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Positive Pregnancy Test: When Did I Conceive?

When exactly does pregnancy begin?

If you’ve got a positive pregnancy test, you likely have a lot of questions. One of them may be wondering exactly when you conceived. Unfortunately, it’s very difficult to determine the exact day you got pregnant.

Even if you only had sex one time during your cycle and became pregnant, it’s possible that the day you had sex was not the day you conceived. That’s because sperm can survive inside the vagina for up to five days after sex, waiting for an egg to become available during ovulation.

And because no woman’s body is a clock, and ovulation occurs on different days each cycle, it’s easy to be unsure of conception date.

So, how do you find out the day you got pregnant? The most common way doctors date a pregnancy is off the date of your last period. So, if you’re wondering “how pregnant will I be” by the time you miss your first period, a doctor would inform you that you are one-month pregnant.

Unfortunately, if you’re waiting for your first missed period, asking yourself “Have I conceived?” it’s tough until you get a positive pregnancy test to know for sure.

Understanding Ovulation

If you’ve gotten a positive pregnancy test and are trying to determine if or when you’ve gotten pregnant, it’s important to understand just how ovulation and conception works.

When does implantation occur after ovulation?

Implantation is the process in which a fertilized egg becomes embedded in the uterus and starts to grow. In most pregnancies, this begins about eight to 10 days following fertilization (the date you have unprotected sex).

Many people wonder, “Can you get pregnant the days before and after ovulation?” You should know that it is possible to get pregnant around the time of ovulation. That’s because even though you are only able to get pregnant if an egg is present, sperm can survive in the vagina for up to five days after sex.

If you are close to ovulation, the sperm can survive long enough to be present for when an egg is released from the fallopian tubes, allowing it to become fertilized even if you didn’t have sex on the exact day of ovulation.

On the other hand, can you get pregnant right before your period? In most cases, no. That’s because after ovulation comes the luteal phase of the menstrual cycle — the time when your body is preparing for a possible pregnancy, but also menstruation if a pregnancy has not occurred.

During the luteal phase, a fertilized egg would implant in the uterus and hormones would work to help the start of a pregnancy. During this time, no more eggs are released from the fallopian tubes, meaning the body has shifted from trying to get pregnant to trying to support a pregnancy. That means it’s not possible to become pregnant.

Still — for women with irregular cycles or abnormally short cycles, it is possible to get pregnant during a period. That’s because the shortened cycle decreases the number of days leading up to ovulation, and combined with sperm’s lifespan, can lead to pregnancy.

How to figure out when you ovulate

For women who track their cycles through an app, or through basal body temperature tracking, you can use prior cycle information to determine when you may have ovulated. While ovulation varies from month to month, and it is nearly impossible to determine the exact date of ovulation, most women with a 28-day cycle can expect ovulation to occur around day 14 (essentially two weeks following the first day of their period).

Still, you should know that every cycle fluctuates, meaning it’s possible to ovulate early (such as on day 12) or late (such as on day 17) depending on the length of your cycle. Women with cycles longer than 28 days may ovulate later, while women when cycles shorter than 28 days may ovulate earlier.

Symptoms during ovulation

Even though it can be hard to determine when exactly you ovulate, it is possible to use your body’s clues to understand if ovulation is about to occur. If you’re trying to calculate how pregnant you are, or wondering what cycle day did you conceive, you can think back to when you may have experienced ovulation symptoms.

Some common symptoms of ovulation include:

  • A drop in basal body temperature, indicating that ovulation is about to occur
  • Changes in cervical fluid, becoming more slippery and “egg white”-like
  • Changes in the cervix, becoming higher up, soft, and wet-feeling
  • Increased sex drive or interest in sex
  • Light cramping on one side of the pelvis (often called mittelschmerz)
  • Breast tenderness

Combining ovulation symptoms you recall with an understanding of your cycle can make it easier to determine what cycle day you conceived.

How to Calculate Your Conception Date

Calculating your exact conception date is nearly impossible, but it is possible to calculate a small window in which you likely conceived. If you’re wondering “when did I conceive and how many weeks am I,” one of the best clues is to use the date of your last known period.

On the flipside, if you’re asking “when did I conceive based on how far along I am,” you should know that you can count backward to your last period to determine a possible conception date.

