If I have sex with my wife tonight, when is the latest that she can become pregnant? Let’s say she doesn’t ovulate for a week, or two. Can she still get pregnant as a result of tonight’s activities?
No. As a matter of fact much of the sperm is killed only a select few make it the egg. I do not remember the parts per million, but there is a large number of sperm that simply do not make it. That is why it can take some time for some couples to get pregnant.
Check this link for a great article.
This is another great article, that deals primarily with the fertility window. It may be more useful than the first link. This one gives the fertility window of 5 days, but there are factors that affect it. Check the bottom of the page in fertility window section.
When she ovulates isn’t an exact science, and can vary wildly. Trust me on this one. Around my house, they call me “Daddy”.
I don’t think the question was about when the woman ovulates, I think it was asking how long sperm can live in the female body.
My first answer was “three days”, but I got that from sex ed (er, excuse me, “human growth & development class”) in sixth grade. Og only knows how accurate any of that information actually is.
Googling around I found this:
http://forums.obgyn.net/pregnancy-birth/P-B.9905/0292.html
Which seems to confirm three days. I still wouldn’t be suprised to find that number signifcantly off, though.
In humans the limit is about 5 days, but that’s an exceptional case. Two days would be more usual. Most other mammals are similar, but some animals are much more impressive. The record in turkeys is 110 days, and 45 days is not unusual. It has been suggested that in such long-term storage, the sperm are somehow nourished by the female’s body until she’s ready to use them, but the process is not well understood. My source is the book Promiscuity by Tim Birkhead.
If you really care, you can read Taking Charge of Your Fertility by Toni Weschler. It all depends on the woman’s cervical mucus. Women who have good quality mucus can be fertile for 5 days or more, the average is 3 days, some women only 1 day. The sperm live in the mucus. If it isn’t the right pH or consistency, they die. They have to stay alive in teh vagina on the cervix until the cervix opens, which is usually only open for 24 hours around the time of ovulation.
If you really care, you can read Taking Charge of Your Fertility by Toni Weschler. It all depends on the woman’s cervical mucus. Women who have good quality mucus can be fertile for 5 days (possibly more, but if so, there is no scientific proof), the average is 3 days, some women only 1 day. The sperm live in the mucus. If it isn’t the right pH or consistency, they die. They have to stay alive in the vagina on the cervix until the cervix opens, which is usually only open for 24 hours around the time of ovulation.
As a side note, generally the X chromosome sperm are heavier and hardier, so you are more likely to have a girl if you have sex before ovulation and more likely to have a boy if her cervix is open at the time of release, as the smaller Y sperm are faster.
So before you marry her, ask her about the quality of her cervical mucous.
Thanks for the answers. As a followup, how long after the union of the sperm and egg can pregnancy be detected by a blood or urine test?
sorry for the late hit - A blood test by the doctor’s office can detect any time after implantation, which is usually 6-8 days after fertilization. Your run of the mill at home urine test usually can’t tell until 14 days after fertilization. There is one at home brand that says you can test 10 days after fertilization, but they are new and I have not been trying for 4 years or so, so the brand escapes me.
Best of luck to you for whatever your desired outcome is.
Given the (normative) 3 days of motility of sperm and the only 2-3 day window of implantation of the ovum while it’s traveling down the fallopian tube, that means that in a woman’s menstrual/ovulation cycle, there is only a 4-6 day period when pregancy can occur.
Outside that time frame (the other three weeks of the month), you can go at it like [insert sex-crazed metaphor here], without any fear of pregnancy.
So, it all boils down to determing when ovulation is taking place. In the old ‘rhythm method,’ a woman would count the days since menstruation to guess when the next ovulation would take place. Unfortunately, not all women’s cycles are regular, and even a woman with a regular cycle can be thrown off by sickness or stress. That’s why the rhythm method is no longer encouraged.
The new alternative to the rhythm method is called “Natural Family Planning.” This relies on using bodily symptoms like bodily temperature and the above mentioned viscosity of vaginal discharges to determine very precisely when ovulation occurs. The World Health Organization of the UN teaches NFP to woman in third world countries because:
[list=1]
[li]There is none to almost no cost involved.[/li][li]It is proven to be as effective as the pill or condoms (WHO’s statistics, comparing those who actually practice the various methods and discounting the ones who gave up on it.)[/li][li]The woman does not have to rely on the man to participate… it’s a take-charge thing.[/li][/list=1]
And, lest you think that NFP is solely the provenance of Catholics and nature-freaks, talk to your doctor about wanting to become pregnant and the first thing you’ll hear is, “Natural Family Planning.” [Because it determines very accurately when conception can take place.]
Peace.
Not to mention: no hormone pills and no condoms.
OK, there is the abstinence for every one out of four weeks thing…
About nine months, give or take a couple weeks 
Go over to http://www.webmd.com and do a search on pregnancy test and ovulation. It’ll explain it beautifully.