Probable Date of Conception

Many women want to know their probable date of conception when they find out that they are pregnant. Although it can be easy to guess which week the big day occurred in, narrowing it down to a specific day is tricky.

Although the month is easy to figure out, the actual day of conception may be hard to determine.

Most women with regular cycles ovulate around 14 days before their expected period. In a regular 28-day cycle, this is also 14 days after her last period. So, a woman who had her period on October 1 would likely ovulate on October 14.

After ovulation, the egg can be fertilized for up to 24 hours. Even though ovulation might occur on the 14th, she could also conceive from intercourse as late as the 16th. Likewise, sperm remains viable for about 72 hours, so a woman who ovulates on the 14th can conceive from sex on the 12th since the sperm will still be viable when ovulation occurs. Most women have a 4-5 day window of their most fertile time each month.

Although science has discovered that most women have a 28-day cycle with ovulation on day 14, women's bodies don't care what the research says. A woman might have what appears to be a regular cycle, but she could ovulate on day 13 or 15. If a woman has never tracked her ovulation by using tracking her basal body temperature or ovulation predictors, she might not realize that her cycle is just a little bit different.

There are also many things that can happen during the month to affect a woman's ovulation date. Illness, stress, exercise, and medications that contain hormones all play a factor in ovulation, which can also influence a woman's probable date of conception if she conceives during this time.

Because of the uncertainty of when conception actually occurs, it's next to impossible to conclusively know when a woman conceived. A woman using ovulation predictors who is tracking her cycle might know that she is going to ovulate on the 14th and plan intercourse for the same day. There is a pretty good chance that the 14th then is the day she conceived. But if the egg and sperm don't meet up right away, or if she ovulated a few hours later, she could conceive on the 15th.

In the bigger picture of having a baby, it seems like no big deal if a woman's probable date of conception is a little bit off. Physicians used to rely on the date of a woman's cycle to calculate a likely conception date by just adding 14 days to the start of the last period. Now, ultrasound images and blood tests give a more accurate look at when a baby was probably conceived.

This extra information, however, is confusing to some moms who thought they knew when they conceived based on their ovulation date. It's not unusual for a woman to find out that she is actually several days further into a pregnancy than she expected or that she isn't as far along as she thought.

As long as the date the doctor estimates for conception is within a week or so of ovulation, there really isn't anything to be concerned about. It's only when the conception date is much earlier than expected that a woman needs to be concerned about whether or not she has been getting the proper prenatal care and nutrition.

The reason most women are concerned about determining a probable date of conception is because it helps estimate a due date. But, neither the woman's body nor the baby pays any attention to the calendar. Most babies will be born healthy within a few days of the estimated due date. Very few women actually deliver on their exact due date, so the difference of a few days between when a woman may have actually conceived and when she is estimated to conceive don't make much of a difference.

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