Generally, most doctors date a pregnancy based on your last menstrual period (LMP). If you have a regular cycle (around 28 days), you can estimate that ovulation took place around day 14 of your cycle.

So, if you’re trying to figure out when you conceived and how far along you are, think back to your last period, and add 14 days from the first day of menstruation. You can use this date to estimate when you may have conceived, and count from there how far along you may be.

If you know how far along you are, you can count back to your last period and add two weeks to determine the date of conception. For example, if a doctor says that you are 8 weeks pregnant based off your last period, you can count 14 days from the first day of your last period and use that date as a likely conception date.

In this example, a woman who is 8 weeks pregnant likely conceived about 6 weeks prior.

Knowing this, many people wonder: are conception dates accurate. It’s difficult to say, because you may have noticed that doctors date pregnancies based on your last period even though you would not have been pregnant that day, and base medical decisions off that date.

That’s because conception dates are difficult to pinpoint. Many women who know the window of conception use that information when making pregnancy and medical decisions going forward, because they can be rather accurate considering ovulation occurs in a small span of time.

However, for women with abnormal cycles or fertility issues such as PCOS or endometriosis, trying to pinpoint a conception date is difficult and may not be accurate.

Is dating from the last menstrual period (LMP) inaccurate?

Most doctors and OBGYNs date pregnancies based on the first date of the last menstrual period. While this is not exactly accurate, most doctors consider it the best shot at dating a pregnancy before an ultrasound.

In most cases, doctors will date a pregnancy based on the last menstrual period and add 280 days to a date to determine a baby’s due date. In many cases, early ultrasounds are now used to verify this date off a fetus’ measurements up to 13 weeks of gestational age.

How accurate are conception calculators?

Conception calculators can be a great tool at determining when you got pregnant for women who have regular cycles and are knowledgeable about when their last cycle began. Conception calendar calculators work by inputting your due date to estimate when you likely became pregnant.

These calculators simply subtract 280 days from your estimated due date to give you an idea of when you became pregnant. Other tools, such as reverse conception calculators can be used to determine the date of conception based on your last menstrual period, counting forward about 14 days to determine when you may have been fertile.

So, can a conception calculator be wrong? Absolutely! Conception planners and a conception date calculator based on birthday (that of your baby) are often based around an average 28-day cycle. Still, these calculators can’t anticipate that the human body isn’t a clock, and that there are major variances between different women, or even the same woman’s cycles.

The best pregnancy calculators available online will not only give you options for estimating conception date based on your due date, but also your last missed period. They’ll also give options for modifying the number of days in your regular cycles.

If you’re looking for a pregnancy week calculator by due date, which explains what happens week by week during your pregnancy, many will walk you through all 40 weeks, from estimated conception to birth, detailing the changes you and your baby will undergo.

Many pregnancy calculators, such as YourDueDate.com, will also let you input dates in the future, which can help if you are trying to determine the best time to get pregnant in the future.

How to Calculate Gestational Age

There are several different ways to determine how far along your pregnancy may be. Gestational age uses the fetus’ age to determine how far along you are, and when your baby may be due.

There are several ways to pinpoint how old your baby may be. Here’s how to calculate gestational age manually:

  • Determine the first date of your last period
  • Add 280 days (40 weeks) to the first day of your last period

Many doctors will use this method to determine how far along you are, before moving onto an early ultrasound to determine gestational age. That’s because it’s difficult to see a tiny fetus prior to six weeks of pregnancy.

From there, doctors can measure the fetus to make a more estimated guess at your baby’s gestational age.

Determining how far along you are can become confusing based on different dating methods and terms used. Here’s how they differ:

  • Gestational age vs. conception date: Gestational age is commonly used by doctors to count the length of a pregnancy but doesn’t account for conception date. In most cases, gestational age counts from the first day of the last period, meaning it often includes two additional weeks prior to conception.
  • Gestational age vs. fetal age: While gestational age determines a due date based on your last period, fetal age can be determined through an ultrasound. Because fetuses under 13 weeks grow at similar rates, doctors can determine how old your baby is based on their measurements. During an ultrasound, doctors will refer to a gestational age chart (also called a fetal growth chart) compare your fetus’ size to the size of average fetuses at certain ages. This can provide a more accurate date that may line up with
  • conception.

