Why Pregnancy Is Counted From The Last Menstrual Period
Pregnancy is counted from a women’s last menstrual period because the start of a period is easily observable and usually known to a woman whereas the date of conception is much less likely to be known.
Historically, the first day of the last menstrual period became the date from which pregnancy is counted even though conception occurs about two weeks later.
The LMP formula is good for working out an initial age of pregnancy but ultrasound is more accurate. The age of pregnancy may be revised following your ultrasound scan.
Why Pregnancy Calculators Can Only Estimate
There are few reasons to explore about why pregnancy calculators can only provide your babys estimated birth date:
Pregnancy Term & Due Date
Pregnancy is a term used to describe a woman’s state over a time period during which one or more offspring develops inside of a woman. Childbirth usually occurs approximately 38 weeks after conception, or about 40 weeks after the last menstrual period. The World Health Organization defines a normal pregnancy term to last between 37 and 42 weeks. During a person’s first OB-GYN visit, the doctor will usually provide an estimated date at which the child will be born, or due date. Alternatively, the due date can also be estimated based on a person’s last menstrual period.
While the due date can be estimated, the actual length of pregnancy depends on various factors, including age, length of previous pregnancies, and weight of the mother at birth.1 However, there are still more factors affecting natural variation in pregnancy terms that are not well understood. Studies have shown that fewer than 4% of births occur on the exact due date, 60% occur within a week of the due date, and almost 90% occur within two weeks of the due date.2 As such, while it is possible to be fairly confident that a person’s child will be born within about two weeks of the due date, it is currently not possible to predict the exact day of birth with certainty.
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When Did I Conceive
Are you pregnant but not sure exactly when you conceived? An ultrasound is the most accurate way to determine how far along your pregnancy is. Ultrasound exams provide images and include various measurements of your developing baby that can help estimate how many weeks pregnant you are and your approximate conception date. If you are making a pregnancy decision and want to learn more about your pregnancy and your options, call to see if you qualify for a free ultrasound.
Due Date Calculator
Please select the first day of you last period
You last period date:
Can My Due Date Change
Yes, your due date can change. While its definitely not a reason to worry, your doctor may change your due date for a number of reasons as your pregnancy progresses.
It may be that you have irregular periods and your early ultrasound dating was off, or that your first ultrasound was in the second trimester.
It could also be because your fundal height is abnormal, or your levels of alpha-fetoprotein , a protein made by the baby, are outside the usual range. Talk to your practitioner if you have any questions or concerns.
Accuracy Of Due Date Estimations
As mentioned above, not all pregnancies are delivered on their given due date. Because were talking about a human life developing here, dates and milestones are often estimates based on averages and estimates of a babys development.
You may find this shocking according to the CDC:
- About 57% of deliveries take place between 39- and 40-weeks gestation
Whats so shocking about this?
To break this down further, that means each day has roughly a 4-5% chance of being the date of delivery. Because due dates are estimates based on the first day of the last period, that means only about 5% of babies arrive on their exact due date.
This doesnt mean a pregnancy calculator isnt helpful in preparing you for the unexpected.
But the question still stands: why are due date estimations only estimations?
What Is My Due Date
Your due date, also known as your estimated date of delivery, is the approximate date your labor might begin. Your estimated due date is commonly calculated by adding 280 days to the date of the first day of your last period, using Naegeles rule. This may vary if you have irregular periods.
It’s worth noting that although predicted due dates are commonly calculated at 280 days, a baby is born on its predicted due date just 4% of the time. . A 2020 study published in the International Journal of Obstetrics & Gynaecology suggests a number of factors that can influence the length of your pregnancy, including ethnicity, height, variations in the menstrual cycle, the timing of ovulation, parity and maternal weight. It is for this reason that calculations using Naegeles rule can be considered as an estimate and not a definitive date.
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What Are The Chances Of Delivering On My Due Date
Just four percent. The due date isan estimate, says Scurfield. There are all sorts of factors that go into when a woman delivers. It may have to do with the size of the fetus or the health of the mother. Some women will have one baby early and the next baby late. Its nice to be able to predict and plan, but babies come when theyre ready.
I Know My Lmp Do I Need A Dating Ultrasound
Nope! You can rely on the due date suggested by your last menstrual period, but your healthcare provider may schedule one anyway. Your doctor may do it for other reasons, but for figuring out dates, its really not necessary if she isnt concerned and theres nothing odd happening, says Scurfield.
