When Did I Get Pregnant or Conceive?

Many women, upon finding out that they are pregnant, try to figure out the exact day the pregnancy began. This happens for several reasons: curiosity, due date estimation, or paternity issues.

No matter what the reason, finding out the exact day that pregnancy began can be tricky. Here's how to find out around what day you conceived by:

• Understanding your menstrual cycle
• Calculating the date of ovulation
• Figuring out the date of conception

The best way to calculate the day you likely conceived is to figure out approximately when you ovulated. Ovulation occurs about 10-14 days before your period each month. So if you had sex during this fertile window, then it is possible that you conceived during those days.

Ovulation is the time when you can conceive, so it is important to figure out what days you ovulate. Ovulation usually occurs in the middle of a woman's monthly cycle. For most, it occurs 10-14 days before your next period. You will need to subtract 10-14 by the length of your cycle.

Let's say you have a period starting on January 1st, and you have a 30-day cycle. To find out when you will ovulate, you need to count back 10-14 days from January 30, which would be around January 16th-20th. Therefore, your most fertile days, and the days you most likely conceived, would be around the 16th of January to about the 20th.

Here's another example:

Let's say you have a period on June 28th. Since June 28th is the first day of your cycle, ten to 14 days before your next period would be around July 14th to July 18th, which is when you'd be most fertile and more likely to conceive.

Note: These examples are based on a 30-day cycle. If you have a longer or shorter cycle, you should calculate your ovulation by subtracting 10-14 from the number of days in your cycle or by using this ovulation chart. On average, many women ovulate around these days. Those with irregular periods or who do not ovulate all of the time may not be able to rely on this method.

If a woman has intercourse during her ovulation period, she may be able to conceive. The exact moment of conception is debatable, but it begins when a sperm burrows into the egg within 24 hours after ovulation. Some say conception is right at the moment when sperm meets egg; others say it is when the combination of sperm and egg implant into the uterus.

When does it actually happen? Let's say you ovulate on day 10 of your cycle. The egg comes out of the ovaries and waits for 24 hours in your fallopian tube. There's two possibilities of what could occur:

1. Sperm from intercourse 3-5 days ago can meet the egg in the fallopian tube and fertilize the egg.
2. Sperm from intercourse that day or the day after can meet the egg in the fallopian tube and fertilize the egg.

If you have intercourse during day 7 of your cycle and you ovulate on day 10, it's possible that conception can begin on day 10 or 11, depending on how quickly the sperm finds the egg. If you have intercourse on day 10 or your cycle, the same day you ovulate, conception can begin that day or the 11th day.

Sperm can live for up to five days inside of a woman's body after intercourse. In some rare cases, and with perfect conditions, some sperm may even live up to seven days after intercourse!

Strong, healthy sperm can reach a woman's fallopian tubes in as little as 30 minutes, while it may take others several days. If an egg is there within the 30 minutes, conception can occur right then. If the egg is not there yet, the sperm can live a few days in the fallopian tubes and fertilize the egg once it is released.

Sperm can live inside a woman's body for up to 7 days. An egg is viable for 12 to 24 hours after ovulation. This means you can get pregnant from having sex 7 days before ovulation and 1 day after.

• Changes in cervical fluid: Your cervical mucus will be clear and stretchy, like egg white.
• Change in basal body temperature: After you ovulate, you will see a rise in temperature. You need to track your BBT over several months in order to predict when ovulation occurs.
• Change in texture and position of cervix: During ovulation, the cervix is open and becomes softer and is positioned higher up.
• Mild cramping: Some women report feeling a twinge on one side of their lower abdomen. This is known as mittleschmertz, and it should only last a few hours, if at all.
• Light spotting: This is rare, but some women may experience light spotting when they wipe. Bleeding should not be heavy, red, or last more than a few hours.
• Mild bloating: A rise in oestrogen levels prior to ovulation will trigger the release of LH (luteinizing hormone). This surge in hormones causes water retention, which leads to feelings of bloat.

