The 3 Trimesters Of Pregnancy: The First Trimester

The trimesters of pregnancy are divided up into three stages which are marked by specific fetal developments. The first trimester spans from week one to the end of week 12 and is when layers of cells become an embryo, which is what your baby is called at this stage. Trimesters of pregnancy help women to understand the changes happening within their bodies and aid in understanding the development of their baby. 

The First Trimester Of Pregnancy

The three trimesters of pregnancy generally last around 40 weeks but can range from 37 to 42 weeks. Each trimester of pregnancy lasts 12-14 weeks and marks different changes to your baby and body. Here at Kernodle OB/GYN, we are committed to ensuring you understand your body as a woman and the three trimesters of pregnancy. For this specific blog, we are going to be focusing on the first trimester.

Trimester One

The first trimester of pregnancy begins on the first day of your last menstrual period, called the gestational age of pregnancy, and goes until the 13th week. During this trimester, your body goes through significant physical and emotional changes. Even if you don’t look or feel pregnant, your baby grows faster in the first trimester than in any other trimesters of pregnancy. 

Weeks One To Four

During the beginning of your pregnancy, the fertilized egg implants itself into the side of your uterus. Several important structures begin to form from a clump of cells during the first month of pregnancy, such as the nervous system, skeleton, organs, and skin. By week four, despite being the size of a poppy seed, your baby’s major organs, such as their lungs, brain, and heart, are already developing. 

Weeks Five To Eight

During the second month, you may begin to notice early signs of pregnancy as your hormones are working overtime. Tiny buds begin to form, which will grow into your baby’s arms and legs. During this time, fingers, toes, eyes, digestive tracts, and sensory organs begin to form, too. Some women begin to experience morning sickness at week six and can peak around week nine. By the end of week eight, your baby’s respiratory system is forming, and breathing tubes extend from your baby’s throat to its developing lungs. 

Weeks Nine To 12 

Your baby’s arms, hands, fingers, feet, and toes are fully formed in the third month of pregnancy. At this point, your baby’s reproductive organs develop, but it still can be difficult to distinguish sex through an ultrasound. At the end of the 12th week of pregnancy, the fetus is roughly 3 to 4 inches long and weighs around 1 ounce, and the placenta is fully formed. Although it is too early to feel your baby’s movement, just 12 weeks after your last period marks the time your fetus is fully formed. 

Trimester One Symptoms

The trimesters of pregnancy can bring on a whole host of symptoms as your body experiences increases in estrogen and progesterone. Many women experience the worst pregnancy symptoms during the first trimester. Some common symptoms include

  • Nausea (morning sickness)
  • Mood swings
  • Fatigue
  • Sore breasts or breast tenderness
  • Increased urge to urinate
  • Acne or other skin changes

Some symptoms that warrant a call to your doctor during the first trimester include heavy vaginal bleeding, severe abdominal pain, painful urination, and vision disturbances. 

This guide to the first trimester of pregnancy is a great first step in gaining a better understanding of your growing baby and body. Are you a woman who has questions about the trimesters of pregnancy? Kernodle OB/GYN is here to guide you through with full-scope individualized women’s health care, including gynecological care, midwifery services, and low- and high-risk maternity care for women and their families. Check out our website or give us a call for more information.

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