How to calculate the weeks of pregnancy and due date?

If you have recently discovered that you have become pregnant and have not yet had time to visit the doctor, surely the first thing you are wondering is when your baby will be born. According to several studies, only 1 in 20 babies is born on the exact due date that had been calculated. Most babies are usually born within two weeks before or after 40 weeks of pregnancy on average . Therefore, although you can try to calculate the approximate date, it is most likely that you will not guess exactly when the baby is going to be born until the day of delivery. Anyway, if you want to calculate the weeks of pregnancy to get an idea, in this article we tell you how to do it.

How can the approximate due date be calculated?

Most pregnancies last about 40 weeks (or 38 weeks from conception), so the best way to estimate your due date is to calculate the weeks of your pregnancy, counting 40 weeks from the start of your last menstrual period . That is, subtracting 3 months from the first day of your last menstrual period (LMP), and then adding 7 days: that will be the expected date for you to leave your accounts the following year. For example, let’s say you had your last period on April 11. Then you must count back 3 months (which brings you to January 11), and then add 7 days: The expected due date in this case would be January 18.

Is this way of calculating the weeks of pregnancy effective?

This is how doctors do it and, although it is usually a fairly accurate criterion, it is not an exact science, so there is a margin of between one and two weeks before and after the established date to consider that the delivery falls within to expected date.

Calcular las semanas de embarazo

However, it should be noted that this system for calculating the weeks of pregnancy works well for women who have a regular menstrual cycle. But if your cycle is irregular, this method may not be accurate . In these cases, try to determine precisely when conception occurred in order to help estimate the due date. To do this, there are some additional parameters that your doctor can use when calculating the weeks of pregnancy you are in and the weeks you have left. These parameters are:

  • The size of your uterus, which will be seen when your initial internal pregnancy exam is done.
  • An early ultrasound ultrasound, which is used to see what stage of pregnancy you are in based on the development of the fetus.
  • Pregnancy milestones, such as hearing the fetal heartbeat for the first time (around week 9 to week 12 of pregnancy) and the sensation of fetal movement (between 16 weeks and 22 weeks)
  • The height of your fundus or the top of your uterus – The fundus should reach your belly button around week 20, which helps confirm your due date.

Can my due date change?

Although not a cause for concern, your doctor may change your due date long after calculating your weeks of pregnancy for various reasons as your pregnancy progresses , such as if you have abnormal uterine height or have alpha-fetoprotein levels ( a protein produced by the baby) abnormal. These changes are within normality, and will generally be between one or two weeks before or after the date initially planned.