Pregnancy Calendar

Almost every woman who learns that she is expecting a baby asks herself: "What week am I pregnant?" What are the symptoms of pregnancy that can happen to me week after week and how do I deal with them? " Especially for all future mothers and their loved ones, we have prepared a pregnancy calendar in which the pregnancy is described in detail week by week. 

Thanks to this, future parents can more consciously go through this special time. Especially when they are expecting their first child and are not sure what the next weeks may bring. In our pregnancy calendar, we describe the most common pregnancy conditions and how to deal with them. We also advise on how to convert individual weeks of pregnancy into months and trimesters, and on which week of the pregnancy calendar are medical examinations recommended by the Polish Society of Gynecology and Obstetrics (PTGiP).

Week by Week Pregnancy Guide

On the Internet you can find many poorly reliable and incomplete sources about the course of pregnancy. That is why our articles have been prepared in cooperation with experienced doctors of the Institute of Mother and Child, specializing in issues in the field of gynecology and obstetrics. We have collected comprehensive data on each week of pregnancy, so that a pregnant woman will be able to better understand what is happening to her body, what are the symptoms of pregnancy week by week and how the baby in her belly develops. 

It is also worth getting acquainted with the pregnancy calendar for the coming weeks and months in advance. It will help even better mentally and practically prepare for the next stages of pregnancy and register in advance for the medical examinations recommended in the given weeks, which we always remind you of in our articles.

Pregnancy calendar: calculate which month, week and trimester it is, or how not to get lost in "pregnancy math" 

A physiological pregnancy lasts 9 months, which are divided into 3 trimesters (each consisting of 3 months). Due to the fact that pregnancy is an extremely dynamic period, in which important changes in the development of the fetus often occur from week to week, the entire pregnancy is divided into individual weeks in the medical nomenclature - this is why calendar physiological pregnancy covers 40 weeks (i.e. 9 months). Below is a table that clearly shows the division of the entire pregnancy into individual months, weeks and trimesters:


  • First trimester of pregnancy lasts from fertilization to 13,0 weeks of pregnancy (tc);
  • Second trimester starts at 13,1 weeks of pregnancy and lasts up to 27,0 tc;
  • Third trimester begins at 27,1 weeks of pregnancy. Term pregnancy is in the range of 37,0 - 41,6 tc

Pregnancy week after week: how to understand the system of marking the weeks of pregnancy?

In medical records and articles about pregnancy, you can often find a record of pregnancy weeks in the form of, for example, 11,3 tc What does the decimal point mean? Well, in the obstetric nomenclature, the age of pregnancy is marked in weeks. So 11,3 tc means that the exact age is 11 finished weeks and 3 days, so she is pregnant during the 12th week of pregnancy.

Days are entered from 0 to 6. Each new week is marked as “given week + 0 (zero) days” and the last day is shown as “week” + 6 days. There is no digit 7 in this entry. If a pregnant woman has heard from her gynecologist that she "changes" the week of pregnancy, e.g. on Mondays, it means that on each subsequent Monday, the age of pregnancy will be marked as "week" + 0, that is e.g. 16,0, 17 (beginning of week 16 because you turned XNUMX). Don't worry, in each of our pregnancy calendar articles you will find an explanation of which week of pregnancy falls in a given month and trimester. 

Pregnancy calendar: calculate the due date

The due date is usually calculated on the basis of the so-called Naegele rules, which states that:

"we calculate the due date on the basis of: the date of the first day of the last menstruation + 7 days - 3 months (90 days) + 1 year (365 days) "

Please note that this calculated due date may not be accurate. The rule assumes that all months are slightly more than 30 days (30,416 days), and this is not the case. In addition, the calculations are based on a regular cycle, i.e. one that always lasts 28 days and in which ovulation occurs exactly in the middle, i.e. on the 14th day. In fact, the length of the menstrual cycle and the occurrence of ovulation can vary from woman to woman, including: to individual conditions, existing diseases or lifestyle. A normal menstrual cycle lasts about 25 to 35 days and such fluctuations are natural. Finally, not all pregnancies are as long as 280 days as assumed by Naegele.

