How to find out in which week of pregnancy I am. Write down the first day of the last menstrual period, from which the beginning of pregnancy is calculated

How to find out in which week of pregnancy I am. Write down the first day of the last menstrual period, from which the beginning of pregnancy is calculated
A pregnancy test will confirm (or deny) pregnancy, but it will not tell you in which week you are pregnant. Only a gynecologist can safely determine this. If you don't want to wait for a doctor's visit, you can calculate the approximate length of pregnancy yourself. However, for this you need to know the first day of your last period, because the beginning of pregnancy is calculated from it. Yes, the moment when you are not yet pregnant is considered the beginning of pregnancy.

When is your due date? is a question you will be asked about a million times in the coming months, not only from family and friends, but also from strangers. Gynecologist Alyssa Dwecková points out that knowing the estimated due date (= estimated due date, EDD) is useful not only for family visits, but especially for conversations with the doctor, who accordingly plans gynecological examinations and makes specific medical decisions. (1) "You will find out the EDD at the first pregnancy check-up. If you don't want to wait that long, use an online calculator that can be surprisingly useful," Dweck adds.

Why is EDD so important? It is part of essential prenatal care

The date of birth is a key part of prenatal care. "It determines which week or month of pregnancy you are in, thereby letting the medical team know when and which blood tests, ultrasounds and other examinations you need to undergo," says Dr. Noopur Ghadeova. (1) (2) Although the date of birth can almost never be predicted exactly, it provides the necessary estimate of the child's arrival in the world. Abroad, instead of "expected date of birth", the term "estimated date of birth" is preferred.

"Babies are naturally born roughly between 37 and 42 weeks, which is the period we refer to as the due date, when the baby has reached full health and maturity and is ready to be brought into the world," says Professor Jason Gardosi of the Perinatal Institute (3) and complements his claims with interesting statistics:

  • Up to 60% of babies are born roughly a week before or after EDD.
  • More than 90% of babies are born two weeks before or after the EDD.
  • Only 4% of babies are born exactly on the EDD (this means that the probability that the doctor will hit on the exact day is only 1:20). (3) (4)

Pregnancy calculator: How it works and when, according to it, you will find out that you are pregnant

The pregnancy calculator is used to calculate the week of pregnancy in two basic ways: either by the date of the last period or by the date of conception. (3) We will now take a closer look at both methods.

Calculation of pregnancy according to the date of the last menstrual period (LMP)

Knowing the date of the first day of the last menstrual period (= last menstrual period, LMP) will help you calculate the estimated due date. Indeed, studies confirm that the exact determination of LMP is the most beneficial for estimating the due date. (5) However, there is one small catch. "The EDD calculation based on the date of the last period relies on the fact that the woman has regular menstrual cycles," says Dr. Salena Zanotti of the Cleveland Clinic.

The average cycle length is 28 days, with ovulation occurring on the 14th day of the cycle. This means that there is a wide time interval in which menstruation can occur. "We consider a period to be regular if it occurs every 24 to 38 days, with ovulation usually occurring 14 days before the arrival of the next period," add experts from OASH, Office of the Assistant Secretary for Health. (6)

If your period comes earlier or later than the mentioned time interval, or if it comes at an unpredictable time each month, it can be considered irregular. Although irregular periods are common, they significantly affect the accuracy of the pregnancy calculator. To find out which week of pregnancy you are in, enter the number of weeks since the first day of your last period into the calculator. If it started e.g. March 4th and today is April 16th, you are 6 weeks pregnant. (7)

Calculation of pregnancy by date of conception

Some online pregnancy calculators can calculate EDD based on conception date. It is likely that if you had problems conceiving, you had your AMH level tested and since then you have tracked your fertile days. You probably already have experience with the ovulation calculator and basal body temperature measurement, so calculating the EDD according to the pregnancy calculator is just a kind of icing on the cake.

However, not every woman knows the exact date of conception, especially if she does not track ovulation. It is also important to note that the date of conception is not necessarily the same day you had sex. Sperm in the female reproductive system survive up to 5 days; the egg is viable for 12 to 24 hours, which means that you will find out the pregnancy after a different time than the one you wrote down in the diary. (8) However, if you know the exact date of conception, nothing is easier than entering it into the pregnancy calculator. If you know that conception took place e.g. On April 1st, you are 4 weeks and 1 day pregnant and your EDD is December 23, 2024.

Do you want to be 100% sure in which week of pregnancy you are? Get the gestational age of the fetus calculated

If you want 100% certainty regarding the length of pregnancy, have the gestational age of the fetus calculated. April L. Winningham from Encyclopedia Britannica states that "gestational age is the period during which the fetus is growing in the mother's womb." (9) On the maminkám.cz website it is written: "The correctness of the EDD is verified by age estimation according to the measurement of the length of the fetus during an ultrasound examination. It is based on the value of CRL (Crown-Rump Length), i.e. the length of the fetus from crown to coccyx." (10)

This information is especially useful in the early stages of pregnancy, because after the 24th week, ultrasound is much less accurate in predicting the gestational age of the fetus. (11) CRL is measured from 6 or 7 to 15 weeks of pregnancy. The website maminkám.cz warns that only measurements performed between the 8th and 15th weeks of pregnancy can be used to determine the gestational age of the fetus, while the most accurate results are provided by measurements between the 11th and 15th weeks of pregnancy. (10)

Do you need to find out which week of pregnancy you are in and do you have a gynecological examination scheduled for a long time? Use an online pregnancy calculator that works by entering the first day of your last period or conception date. To estimate the due date, you only need to know one date.

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Sources

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  2. Profile | Tufts Medicine. (n.d.). Online. Dostupné z: https://www.tuftsmedicine.org/doctor/noopur-ghade. [cit. 2024-04-17]. 
  3. Moore, B. K. (2015). How accurate are “due dates”? BBC News. Online. Dostupné z: https://www.bbc.com/news/magazine-31046144. [cit. 2024-04-17]. 
  4. Bras, C. L. (2013). How to calculate your pregnancy due date in France. French Mamma. Online. Dostupné z: http://frenchmamma.com/2011/07/25/how-to-calculate-your-pregnancy-due-date-in-france/.  
  5. Edwards, K. I., & Itzhak, P. (2019). Estimated date of delivery. Online. Dostupné z: https://www.ncbi.nlm.nih.gov/books/NBK536986/. [cit. 2024-04-17]. 
  6. Your menstrual cycle | Office on Women’s Health. (n.d.). (2021). Online. Dostupné z: https://www.womenshealth.gov/menstrual-cycle/your-menstrual-cycle. [cit. 2024-04-17]. 
  7. Website, N. (2021). Due date calculator. nhs.uk. Online. Dostupné z: https://www.nhs.uk/pregnancy/finding-out/due-date-calculator/. [cit. 2024-04-17]. 
  8. Pregnancy - identifying fertile days: MedlinePlus Medical Encyclopedia. (n.d.). (2022). Online. Dostupné z: https://medlineplus.gov/ency/article/007015.htm. [cit. 2024-04-17]. 
  9. Winningham, A. L. (2016). Gestational age | Definition & Stages. Encyclopedia Britannica. Online. Dostupné z: https://www.britannica.com/science/gestational-age. [cit. 2024-04-17]. 
  10.  Jak se počítají týdny těhotenství | Maminkám.cz. (n.d.). Online. Dostupné z: https://www.maminkam.cz/jak-se-pocitaji-tydny-tehotenstvi. [cit. 2024-04-17]. 
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