How to calculate pregnancy in weeks, months and trimesters?

Are you in week 10 or 12? Your second trimester or your third? Figuring out where exactly you are during your pregnancy is very important. However, pregnancy math can get confusing in general as week one of your pregnancy will start on the first day of your last menstrual period.

How many weeks is a full-length pregnancy?

Starting from the first day of your last menstrual period there are about 280 days or 40 weeks in a pregnancy. However, a full-term pregnancy is considered anywhere from 39 to 41 weeks long as not all pregnancies will exactly reach 40 weeks.

Image by Igor Link from Pixabay

A preterm or premature baby is delivered before 37 weeks of your pregnancy, existing different sub-categories of preterm birth, based on gestational age:

  • Extremely preterm (23 to 28 weeks)
  • Moderately preterm (29 to 33 weeks)
  • Late preterm (34 and 37 weeks)

Therefore, induction or caesarean birth should not be planned before 39 completed weeks unless medically indicated.

What is a trimester during pregnancy?

A normal pregnancy is divided into three different stages, called trimesters:

  • First trimester: the first trimester lasts from the very beginning of your pregnancy until you are 13 weeks plus 6 days pregnant.
  • Second trimester: the second trimester lasts from when you are 14 weeks to 27 weeks plus 6 days pregnant.
  • Third trimester: the third and final trimester last from you are 27 weeks pregnant until you give birth.

How many weeks pregnant is a month?

In the following chart you can check how the weeks, months, and trimesters of pregnancy line up with each other:

What happens during each week of pregnancy?

Find out what to expect during each week of pregnancy:

First trimester:

  • 1 week pregnant: Symptoms and what to expect
  • 2 weeks pregnant: Symptoms and what to expect
  • 3 weeks pregnant: symptoms, ultrasound and baby growth
  • 4 weeks pregnant: Placenta and embryo begin forming
  • 5 weeks
  • 6 weeks
  • 7 weeks
  • 8 weeks
  • 9 weeks
  • 10 weeks
  • 11 weeks
  • 12 weeks
  • 13 weeks

Second trimester:

  • 14 weeks
  • 15 weeks
  • 16 weeks
  • 17 weeks
  • 18 weeks
  • 19 weeks
  • 20 weeks
  • 21 weeks
  • 22 weeks
  • 23 weeks
  • 24 weeks
  • 25 weeks
  • 26 weeks

Third trimester:

  • 27 weeks
  • 28 weeks
  • 29 weeks
  • 30 weeks
  • 31 weeks
  • 32 weeks
  • 33 weeks
  • 34 weeks
  • 35 weeks
  • 36 week
  • 37 weeks
  • 38 weeks
  • 39 weeks
  • 40 weeks

References: WHO

Featured Image: Designed by macrovector / Freepik

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