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First Trimester: What Happens During The First 13 Weeks?

The first trimester is the first 12 weeks or 3 months of pregnancy period during which body may experience several changes.

The first trimester of pregnancy is critical as it is the stage where your baby’s major organs and body systems develop. It is important to have regular prenatal care during this period to ensure the health and well-being of both the mother and the developing fetus.

Proper nutrition, rest, and exercise are also crucial to support the baby’s growth and development and to avoid common complications such as gestational diabetes and hypertension.

These complications can occur during the first trimester and may have long-term effects on the baby if not treated accordingly.

It is essential to work closely with your healthcare provider and follow their recommendations to ensure a safe and healthy pregnancy.

Pregnancy can be divided into 3 main timeframes each containing 12 weeks.

During the first trimester, many important changes take place in the mother’s body, including hormonal changes, increased blood volume, and changes in the size and position of the uterus.

These changes can cause symptoms such as fatigue, morning sickness, breast tenderness, and frequent urination.

The first trimester is also a critical period for fetal development. It’s important to take care of yourself during the first trimester, eat a healthy diet, and avoid smoking, alcohol, and certain medications that may be harmful to the developing fetus.

Body Changes During the First Trimester of Pregnancy

The first trimester is a period of significant changes for both the mother and developing fetus. Here are some common body changes that occur during the first trimester of pregnancy:

Breast Changes

The breasts may become tender, swollen, and sore as the body prepares for breastfeeding.

Mood Swings

Hormonal changes during pregnancy can cause mood swings, including irritability, anxiety, and depression.

Increased Urination

The uterus expands during pregnancy, putting pressure on the bladder and causing more frequent urination.

Food Aversions and Cravings

Many women experience changes in appetite during the first trimester, including food aversions and cravings.


Hormonal changes can slow down digestion, leading to constipation.

Spotting or Cramping

Some women may experience spotting or cramping during the first trimester, which can be a sign of implantation or a potential complication.

Overall, the first trimester of pregnancy is a time of significant changes for both the mother and developing fetus. It is important to seek medical care and advice from a healthcare provider to ensure a healthy pregnancy.

The Symptoms of First Trimester

Here are some common symptoms that women may experience during the first trimester of pregnancy:


Many women experience fatigue during the first trimester as the body works to support the growing fetus.

Nausea and Vomiting

Morning sickness is a common symptom of pregnancy, affecting up to 80% of women. It is typically caused by the hormonal changes in the body and often subsides by the end of the first trimester.

Missed Period

The first sign of pregnancy is typically a missed period, which is caused by the fertilized egg implanting in the uterus.


Headaches are common during the first trimester due to hormonal changes and increased blood volume.

Dizziness or Light-headedness

Low blood pressure and changes in blood sugar levels can cause dizziness or light-headedness during the first trimester.

Dos and Don’ts of the First Trimester

There are some important items that need proper attention of the pregnant woman. Some must be done and some must not. Here they are:

What to Do

Remember to add the following to your routine:

  • Take required prenatal vitamins.

  • Eat a variety of healthy foods.

  • Exercise regularly.

  • Get enough sleep.

  • Drink lots of water.

Take Prenatal Vitamins

Pregnant women are encouraged to take prenatal vitamins, which are specifically prepared multivitamins, for both their personal health and the health of their unborn children.

Any nutritional inadequacies in your diet during pregnancy are made up for by these vitamins. While the supplements contain a variety of vitamins and minerals, the concentrations of folic acid, iron, and calcium are particularly significant.

Pregnancy prenatal vitamins are specially formulated multivitamins that mothers-to-be are advised to take for their own health as well as for the health of their babies.

These vitamins make up for any nutritional deficiencies in your diet during pregnancy.

Eat a Healthy Diet

While eating healthfully is important during your whole pregnancy, the first trimester is the most crucial for the growth and development of your unborn child.

Poor nutrition during pregnancy has the potential to modify a baby’s gene expression, which could then be passed on to subsequent generations.