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How Can I Calculate Important Week
This pregnancy calculator helps you find out exactly how many weeks pregnant you are right now, details your baby’s development, and precisely what is happening to your body at the moment. Just enter your pregnancy due date or other information to create and calculate a personalized weekly and daily pregnancy calendar. The babyMed Monthly Pregnancy Calculator and Calendar is a week-by-week pregnancy calculator and calendar with information for each day of your pregnancy.
Pregnancy Calculator: How Is Your Due Date Calculated
While itâs true that most pregnancies last 40 weeks, there are other factors at play which will determine your due date. Most expectant mothers donât realize that both menstrual and ovulation periods count as the first two weeks of pregnancy. Many wonât be aware of their pregnancy until their first missed period, and by that time they could be up to five weeks in. That means that simply estimating nine months from the day you take a pregnancy test isnât going to calculate your due date, and, even so, factoring in a few weeks here and there for ovulation wonât either.
Unless you can pinpoint exactly what point of your ovulation cycle you were in at the time of fertilization, itâs difficult to know how far along you are and what date youâll meet your baby. Luckily, our due date calculator can help.
Using both the date of your last period and the length of your regular cycle, or exact date of conception, our due date calculator will quickly work out your estimated due date, tailoring it accordingly for longer, shorter, and average cycle lengths.
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Free Pregnancy Tests And Resources
If youre not sure if youre pregnant, not sure how far along you are, or have other questions about pregnancy and your options, call or visit Pregnancy Support Center of Roanoke Rapids. Were conveniently located on East 10th Street in the Forest Hill shopping center. Call to schedule your appointment or walk in during our office hours. All services are free and confidential.
When Will My Baby Be Born
This pregnancy calculator uses one of two methods to work out when your baby might be born. If you fill in the start date of your last period, it takes that date and adds 40 weeks . If you’ve chosen a different cycle, it will add or subtract days based upon that. If you choose to calculate by ultrasound date, the calculator will work out your due date based upon how far along you are on that date. This will likely yield a more accurate result.
The 280 day figure is based upon Naegeles Rule and is the most common method of calculating due dates. German obstetrician Franz Naegele created his formula in 1812 and it has been referenced ever since.
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How Are The Weeks Of Pregnancy Calculated
The 40 weeks of pregnancy begin on the first day of your last menstrual period.
This can be a little confusing because, for most people, conception doesnt occur until day 14 of the menstrual cycle. So yes, you arent actually pregnant during those first two weeks of pregnancy.
Modern data suggests that women have their babies a few days after their due date on average. Studies like this one found that Naegeles rule consistently places the due date about 2-4 days too early. So a better estimate may be 40 weeks and 3 days from LMP.
Alternatively, you can use our Advanced Due Date Calculator, which uses the Mittendorf-Williams rule to calculate your due date, which has been shown to be more accurate.
Dating Pregnancy Using Ultrasound
Ultrasound in the first trimester is the most accurate method of dating pregnancy. During the scan, baby is measured and the age of pregnancy is estimated by comparing baby’s size against recorded averages. If there is a significant difference between gestational age according to LMP and gestational age according to the ultrasound, you may be given a new gestational age and due date based on the ultrasound measurements.
Your pregnancy may also be dated by ultrasound measurement if an LMP formula was not appropriate for your pregnancy for any reason. LMP formulas are not suitable in several situations including the following: LMP is not known or is not certain, birth control pills were taken in the two months before LMP, the menstrual cycle is irregular, you are carrying multiples .
Although the age of pregnancy based on ultrasound measurements is more accurate than the age of pregnancy based on LMP, both are estimates and not definitive statements.
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How Accurate Is The Due Date
The pregnancy calculator gives you an approximate due date, which it works out your due date by adding 280 days to the first day of your last menstrual period . Your period and ovulation are counted as the first two weeks of pregnancy. If you have the baby on your due date, your baby has been growing for 38 weeks, not 40, but you are still classed as 40 weeks pregnant.
Development Scan / Gender Scan
The second ultrasound is usually between 18 to 20 weeks and helps your doctor determine if your baby is developing typically. This ultrasound will probably be your most thorough checkup.
Your doctor or midwife will check your babys organs such as the heart, brain, spine, abdomen, kidneys, and liver.
