Clearblue Fertility Monitor, Instruction Booklet

Page: 5 / 48

3
Understanding Ovulation and
the Menstrual Cycle
The Menstrual Cycle
• The menstrual cycle is the process during which your
body prepares for pregnancy. Hormone changes
during the cycle trigger the ovaries to release an egg.
• The eggs are contained within fluid-filled cavities called
follicles. Both ovaries have many follicles, each
containing an egg. During the first part of the
menstrual cycle, one of the follicles prepares to release
an egg. This follicle produces increasing amounts of
estrogen, which causes the lining of the uterus to
thicken and the cervix to produce ‘fertile mucus’.
This ‘fertile mucus’ is important (refer to page 4).
A high estrogen level triggers the surge of another
hormone, luteinizing hormone (LH). Ovulation normally
occurs 24 to 36 hours after the LH surge, when the
follicle ruptures, releasing an egg.
• The egg can be fertilized for up to 24 hours after
ovulation. If fertilization does not occur, the estrogen
level will gradually fall. The lining of the womb is shed
and the menstrual flow begins, marking the start of the
next cycle.