Eating a balanced diet that is rich in fruits, vegetables, lean protein, and whole grains is important for both the mother and developing fetus.

Get Regular Exercise

Exercise during pregnancy can help promote a healthy pregnancy, reduce the risk of complications, and improve maternal health and well-being.

Regular exercise helps you combat the fatigue and mood and hormonal changes that happen in the first trimester. It also helps prevent weight gain and battle insomnia.

It’s recommended for you to engage in pregnancy exercises like walking, swimming, and prenatal yoga.

Get Plenty of Rest

Your body is going through tremendous changes and is developing an entirely new life-providing system for your baby.

You’ll probably experience extreme exhaustion on some days while the placenta develops. Additionally, you are experiencing significant hormonal and emotional changes.

Getting enough sleep and taking naps during the day can help alleviate fatigue and promote healthy fetal development.

Stay Hydrated

In order to make amniotic fluid, produce more blood, develop new tissue, deliver nutrients, improve digestion, and flush out waste and toxins, pregnant women require more water than non-pregnant people do.

Preterm labor can be prevented with hydration. Additionally, it guards against nausea, vertigo, and kidney stones. Staying hydrated can help you fight constipation and hemorrhoids if you’re already dealing with these problems.

What Not to Do

Make sure you pay attention to the following items:

  • Don’t smoke cigarettes or tobacco.

  • Don’t drink alcohol.

  • Don’t take illegal medication.

  • Don’t eat raw meat and do not overeat.

  • Don’t use hot tubs and sauna.

Quit Smoking

The CDC cautions against smoking during pregnancy. Smokers during pregnancy have a higher chance of miscarriage.

Smoking during pregnancy increases the risk of birth abnormalities, early birth, low birth weight, and infant mortality among unborn children.

Premature birth, low birth weight, birth abnormalities, and infant mortality are all more likely among babies born to mothers who smoked during pregnancy.

Don’t Drink Alcohol

Alcohol consumption is never safe during pregnancy. Even before a woman is aware that she is pregnant, alcohol usage during pregnancy might harm the unborn child.

Using alcohol during the first three months of pregnancy increases the risk of the baby being born with unusual facial features. It can increase the chance of miscarriage, early birth, and low birthweight in the unborn child. Even after your baby is born, it may still have an impact.

Drinking while pregnant increases the risk that your unborn child will acquire the severe, life-long illness known as foetal alcohol spectrum disorder (FASD).

If you drink alcohol during pregnancy you risk causing harm to your baby. Sometimes this can result in mental and physical problems in the baby, called foetal alcohol spectrum disorder (FASD).

Don’t Use Non-Prescription Drugs

A mother taking illegal drugs including cannabis, ecstasy, cocaine and heroin during pregnancy increases her risk for anemia, blood and heart infections, skin infections, hepatitis, and other infectious diseases.

Almost every drug passes from the mother’s bloodstream through the placenta to the fetus.

If you habitually use cocaine, heroin, or other opiates or opioids, don’t quit using them or cut back without first consulting a doctor. To lower the danger of issues for you and your unborn child, it’s crucial to stop using these drugs in the proper manner.

Don’t Eat Certain Types of Foods

According to studies, 50 percent of pregnant women gain too much weight. When that occurs, the newborn is more likely to become obese as an adult.

Doctors dispute on whether you need any extra calories during this first trimester, but you will require more calories throughout the second and third trimesters.

A pregnant person’s chance of developing listeriosis and toxoplasmosis increases if she consumes raw or undercooked meat or eggs. These can result in severe illnesses with a high mortality rate, birth abnormalities, and miscarriages.

Before eating, make sure your meat and eggs are well cooked.

Don’t Engage in Risky Activities

Avoid using the hot tub and sauna.

When you use a sauna, jacuzzi, hot tub, or steam room, it prevents your body from adequately expending heat through sweating and therefore raise your body temperature to 38 degrees Celsius or higher.

It’s likely that a considerable increase in body temperature during pregnancy, especially during the first 13 weeks, could be detrimental.

Instead, take a hot bath if you want to unwind.

