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What Happens in the First Trimester of Pregnancy?

Sep 21, 2022

What is the 1st Trimester of Pregnancy?

The span of your last menstruation period (LMP) date till week 12, is called the first trimester of pregnancy. So you might be five to six weeks pregnant at the time when you confirm the pregnancy. 

Fertilization occurs once the sperm gets fused with the matured egg, the fertilized egg known as a Zygote. The zygote divides into tiny balls of cells known as a blastocyst that implants in the wall of a uterus, where it starts developing into an embryo and placenta. This embryo grows into a baby week by week.

First Trimester - Changes in Your Body

You may feel fatigued since your body is working hard to accept the process of developing an embryo into a fetus during your first trimester. Every pregnant woman will undergo common symptoms such as morning sickness, indigestion, constipation, breast tenderness, frequent urination, and food aversions. During pregnancy, there will be a spike in hormones level, and your muscles and bones become more flexible and stretch to accommodate your growing baby. But keep in mind that every pregnancy is different for every woman.

These changes may feel unpleasant, but still, your body knows the exact process to put up with safe pregnancy. This may settle down in your second trimester. Both your physical and mental health plays a vital role in pregnancy. 

Fetus Growth in the First Trimester

Your fetus is surrounded by the amniotic sac in the womb and this helps to grow throughout pregnancy. In the first trimester, the placenta develops and transfers nutrients to the baby from the mother.

Here are the highlights of fetus development happening in this sensational time

Blood vessels and Heart: 

The blood vessels and heart of the baby develop, and the heart starts to beat.


You’re in the 6th week of your pregnancy. The baby may develop rapidly this week. The neural tube supports the formation of the brain structures and the spinal cord. The body of your baby begins to appear on a C-shaped curve.

Arms and legs: 

During 8 weeks, the nostrils depressions may rise and become visible. The neck and its trunk begin to straighten. Retinas start to form this week, and the tiny buds arise that later grow into arms and legs.

Fingers and Toes:

At the end of the 10th week, the embryonic period is over, and now the embryo becomes a fetus. The head of your fetus becomes rounded. The webbing may disappear, and the fingers and toes grow longer. The eyelids continue to develop, and the ears begin to form as a little fold of skin. 


At 12 weeks of pregnancy, the fingernails get sprouted, and the intestines may form in the abdomen. The face of the baby has now taken its shape more like a human.

At the end of the first trimester, your fetus would be 2-4 inches long and approximately 20g in weight.

Weight Gain in the First Trimester

Gaining weight is the primary of a healthy pregnancy. Experts say a pregnant woman may gain weight in the first trimester, though some may lose weight due to morning sickness or other symptoms arising in this trimester.

Your doctor will monitor your weight from the beginning of your pregnancy to ensure you're in a healthy range of weight. It’s common to get averted to food during the first three months of pregnancy, still, you should eat a small quantity of nutrition-rich foods frequently to turn this condition better.

During pregnancy, it is necessary to avoid bacteria content or other toxin foods like undercooked meat, unpasteurized milk products, raw eggs, raw oysters, and fish that are high in mercury as these foods are unhealthy and cause harm to you and your fetus.


Related: Is it Safe to have an Intercourse During the First Trimester?

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Do's and Don'ts during the First Trimester of Pregnancy

During the exciting time of the first trimester, many pregnant mothers, particularly first-time mothers, may be unaware of their do's and dont's.

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