An average menstrual cycle usually lasts anywhere from 26-35 days in length. During this time, a few things occur:

• Days 1-7: You will have a period. This is when the uterine lining is shed if there is no pregnancy.
• Days 10-14: This is your fertile period, or ovulation, when an egg is released from the ovaries. This will likely be the time when you conceive.
• Days 15-35: If you get pregnant, this is when implantation occurs. This stage is also known as the luteal phase.

This is an average cycle for many women. For those with irregular cycles, calculating your ovulation period can be tricky, and there is no real way of predicting when ovulation occurs without some type of hormone testing, which can be done with an over-the-counter ovulation predictor kit or blood test.

Unless you have taken some sort of hormone test to determine the possibility of ovulation, there's no real way of knowing when you would exactly ovulate. Some women do experience symptoms of ovulation, but most do not and can only make a guess as to when it could occur.

This is why women with regular cycles use the estimation of ovulation happening within the 10th-14th days of their cycle. The exact moment of ovulation is still not quite possible to pinpoint, but based on cycle regularity and monitoring of some of the common symptoms, it can be estimated when you may be ovulating.

Once sperm and egg have met and the egg is fertilized, the egg becomes a tiny ball of cells and travels down into the uterus. If it is a viable pregnancy, meaning that the ball of cells is growing normally, it will try to implant or burrow into the lining of the uterus where it can grow into a baby.

This process of implantation can happen about 7-10 days after ovulation, more or less. If you ovulate on day 10 of your cycle, implantation could occur anywhere from days 17-20 of your cycle. Basically, it happens about a week before your next expected period.

Most women do not realize that implantation has occurred, but some women do experience some symptoms:

• Implantation bleeding or spotting that is brownish, pinkish, or reddish and is lighter than that of period bleeding. It should also only last a few days. If implantation bleeding lasts for longer than three days, then you may have a health-related issue, such as an ectopic pregnancy.
• Slight cramping that is intermittent and lasts for less than three days. Some women may confuse implantation cramping for PMS cramping.

Once implantation has occurred, the embryo continues to grow and develop. This triggers a hormonal response from the body, which tells the body not to shed the uterine lining in the period. The hormone responsible for this is human chorionic gonadotropin, or hCG. It is the same hormone that is used by home pregnancy tests to indicate a pregnancy.

On average, a baby arrives 240 days (40 weeks) after the first day of your last menstrual period. This is the gestational age, and it is what most doctors and health care professionals use to calculate the due date. It includes the two weeks prior to conception when a woman is not pregnant. Of course, this is based on a 28-day cycle, and days will need to be adjusted for longer or shorter cycles. But, even with adjustments, less than 10 percent of women actually deliver on their calculated due dates, so giving birth two weeks before or after the estimated due date is normal.

How Do You Calculate Gestational Age?

Gestational age is measured in weeks. To figure out the gestational age, you take the first day of your last menstrual cycle and count how many weeks it has been up to the current date. Delivery will usually occur around the 38th or 40th week.

Why Do They Use the Last Period to Date a Pregnancy?

It is nearly impossible to know the exact date of conception, so doctors start with the first day of the last known menstrual cycle. A baby's actual age is called the "fetal age," and this age is two weeks less than the gestational age because it doesn't include the two weeks prior to conception. Doctors like to use gestational age because it is easier to count from a woman's last period than to guess when a baby was conceived. A baby can be delivered and survive any time from the 22nd week of pregnancy to the 41st week. Of course, the further along the pregnancy is, the better chance the baby will have of surviving without medical intervention.

Example: If your last period was June 28th, your estimated due date is April 4th. Does that mean you conceived on the 28th? No. Conception most likely occurred two weeks after, during the days of July 8th-July 12th.

Very few women actually deliver on their due dates. The due date is an estimation of when the baby could come. The baby and your body actually decides when the time is right for the baby to be completed with development and to be delivered.

Question: If your due date is April 4th but you deliver on March 28th, does that change the conception date?

Answer: No. Your conception date basically remains the same. It just means that your baby was ready to enter the world a few days sooner than expected!

Within the first two months of pregnancy, a woman will have her first ultrasound scan. Most of the time this is done to determine the due date, but sometimes it is done just to make sure the pregnancy is progressing normally.