What to Do in the Case of Pelvic Pain in the First Trimester?

Pelvic pain is a common symptom during pregnancy, particularly in the first trimester. While it is normal to experience some discomfort during this time, severe or persistent pelvic pain should be evaluated by a healthcare provider to ensure that there are no underlying complications.

Here are some things that a pregnant woman can do if she experiences pelvic pain during the first trimester:

Pelvic pain is very common pain during pregnancy that occurs in the lower part of your tummy.

Here are some things that a pregnant woman can do if she experiences pelvic pain during the first trimester:


It is important to rest as much as possible when experiencing pelvic pain. Avoid standing or sitting for long periods of time, and try to find a comfortable position that alleviates the pain.

Chiropractic Care

During pregnancy, the body undergoes significant changes that can cause misalignment in the spine and pelvis, leading to pelvic pain.

Chiropractic adjustments can help realign the spine and pelvis, reducing pressure on the nerves and muscles in the lower back and pelvic area, and alleviating pain.

Chiropractic care during pregnancy is safe and gentle. The pregnancy chiropractor will take extra care to ensure the comfort of the mother and the safety of the developing fetus during the treatment.

In addition to chiropractic adjustments, there are specific pregnancy exercises that may be recommended by chiropractors that help strengthen the pelvic muscles and alleviate pain.

Apply Heat or Cold

Applying heat or cold to the affected area can help alleviate pain and reduce inflammation. A warm bath or heating pad can help relax the muscles, while a cold pack can help reduce swelling.

Practice Pelvic Exercises

Pelvic exercises, such as Kegels, can help strengthen the pelvic muscles and reduce pain. It is important to speak with a healthcare provider to determine the appropriate exercises and frequency.

In the following video, Dr. Kimiya discusses some exercises you can do at home to strengthen your pelvic floor muscles.

Wear a Support Garment

Wearing a support garment, such as a maternity belt, can help alleviate pelvic pain by providing additional support to the lower back and abdomen.

Take Pain Relief Medication

Over-the-counter pain relief medication, such as acetaminophen, may be recommended by a healthcare provider to alleviate pelvic pain. However, it is important to avoid non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen during pregnancy.

Seek Medical Care

If pelvic pain is severe or persistent, it is important to seek medical care from a healthcare provider. They can evaluate the cause of the pain and provide appropriate treatment or referral if necessary.

The Takeaway

The first trimester of pregnancy is a critical time for fetal development and can be an exciting, yet challenging time for expectant mothers.

During this time, a woman’s body undergoes significant changes, including hormonal changes, fatigue, morning sickness, and breast tenderness.

It is important for pregnant women to prioritize their health during the first trimester by taking prenatal vitamins, eating a healthy diet, seeking chiropractic care using specific methods like the Webster Technique, getting regular exercise, and getting plenty of rest.

Additionally, it is important to avoid certain activities and substances that can harm the developing fetus, including smoking, alcohol, drugs, certain foods, and risky activities.

By following these guidelines and seeking medical care when necessary, pregnant women can help ensure a healthy pregnancy and fetal development during the first trimester.

Frequently Asked Questions

Pregnancy is typically divided into three trimesters, each lasting roughly 3 months, but the exact number of weeks in each trimester may vary slightly. Here’s the breakdown:

Trimester 1:

  • Weeks: 1 to 13 (inclusive)
  • Months: 1 to 3 (inclusive)

This trimester encompasses the initial development of the embryo and major organ systems.

Trimester 2:

  • Weeks: 14 to 27 (inclusive)
  • Months: 4 to 6 (inclusive)

This trimester is often considered the “golden period” with fewer physical discomforts for the mother and significant fetal growth.

Trimester 3:

  • Weeks: 28 to 40 (inclusive)
  • Months: 7 to 9 (inclusive)

This trimester focuses on fetal maturation and preparation for birth.

The first trimester of pregnancy lasts for about 12 weeks, or 3 months. This is the most crucial time for fetal development, as all the major organs and body systems begin to form.

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