The due date can be calculated more precisely based on the modified Naegele rule, taking into account individual differences in the length of the menstrual cycle:

,, Date of the last menstrual period + 1year + 7 days-3 months +/- X days = due date

X is the number of days by which the cycle length differs in a given woman (if the cycle does not last 28 days) "

It is worth mentioning that the date of delivery is automatically set at 40,0 weeks, but the term pregnancy is in the range of 37,0 - 41,6 weeks. Often the patients are worried that they gave birth "prematurely", ie at 37,3 weeks. However, this is a completely physiological range and should not be of concern. Only about 40,0% of babies are born in “term of childbirth”, ie in 5 weeks of gestation.

What week of pregnancy am I in? Determining the age of pregnancy and the date of delivery by ultrasound

The age of pregnancy, and thus the estimated date of delivery, can be most accurately determined by performing an ultrasound examination at a gynecologist. In the first trimester of pregnancy, it is recommended that the ultrasound be performed up to 13,6 weeks of pregnancy, but not earlier than 5-7 weeks of pregnancy. Only then, based on the child's development stage, is it possible to accurately determine the pregnancy age. The doctor then measures the parietal-seat length, i.e. CRL - Crown-rump length (from the top of the head to the lower border of the fetal buttocks).

What week of pregnancy am I? The gynecologist can most accurately answer this question up to 14,2 tc (i.e. the maximum CRL measurement equal to 84 mm). After this date, each fetus begins to develop at an individual pace, conditioned by, inter alia, genetic or environmental factors.

The date of delivery calculated from the last menstruation is changed to the date of delivery calculated from the ultrasound if:

- the difference is more than 5 days with an ultrasound performed before the 9th week of pregnancy

- the difference is more than 7 days with the ultrasound performed between 9,0-15,6 tc

Is it worth keeping your own pregnancy calendar?

There are many situations where a pregnancy calendar note can prove very useful. In order to assess obstetric risks, a lot of information may be needed from the period preceding the pregnancy, as well as from the incipient stages. Sometimes it is difficult to recall them from memory, but it is easy to go back to notes about symptoms, well-being or unusual situations

When trying for a baby, it is also worth scrupulously writing down the date of each last menstruation in your calendar. As a result, the age of pregnancy and the estimated date of delivery will be less likely to be miscalculated. The precise date of the last menstruation also makes it possible to calculate the fertilization date with an accuracy of 1-2 days (which is not clinically significant in the case of natural fertilization, but is important when using the in vitro method). Moreover, such a gynecological pregnancy calendar, taking into account the date of the last menstruation, will help to more precisely determine the date of specialist prenatal examinations, including ultrasound of the 1st trimester, which must be performed within a strict time frame.

A pregnancy calendar in a traditional form, or maybe an application for the phone?

A personal pregnancy calendar can be kept in a regular notebook in the form of a diary or you can use ready-made pregnancy notebooks for expectant mothers. Special applications-pregnancy calendars, which can be installed on the phone and always at hand, are also very popular. 

When using ready-made pregnancy applications, it is worth remembering that most of them are translated from English, which may cause some inaccuracies. In addition, not all of them take into account the recommendations of the Polish Society of Gynecology and Obstetrics, thus failing to meet the medical standards in force in Poland. When using these helpful pregnancy applications, it is always worth remembering that none of them will replace the professional advice of a gynecologist, midwife or other specialist, to whom it is worth addressing all your questions and reporting any worrying pregnancy symptoms.

Regardless of the form you choose, we invite you to familiarize yourself with our pregnancy calendar, which will certainly prove to be a knowledge-rich support and an invaluable companion for the upcoming, exceptional weeks.

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