Podsumowując:
- 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'll often see gestational weeks written as, for example, 11,3 weeks. What does the number after the decimal point mean? In obstetrics, gestational age is measured in completed weeks . So, 11,3 weeks means the exact age is 11 completed weeks and 3 days, meaning the pregnant woman is in her 12th week of pregnancy.
Days are given in notation from 0 to 6. Each new week is marked as "given week + 0 (zero) days," and the last day is marked as "week" + 6 days. This notation does not include the number 7. If a pregnant woman has been told by her gynecologist that she "changes" the week of pregnancy, for example, on Mondays, this means that on each subsequent Monday, the gestational age will be marked as "week" + 0, i.e., 16,0 (the beginning of week 17, since you've turned 16). Don't worry, each of our pregnancy calendar articles will explain which week of pregnancy falls in which month and trimester.
Pregnancy calendar: calculate the due date
The due date is usually calculated based on Naegele's rule, which states that:
" the due date is calculated based on: the date of the first day of the last menstrual period + 7 days – 3 months (90 days) + 1 year (365 days)"
It's important to remember that the due date calculated this way may be inaccurate. The rule assumes that all months have just over 30 days (30,416 days), which is not the case. Furthermore, the calculations are based on a regular cycle, meaning one that always lasts 28 days and in which ovulation occurs exactly halfway through, on day 14. In reality, the length of the menstrual cycle and the occurrence of ovulation can vary for each woman, due to factors such as individual circumstances, medical conditions, and lifestyle. A normal menstrual cycle lasts approximately 25 to 35 days, and such fluctuations are natural. Finally, not every pregnancy lasts exactly 280 days, as in Naegele's assumptions.
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's worth mentioning that the due date is automatically set at 40,0 weeks, but a full-term pregnancy falls between 37,0 and 41,6 weeks. Patients are often concerned that they gave birth "prematurely," for example, at 37,3 weeks. However, this is a perfectly normal range and shouldn't cause concern. Only about 5% of babies are born at "due date," meaning at 40,0 weeks.
What week of pregnancy am I in? Determining the age of pregnancy and the date of delivery by ultrasound
Gestational age, and therefore the estimated due date, can be most accurately determined by an ultrasound examination performed by a gynecologist. In the first trimester, ultrasound is recommended by 13,6 weeks of pregnancy, but not earlier than 5-7 weeks. Only then, based on the fetal developmental stage, can the gestational age be determined with sufficient precision. The doctor then measures the crown -rump length (CRL) (from the top of the head to the bottom of the fetal buttocks).
How many weeks pregnant am I? A gynecologist can provide the most accurate answer to this question up to 14,2 weeks gestation (i.e., a maximum CRL measurement of 84 mm). After this date, each fetus begins to develop at an individual pace, determined by factors including genetic and 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 in which notes from a pregnancy diary can prove very useful. To assess obstetric risk, you may need a range of information from before or during the early stages of pregnancy. While it can be difficult to recall these details, it's easy to refer back to notes about symptoms, well-being, or unusual situations.
When trying to conceive, it's also worth carefully noting the date of each last menstrual period in your calendar. This will reduce the likelihood of errors in calculating gestational age and estimated due date. A precise date of your last menstrual period also allows for calculating the date of conception to within 1-2 days (which is clinically insignificant in natural conception, but is important when using in vitro fertilization). Furthermore, such a gynecological pregnancy calendar, taking into account the date of your last menstrual period, will help you more precisely schedule specialized prenatal tests, including first-trimester ultrasounds, which must be performed within a strict timeframe.
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 pre-made pregnancy apps, it's important to remember that most are translated from English, which may cause some inaccuracies. Furthermore, not all of them follow the recommendations of the Polish Society of Gynecology and Obstetrics, thus failing to meet medical standards in Poland. When using these helpful pregnancy apps, it's always worth remembering that none of them replaces the professional advice of a gynecologist, midwife, or other specialist, to whom you should first direct all your questions and report any concerns about pregnancy.
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.
