge in the level of LH, which triggers ovulation. While many follicles form during a normal cycle, only one of the largest is selected for ovulation; this is called the dominant follicle. During ovulation, the mature egg in the dominant follicle is released from the ovaries and is ready for fertilization.
A woman is most fertile during ovulation. Another hormone, estrogen (estradiol, or E2), is released from the ovaries during the follicular cycle, and helps to regulate ovulation and uterine lining growth.
The Luteal Phase
The second phase of the menstrual cycle is the luteal phase, which begins with the onset of ovulation. This phase involves the preparation of the uterine lining, called the endometrium, for potential embryo implantation. A large spike in progesterone levels, another hormone produced by the ovaries, stimulates uterine lining growth to create a friendly environment for a developing embryo.
If pregnancy does not occur, progesterone as well as estrogen levels drop, and the lining of the uterus is shed through menses. With the onset of menses, the menstrual cycle begins again with the follicular phase.
If pregnancy does occur, the menstrual cycle is put on hold for the duration of pregnancy, and the uterine lining is kept to nourish the growing embryo.
Fertilization and Implantation
After ovulation, if sperm is present, an egg is fertilized in the fallopian tubes. The fallopian tubes serve as the pathway from the ovaries to the uterus. A fertilized egg prior to any development is called a zygote. The zygote develops for five to seven days within the fallopian tubes, undergoing several cellular divisions, before becoming a blastocyst. At this stage, the embryo will implant into the uterus. Eventually, this embryo develops into the fetus.
To Request an Appointment
Northwestern Medicine Fertility Center is now conveniently located in four locations: Chicago, Geneva, Highland Park, and Oakbrook Terrace.
Visit our Locations & Appointments page for more information.