Difficulties in Determining Gestational Age

In some instances, it can be difficult for you and your doctor to determine how far along your pregnancy may be without the help of an ultrasound. This can be the case if:

  • You have an unusual or abnormal cycle
  • You don’t have a cycle due to a health condition or as a side effect of medications (such as birth control)
  • You can’t remember the date of your last period

In these situations, a doctor may require an ultrasound to determine your gestational age.

How to Calculate Your Due Date

There are several ways you can calculate your EDD (estimated due date):

  • Using a due date calculator to count gestational age (280 days from the first day of your last period)
  • Using a due date calculator based off your likely fertile window (possible dates of conception)
  • Undergoing an ultrasound, where a doctor can determine your fetus’ age and potential birth date based on crown-to-rump fetal measurements

The best due date calculator, such as one from AmericanPregnancy.org, allows you to input information about your last period, your estimated ovulation window, potential due date, and more. This can help you get a more balanced idea of when your baby will be born.

Why is your calculated due date different from the one on your ultrasound?

Many pregnant women wonder, “Can an ultrasound determine a more accurate due date?” The answer is yes! That’s because ultrasounds prior to 13 weeks are strong indicators of a fetus’ age and can help you hone in on when you likely conceived. For that reason, a due date calculated off gestational age (which uses the first day of your last period) may not be as accurate as a due date determined from an ultrasound.

Can my due date change?

It is possible for a due date to change based on information from ultrasounds. Because ultrasounds give the best dating information when done before 13 weeks, doctors can use this to give a more accurate due date.

If you were given one date based on gestational age, it’s possible for this date to change after an ultrasound.

So, does late ovulation change due date? Since we generally can’t tell when ovulation occurred, most doctor’s won’t base your due date off your believed date of ovulation or conception. During an ultrasound, a doctor may determine that your baby is a bit smaller than other babies of similar suspected age, meaning you could have ovulated a bit later than expected.

In this case, they may choose to update your due date to match fetal measurements and age.

Giving birth before your due date: What does it mean?

Many women give birth before the due dates, for a variety of reasons. Just because your baby is born before their due date doesn’t mean that they’ll be premature.

In fact, only an estimated 5 percent of women give birth on their actual due date. While many OBGYNs want women to carry close to 40 weeks, babies are often born on their own schedule. It isn’t abnormal for a baby to be born anywhere from three weeks prior to their due date to two weeks after.

Symptoms in the First Few Weeks of Pregnancy

Many women don’t know that they’re pregnant until they miss their first or second period, yet others begin to experience symptoms very early on. If you believe you may have conceived, the probability of being pregnant increases if you are experiencing any of these common early pregnancy symptoms:

  • Fatigue and exhaustion
  • Unexplained mood swings and moodiness
  • Tender or swollen breasts
  • Nausea
  • Light spotting (often occurring around implantation) and cramping
  • Aversion to certain foods and smells
  • Frequent urge to urinate

Many women who experience these early pregnancy symptoms do so starting around four to five weeks from their last period.

How to Determine the Father by Conception Date

Sometimes, a woman becomes pregnant but isn’t quite sure who the father may be. In these cases, many women search for how to determine the father of a baby by conception date, but unfortunately, there’s no “who got me pregnant” calculator.

In these situations, where a woman is pregnant with two possible dads, it helps to get out a calendar. Knowing how to calculate how pregnant you are can also help you determine when you may have gotten pregnant:

  • Circle the first day of your last known period (this is day 1 of your cycle).
  • Count 11 days out from day 1, and mark; this date, for most women with a cycle between 28 and 32 days, is the beginning of their fertile window.
  • Now, count out 10 additional days from the first fertile day; this date is likely the last fertile day (the close of your fertile window).
  • Note any days that you had sex within this fertile window, and with which partner. This can give you a clue as to which partner may be the father.
  • You can also count forward from the date of your last period to determine how pregnant you are.

You can use this information going forward when you meet with a doctor or undergo an ultrasound to determine fetal age. While the calendar method and ultrasound can’t hone in on a specific day you became pregnant, it can be helpful at determining who the father may be.