How do I calculate what week of pregnancy I am? Why is this important?

A normal pregnancy lasts 40 weeks, or 280 days or 9 calendar months. It is also considered the norm if the birth takes place 2 weeks earlier or later. The moment of the cycle when ovulation took place is not considered the beginning of pregnancy, as it is difficult to capture. Therefore, it was assumed to be the first day of the last menstrual period. A woman who has noted it down can calculate for herself what week and day of pregnancy she is.

What week of pregnancy am I according to my last period?

Pregnancy age is most often calculated according to the first day of the last menstrual period. This is the so-called. Naegele’s rule. It works especially well for women who have regular cycles of 28 days. However, it is worth remembering that such estimates are never 100% accurate. Therefore, a birth that takes place between 38 and 42 weeks of pregnancy is considered the norm.

A woman who has doubts about which week of pregnancy she is must consider when she had the first day of her last period. Then she should subtract 3 months from it and add a year and 7 days. If your cycles are irregular, you should still add or subtract the appropriate number of days. The same is true for pregnancy after IVF (however, 14 days must be subtracted from the day of the ovarian puncture when the cycle has been postponed).

It is important to remember that this is only a way to calculate the week of pregnancy and the expected date of delivery. The result is not the same as the age of the fetus, which is on average lower by about. 14 days. This is because the fusion of the sperm with the egg cell occurs later than the first day of the last menstrual period. The moment, however, is difficult to grasp. 

Read also: Baby’s movements at 21. Week of pregnancy – how often?

Week and day of pregnancy based on ultrasound

Pregnancy age can also be calculated using ultrasound (ultrasound). The doctor determines it based on the fetus’s parietal-seat length, known as CRL. However, this is done only in the first trimester (preferably around the 10th week of pregnancy). At later stages, the specialist takes into account the length of the femur, the bicoronal dimension of the fetal head or the transverse dimension of the cerebellum. Such a calculation of the week of pregnancy is possible only if the baby is developing normally. 

Other methods to calculate what week of pregnancy I am?

A mom-to-be who is wondering how to calculate what week she is pregnant can use online birth calculators. These are free tools that, after entering some data, present the result. It consists of the week, day, month and trimester of pregnancy and the expected date of delivery. However, in order for it to be correct, you need to know the date of the first day of your last period.

The gynecologist also estimates the age of pregnancy based on the height of the uterine fundus. This is possible because its location changes every few weeks. At 16 weeks it is 2 fingers above the pubic conjunctiva, but at 28 weeks of pregnancy it is already above the umbilicus. In some cases, a woman can also be asked when she felt the baby’s first movements.

Why is a week of pregnancy calculated?

Calculating the week of pregnancy is important because this will help you determine whether the pregnancy is progressing properly. It is also important in assessing the development of the fetus (e.g., it sometimes happens to be delayed). Knowing the week of pregnancy allows you to avoid unnecessary induction of labor or cesarean section, as well as correctly identify preterm labor or miscarriage and implement appropriate procedures to safeguard the health and life of the mother and her baby.

See also: 23 week of pregnancy – weight and positioning of the baby