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When can a woman get pregnant?

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When are women fertile? Knowing when a woman can get pregnant is essential in a heterosexual relationship. If you are wanting to conceive a baby, it helps to know when the best time for intercourse is. If you do not want a pregnancy, you must use contraception to avoid it, or abstain from specific types of sex during a specific time of the month.


You will find it much easier to understand the following passage after reading up on female sex hormones and the reproductive cycle. The female reproductive cycle lasts on average between 24 to 35 days. It consists of 4 distinct phases: the menstrual phase, the pre-ovulatory phase, ovulation itself, and the post-ovulatory phase. The only fertile period during a woman's cycle is just before, during, and just after ovulation.


During the pre-ovulation phase follicles grow within the ovaries of a woman. They release the sex hormone estrogen. This hormone builds a positive feedback loop with another hormone, called luteinizing hormone or LH, which is released from the pituitary gland in the brain. Each hormone stimulates more of the other hormone to be released during the pre-ovulation phase until the concentration of LH reaches a threshold. At this point the high amount of LH will trigger ovulation.


Ovulation is the process whereby the most dominant follicle out of a group ruptures and releases one single egg. This egg, or the medical term is oocyte, is caught by the Fallopian tubes, which envelope the ovaries. The egg then continues to travel down the tube to the uterus, a journey which will normally take about 7 days.


Fertilization of the egg is the process whereby the egg and a sperm cell fuse. This triggers further development of the egg cell, which results in a tiny bubble of cells called a blastocyst, which implants itself in the inner lining of the uterus. Here the tiny cluster of cells can grow into an embryo, which is protected and nourished by the uterine lining.


At the moment of fertilization a pregnancy is possible. However, many fertilized egg cells do not implant themselves properly or are lost somewhere during the process.


The only way to avoid a pregnancy for sure is to not introduce sperm into the vagina during a specific time of the month. The released egg cell survives inside the Fallopian tube without fertilization for 24 hours after ovulation. If fertilization has not occurred by then the egg cell dies and no pregnancy is possible during that month. Sperm cells can survive for about 48 hours inside the vagina. This results in a window of 3 days during which most pregnancies occur: 2 days prior to ovulation and 1 day after ovulation. To give this time period some extra leeway to account for natural variation, a woman is fertile during 4 to 5 days surrounding ovulation.


Unfortunately, it is not as easy as it sounds. The natural cycle in a woman can show strong variations. Normally, ovulation occurs about 14 days after the end of the last period. However, the pre-ovulatory phase is the most variable on in the cycle. Stress, nutrition or living around other women can influence a woman's cycle. Most women are not able to feel when they are ovulating and there are no obvious outside signs that this process is happening. Therefore, the actual time period during which the use of contraception to avoid pregnancy is necessary is much longer then 4-5 days, depending on how safe you want to be.


Finally, a word on introducing sperm into the vagina. The most obvious way to do so is through ejaculation during intromission, when the penis is inside the vagina. However, sperm, which is deposited on the outside the vagina on the vulva can make it's way inside and result in a pregnancy. If you are masturbating together care must be taken to avoid contact of sperm with the outside of the vagina, not just the inside. The same holds true for anal intercourse. If the man ejaculates it is possible that sperm trickles down the perineum of the woman to the outside of the vagina.


Additionally, sperm is ejected from the penis not only during ejaculation. Many men secret little droplets of fluid when they get aroused from the tip of the penis. These drops not only aid lubrication, but will also already contain some sperm.


If you are using a condom for birth control you must apply the condom before the penis first enters the vagina. It is possible to get pregnant if you only apply the condom after some thrusting has already occurred.



Source for the facts cited in this page: 

Francoeur, R. (1995) The Complete Dictionary of Sexology. New expanded edition. Continuum New York

Principles of anatomy and physiology (2000) Ninth edition by Gerard J. Tortora and Sandra Reynolds Grabowski. Publishers: John Wiley and Sons


Written by Anna, 16.08.07

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