Getting Ready to Get Pregnant: How Your Body Works
After approximately twelve to fourteen days your egg is ripe and mature enough to be fertilized. A sharp rise in estrogen triggers your pituitary to release still another hormone, LH (luteinizing hormone), which signals your egg to pop from its shell and leave your ovary (ovulation). As it does, the fimbria, the fingerlike ends of your fallopian tube, reach down and catch it, and guide it inside.
The deserted shell your egg leaves behind (called the corpus luteum) begins producing the hormone progesterone, which helps to prepare your uterus further for implantation of a fertilized egg.
In the meantime, sperm, which have been deposited in your vagina, swim through your cervix, into your uterus, and down into both fallopian tubes, in anticipation of meeting your egg. Your cervical mucus aids in the transport. In order for a pregnancy to occur, however, sperm must make contact with your egg within twelve to twenty-four hours after ovulation. After this time your egg begins to disintegrate and pregnancy generally does not occur.
Sperm must get inside your egg during this same time frame. To help accomplish this, the head of each sperm (the acrosome) is filled with enzymes that are immediately released on contact with your egg. They help break down the outer coating and allow passage inside.
Once inside, the sperm membrane fuses with the membrane surrounding your egg, and an embryo is formed. Over the next three days, it divides several times. When it reaches the eight-cell stage, it is strong enough to begin traveling down the remainder of your fallopian tube and into your uterus — a journey that takes roughly five to seven days. When it arrives it will — hopefully — implant in your endometrium and begin to grow into a developing fetus.
Each month, at the start of every menstrual cycle, your body begins to prepare you for a new opportunity to get pregnant. This is a five-step process.
STEP 1: EGG PRODUCTION
Starting on the first day of your menstrual cycle (the day you start to bleed), your GnRH messengers sense that FSH is low. In turn your hypothalamus gland sends a signal to your pituitary to begin producing and releasing more of this hormone into your bloodstream. The purpose is to stimulate a new group of follicles inside your ovary to begin producing eggs.
STEP 2: GETTING YOUR UTERUS READY
As your eggs start to grow, the follicles release estrogen. In a natural anticipation of fertilization, these rising estrogen levels stimulate the tissue that lines the inside of your uterus (called the endometrium) to begin growing thicker. This helps to form a spongy nest into which your embryo (the fertilized egg) can easily implant and start to grow.
STEP 3: SELECTING THE EGG OF THE MONTH
Within a few days after the stimulation of your egg follicles, one of them begins to surpass the others in growth and maturity. Called the graafian follicle, it produces what is thought to be the strongest egg, the one you will eventually ovulate.
STEP 4: OVULATION
As your egg of the month continues to mature, it begins to push against the top of your ovary, forming a tiny bubble on the surface. When it reaches its peak maturity, estrogen levels soar. Sensing this intense rise, your hypothalamus sends a second message to your pituitary gland to release the hormone LH, which also shoots into your bloodstream with a rapid surge. It is this fast and immediate rise in LH that stimulates your egg to leave your ovary and travel to your fallopian tube. After this occurs, your endometrium continues to grow thicker in anticipation of the arrival of a fertilized egg.
In addition to the push your egg receives from the hormonal surge of LH, your fimbria, the petal like fingers of your fallopian tube, also play an important role.
Using a gentle sucking action that gently coaxes your egg from its shell, your fimbria actually reach down and massage your ovary just prior to ovulation.
As your egg bursts through your ovary, the fimbria act like a fertility safety net, catching and gently guiding it inside your fallopian tube so that it can meet your partner's sperm and become fertilised.
STEP 5: GETTING PREGNANT
Once your egg is in your fallopian tube, it is ready to be fertilized, but it only remains fertile for about twelve to twenty-four hours, after which time it begins to disintegrate. In order for conception to occur, your partner's sperm must make contact with your egg within the twelve to twenty-four hours following ovulation. You'll learn later how you can ensure that this occurs.
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