How Pregnancy Occurs
In order to prevent an unwanted pregnancy, it's important to know exactly when
you can get pregnant and how it can happen. Pregnancy involves three basic steps:
ovulation, fertilization, and implantation.
Ovulation
During ovulation, a woman's ovaries release a mature egg or eggs. The egg
travels down the fallopian tube towards the uterus where it will remain,
awaiting fertilization. A woman is most fertile 7 days before ovulation and
up to 2 days afterwards. Nevertheless, it is possible for a woman to get
pregnant any day of her menstrual cycle.
Fertilization
The egg will remain in position for 72 hours but can only be fertilized
within the first 12 - 24 hours. During vaginal intercourse a man will
ejaculate 1.5 - 5 milliliters of semen containing approximately 20 - 150
million sperm per ml. This may sound like a lot, but the journey to the
egg is an arduous one and only about 1% of sperm actually make it.
Of those that do, only one enters the egg.
Implantation
Once fertilized, the egg travels the remaining length of the fallopian
tube and arrives in the uterus three to four days later. Implantation
occurs if the embryo attaches to the uterine lining. This is a critical
step in the pregnancy. As many as 50% of fertilized eggs are flushed out
of the body (during menstruation) before implantation can occur.
Ways You Can Get Pregnant
Vaginal intercourse is by far the most common way to get pregnant. A woman
may also become pregnant whenever semen comes in contact with the vagina.
For this reason, withdrawal and outercourse may not be effective means of birth control.
Alternative insemination and in vitro fertilization are also possibilities.
During alternative insemination sperm are placed into the woman's uterus
using a syringe. In vitro fertilization is a process by which eggs are
removed from the woman's body, joined with sperm, and placed back in her body.
Preventing Pregnancy
Each of the five types of contraception can prevent pregnancy in a different way.
Behavioral methods are natural sexual practices that prevent the union of egg and
sperm. Barrier methods involve a physical or substance barrier that prevents
sperm from entering the uterus. Hormonal methods manipulate the hormones associated
with reproduction (estrogen and progestin). This prevents the release of eggs.
Emergency contraception prevents the release of eggs and makes implantation more
difficult. Male sterilization blocks the vas deferens so the sperm can not enter
the seminal fluid. Female sterilization blocks the female fallopian tubes so the
sperm can not reach the egg.
Recognizing the Signs of Pregnancy
Every woman is likely to have a few pregnancy "scares" in her lifetime.
Knowing the signs of pregnancy can help you determine if a scare is real.
The first and most obvious sign of pregnancy is a missed period. By this time,
a pregnancy test can fairly accurately determine whether or not you are pregnant.
Other early pregnancy symptoms may include: nausea, fatigue, bloated feeling,
the urge to urinate more frequently, mood swings, and tender breasts. You may
not experience all of these symptoms but if you experience one or more of them,
it could indicate you are pregnant.
Resources
Beus, T. (2001). Knowing Your Menstrual Cycle. Retrieved February 7, 2010, from the Women's Health Web site:
http://www.womenshealthlondon.org.uk/leaflets/cycle/cycle.html
Dugdale, D.C. (2008). Semen Analysis. Retrieved February 7, 2010, from the Mediline Plus Web site:
http://www.nlm.nih.gov/medlineplus/ency/article/003627.htm
Mazumdar, M.D. (n.d.) How Pregnancy Occurs. Retrieved February 6, 2010, from the Gynae Online Web site:
http://www.gynaeonline.com/normpreg.htm
Planned Parenthood® Federation of America Inc. (n.d.) How Pregnancy Happens. Retrieved February 6, 2010, from the Planned Parenthood Web site:
http://www.plannedparenthood.org/health-topics/pregnancy/how-pregnancy-happens-4252.htm