From the scan, doctors can determine an estimated due date and a possible conception date. These dates are based on the measurements of the baby and of the uterus and how they correspond to average measurements.

Sometimes, the dates given from this scan can be off by a few days. For instance, a woman may think she is about 12 weeks and 3 days pregnant with a due date of August 10th and a conception date of November 17th, but her scan says she is about 13 weeks pregnant with a due date of August 6th with a conception date of November 13th. Does it change anything? Not at all. It just means that the measurements from the scan correspond to someone who is 13 weeks pregnant, and the dates are estimated based on that.

Scans given early in pregnancy are known to be off a few days, but later on in the pregnancy, the scans tend to be right on target. The only time a scan would indicate you were further along in pregnancy during late pregnancy is when the baby is larger than expected, either due to genes or macrosomia (a condition where the baby grows to be large, sometimes due to gestational diabetes).

Just like basing your due date from your last period is an estimate, an ultrasound scan gives fairly accurate estimates about when your baby is due and when he or she was conceived.

If you have been with more than one man during your cycle, you may be wondering: "Who is the father of my baby?"

You can use your dates to try to figure it out, of course, but your best chance at knowing without a doubt who the father is would be to have a paternity test done once the baby is born.

If you would like to try to figure it out and you have regular cycles, here's how:

1. Using a calendar, mark your last period on the calendar and figure out your possible dates of ovulation (use the information above). Mark your possible days of ovulation with an 'O'.
2. Think of each time you were with someone. Using #1 and #2 (and so on), mark each encounter on your calendar.
3. Do any of the #s fall within your ovulation dates?

Once you have your calendar marked, it's time to analyze. Start with the first man. Were you with him any time leading up to ovulation or during ovulation? If so, he could be the father. Same thing with the second man, and so on.

Look at the Following Scenarios and See If Any Apply to You

Scenario 1: You were with Guy #1 on June 20th. You got your period around June 28th. You then were with Guy #2 from July 1st-3rd, and July 11th-13th.

Who is the father? Guy #2 would be the father since you had a period after Guy #1. Also, you were with Guy #2 during your fertile time.

Scenario 2: You have your period June 28th. You were with Guy #1 on June 29th, July 3rd, and July 5th. You were with Guy #2 on July 7th-11th.

Who is the father? Guy #2 is most likely the father since you were with him closest to your fertile time. If for some reason, however, you ovulated sooner than the 10th of July, there's potential that Guy #2 could be the father since his sperm may have lived from the 5th-10th. In this case, I suggest a paternity test so there aren't any doubts.

Scenario 3: You have your period on June 28th. You were with Guy # 1 on the 10th of July, and you were with Guy #2 on the 12th of July.

Who is the father? There's no way to know without a paternity test. Since you were with both men so close together, it's possible that both of their sperm were in you when you ovulated and either one could be the father.

Again, a paternity test would be the sure way of knowing who the father of your baby could be. Once the baby is born, the test can be done and no one will have second guesses.

While it is possible to determine paternity during pregnancy, the tests aren't recommended for basic cases. Why? Prenatal paternity tests can be invasive tests, meaning that a needle needs to be placed into the mother's abdomen and into the space where the baby is growing.

Paternity can be determined using amniocentesis where amniotic fluid is drawn through a needle, or chorionic villi sampling where tiny pieces of the chorionic villi found on the lining of the uterus are removed using a thin tube or a needle. Both carry slight possibilities of miscarriage, which is why they are not recommended for paternity testing alone.

There is a method to try to find the DNA of the baby in the mother's bloodstream during pregnancy, but this method is not 100% reliable.

For more information, visit the American Pregnancy Association website.

Your date of conception, or the date of when you became pregnant, is an estimated date that can be figured out using the date of your last period. By knowing more about ovulation, conception, and implantation, it's easy to see how the date of conception is an estimated date since it's nearly impossible to pinpoint any of the three times in your cycle.

Even though it's an estimated date, knowing when you may have conceived can help with figuring out due dates and other pregnancy-related issues.

Best wishes with your pregnancy!