They will also check your babys head, face, limbs and count your babys toes and fingers. Using the ultrasound, your doctor or midwife can measure the amniotic fluid and check the placenta.
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First Day Of Last Period
Most pregnancies last around 40 weeks , so typically the best way to estimate your due date is to count 40 weeks, or 280 days, from the first day of your last menstrual period .
Another way to do it is to subtract three months from the first day of your last period and add seven days. So if your last period started on April 11, you’d count back three months to January 11 and then add seven days, which means your due date would be January 18.
This is how your doctor will estimate your due date and its a pretty solid target. But remember: Its just as normal to deliver a week or two before or after.
Convert Weeks Into Months How Does This Work
The Weeks into Months Pregnancy Calculator converts the amount of time youve been pregnant from weeks into the equivalent number of months. If you want to find out how far along into your pregnancy you are, the Weeks into Months Converter is the most efficient tool for calculating and recording your pregnancy.
To use the Weeks into Months Pregnancy Converter, simply fill in the required fields of the Pregnancy Calculator with the length of your pregnancy in weeks. Once youve pressed the calculate button, youll immediately be shown how far along you are in months!
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# 28 And 29 Weeks Pregnant
Your babys senses continue to develop. Around this time your baby might be able to tell the difference between your voice and your partners voice.
As her hearing continues to develop shell be able to hear higher pitched sounds and sounds from outside the womb.
Your baby is about the size of lovely butternut squash.
He or she weighs about 2 1/2 pounds and is about 15 inches long.
Your babys hair is growing well, and his or her head is growing bigger to accommodate a growing brain.
To keep up with the growing nutritional needs of your baby, eat foods with plenty of protein, calcium, folic acid, iron, and vitamin C.
Calculate Using A Pregnancy Test With Weeks Indicator
All pregnancy tests are designed to detect the pregnancy hormone human chorionic gonadotropin in urine, but some pricier tests offer a weeks indicator that promises to tell how far along you are. Unfortunately, these tests are pretty vague, stating only one to two weeks, two to three weeks or three-plus weeks pregnant. In addition, the tests measure from implantation, not from your LMP. A test might say that youre one to two weeks pregnant but youre actually four weeks pregnant, according to standard pregnancy calculations.
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Whats Happening To Your Immune System
You might be catching more colds than normal, as your immune system is slightly impaired while pregnant.
While the common cold isnt an issue for little bubs, other infections can cause problems for unborn babies .
Try to avoid people with these viruses while pregnant.
Unfortunately for me, I was plagued with a cold the entire time coupled with 3 sinus infections!
I am sure the reason was from the work environment I was in being around chemicals and such
I Had Sex Two Weeks Ago But My Doctor Says That Im Four Weeks Pregnant How
88 things nobody tells you about being pregnantIf you have a standard 28-day period, you will likely ovulate around day 14 and are most fertile around days 12, 13 and 14when you had sex to conceive. It takes about nine days after ovulation for implantation to occur, which brings you to around day 23. It takes a few days for your pregnancy hormone levels to be detectable by a pregnancy test, bringing you to around day 28. How far along you are in your pregnancy isnt calculated from conception or implantation but from the first day of your last normal period. If you had your period four weeks ago, then ovulated and had sex two weeks ago to become pregnant, youre currently four weeks pregnant.
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How Far Along Am I Four Ways To Figure Out How Pregnant You Are
Youre itching to know when your little one will arrive. Heres how to calculate how far you are in your pregnancy.
Its a question youll hear over and over until youre holding a baby in your arms: When are you due? Everyone wants to know that magic date, and youre probably more than a little curious about how far along you are, too. Your due date may become a beacon or a deadline , but its important to remember that your due date will only ever be an estimate of the week youll give birth .
That said, theres one big reason why an accurate estimate is important: in case of complications. If a woman goes into labour early, then we really want to know how far along she is, as best as we can tell, says Carol Scurfield, medical director of the Womens Health Clinic in Winnipeg. A week can make a big difference as far as the health of the baby is concerned.
Do your best to calculate your due date as soon as you discover youre pregnant. Heres how to do it.
Calculate Using Your Last Menstrual Period
The formula for calculating how far along you are is simply the number of days since the first day of your last menstrual period divided by seven:
Days since start of LMP ÷ 7 = # of weeks pregnant
Wondering how to calculate your number of months pregnant?
Days since start of LMP ÷ 30 = # of months pregnant
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