Get Pregnant: Your Menstrual Cycle and Fertility

Also see:
Ovulation and Fertility Definitions

Your Cycle and Ovulation Prediction

The menstrual cycle is divided into two parts: pre-ovulation and post-ovulation. The ovarian cycle refers to the cyclical development and expelling of the egg from the ovary. Though the length and regularity of a menstrual cycle may differ, the average duration of a complete menstrual cycle is 28 days (though healthy cycles can run from 21-36 days). Below you will find an overview of a typical menstrual cycle with an image map based on a 28 day cycle length. "Day 1" of the menstrual cycle is the day bleeding begins. Bleeding - or "menstrual flow" - lasts about three to five days.

By the seventh day of the cycle, eggs in the ovaries begin to ripen due to various hormonal changes. Between the seventh and the eleventh days, the lining of the uterus begins to thicken and it is possible to observe changes in the presence and consistency of cervical fluids. After the eleventh day, luteinizing hormone causes the egg that is most ripe to be released from the ovary and begin its travel down the fallopian tubes to the uterus. For women with a 28-day cycle, ovulation (the release of the egg) should take place on about the 14th Day - or the very middle - of the menstrual cycle.

The period after ovulation is called the luteal phase, and it is marked by a salient increase in body temperature. Following ovulation, the egg travels the fallopian tube toward the uterus. If the egg is fertilized by a sperm (conception), then "implantation" should take place in the uterus (if implantation takes place outside the womb, this is an ectopic pregnancy. Ectopic pregnancy can occur in several places - but the most common is in the fallopian tube). Pregnancy begins if "implantation" occurs. If the egg is not fertilized, it will "expire" in about 24 hours.

Without fertilization, levels of certain hormones will decrease, causing the lining of the uterus to break down and shed - otherwise known as menstruation, or a woman's "period". The first day of bleeding is "Day 1" of the next menstrual cycle.

The first part of the cycle, from menstruation to ovulation, may vary from 14 to 20 days in length. The length of the pre-ovulation phase is often different from one woman to another - but it can also differ from month to month for an individual. It is during first part of the cycle that fertilization can occur. Of course, regular menstrual patterns can be altered by illness, insomnia, stress, physical exertion, and physical and emotional changes.

The luteal phase, or post-ovulation (from ovulation to menstruation), is generally the same length for most women - averaging about 14 days. As a rule, the egg is released 10 to 16 days before menstruation, or the start of the next menstrual cycle.

Fertility Dynamics

A woman's fertile period during her menstrual cycle, on average, lasts about 7 days. The most fertile period consists of the few days before ovulation. There are a number of reasons why this is the most fertile time. First of all, the amount of cervical fluid (cervical mucus, CM) increases and the consistency of the mucus changes substantially (from being sticky and cloudy to becoming transparent, white, and slippery). The purpose of this change is to create a healthy medium for the sperm to survive and travel in. Given a fertile environment, sperm can live several days. The egg, on the other hand, can live only 24 hours - so timing is important. At the moment of ovulation, the body temperature begins to rise to create a warmer, more hospitable environment for a fertilized egg. Also, the cervix will start to rise, soften, and begin to open up.

Hormones and Ovulation: The Release of the Egg
Also see:
Ovulation and Fertility Definitions

During ovulation, a number of different hormonal changes take place. Early in the menstrual cycle, a hormone called Follicle Stimulating Hormone - or FSH - enables your ovaries to nurture eggs. Within the ovaries, follicles house each individual developing egg. The follicles that hold the eggs will secrete estrogen. As the menstrual cycle progresses, the follicle containing the developing egg moves toward the surface of the ovary. Immediately before ovulation, the follicle begins secreting estrogen and progesterone. Estrogen helps the uterine lining thicken and expand and increases blood flow to the uterus. Progesterone causes the glands of the uterine lining to form secretions that help nourish a fertilized egg.By definition, ovulation is the process of an ovary releasing an egg from the follicle - permitting the egg to float down the fallopian tubes. On average, the first phase of the menstrual cycle last two weeks. Directly prior to ovulation, another hormonal change takes place - the LH Surge. LH (or Luteinizing Hormone) is the hormone that actually facilitates ovulation: it causes the egg to separate from the ovarian surface. Ovulation predictor tests function by detecting this LH Surge, thus alerting the woman that ovulation is about to take place.

Once released from the ovaries (post-ovulation), the egg can survive for about 24 hours. This means that sperm (which can live several days) must be present to fertilize the egg. Following ovulation, the egg enters the fallopian tubes and continues toward the womb. Typically, conception - the uniting of the egg and the sperm - will take place in the fallopian tube, and then the fertilized egg will continue its passage to the uterus and implant in the uterine wall. For pregnancy to take place, fertilization of the egg must be followed by a successful implantation.

Following ovulation, the luteal phase begins, marked by an increase of the hormone progesterone, which strengthens the uterine lining (endometrium) and causes the body temperature to increase, facilitates changes in the cervical fluid, and alters the position of the cervix .Within 24 hours, if the egg has not been fertilized, it will simply disintegrate after reaching the uterus. Without fertilization - and implantation - the levels of others hormones will ultimately drop during the luteal phase, causing the lining of the uterus to break down and shed - referred to as menstruation, or a woman's "period".

Implantation, Pregnancy & Human Chorionic Gonadotropin

Fertilization occurs when a sperm penetrates the egg - and this typically takes place in one of the fallopian tubes. The fertilized egg (or embryo) then travels to uterus and implants in the uterine lining. At this point, the embryo and developing placenta will begin to release hCG (Human Chorionic Gonadotropin). The presence of hCG will help facilitate the continued production of progesterone - essential for a fertile, hospitable environment for the implanted embryo. The hormone hCG will increase and show up in a woman's blood and urine, making hCG a prime marker for pregnancy detection. Home pregnancy tests function by detecting hCG in a woman's urine.