How Long Does 1St Trimester Last

What is the First Trimester of Pregnancy?

The first trimester of pregnancy spans the initial twelve weeks of pregnancy, typically happening between conception and the thirteenth week of gestation. During this time period, a host of physical and emotional changes occur as the body adapts to carry and nourish the baby. Many of the processes that will occur throughout the pregnancy begin during this period, as the mother’s body undergoes a dramatic process of change.

What Happens During the First Trimester?

The most significant physical transformation to occur during the first trimester is the development of the fetus. Usually, the fetus receives all of its nourishment from the mother’s bloodstream, and takes on its own vital systems, such as the respiratory and digestive systems. By week 6, the fetus can move its arms and legs, and by week 8 its skeleton and facial features are forming.

Most women will also experience a plethora of emotional and physical changes as their body adapts during the first trimester. These changes may include:

  • Morning sickness: Many women experience some degree of morning sickness, with symptoms such as nausea and vomiting.

  • Tender breasts: Swelling and tenderness of breasts are common during this time.
  • Fatigue: During the first trimester, many women experience debilitating fatigue, resulting in an inability to carry out daily tasks.
  • Food cravings: Food cravings are common during this period, with some women wanting strange combinations at odd times of day.
  • Mood swings: Pregnancy hormones can cause many women to experience mood swings and bouts of depression.

How Long Does the First Trimester Last?

The first trimester of pregnancy typically lasts for twelve weeks and ends when the mother reaches the thirteenth week of gestation. However, many experts and medical professionals measure the first trimester from the day of conception and thus it can last up to fourteen weeks and a few days, depending on the date of the mother’s last menstrual period.

Average Length of the First Trimester

The average length of the first trimester of pregnancy can be roughly broken down into the following:

  • Week 1 – 4: In this period, the egg travels down the fallopian tubes and implants in the uterus.
  • Week 5 – 6: The fetus begins to form, and begins to move its arms and legs.
  • Week 7 – 8: At this time, the skeleton and facial features are forming.
  • Week 9 – 12: In this period, the fetus begins to rapidly grow, and all of the organs and systems in the body are formed.


The first trimester of pregnancy lasts roughly twelve weeks, beginning on the date of conception and ending at the mother’s thirteenth week of pregnancy. During this time, the fetus is rapidly growing and developing, and the mother will experience a variety of physical and emotional changes as her body adjusts to pregnancy.

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