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A Guide to the First Trimester of Pregnancy

A Guide to the First Trimester of Pregnancy

Congratulations and welcome to the wondrous world of pregnancy. Your first trimester can sometimes feel like a whirlwind of physical and emotional changes, but much of that is your body adjusting and adapting to its new role as the home of your growing baby.

How long is the first trimester?

The first trimester starts from week one and goes through week 12. Week one is considered the date of your last menstrual period. You’ll be finished with the first trimester at the end of week 12, or after about three months.

Baby growth during the first trimester

Your baby is having a busy three months!

Pregnancy weeks 1-4

  • After conception, the fertilized egg, known as a zygote, will be dividing into multiplying cells and traveling down the fallopian tube. They'll eventually navigate to the uterus, where they'll implant and make your baby’s home for the next nine months.
  • The neural tube, which later becomes the baby's brain and spinal cord, starts developing.
  • Your baby reaches embryo status by week four, and the beginning of a placenta, a pancake-shaped organ that connects to your baby through the umbilical cord, will start to form.

Pregnancy weeks 5-8

  • At the beginning of week five, your baby may look kind of like a tadpole, but their nose, mouth, hands, and buds that will turn into arms and legs are starting to form.
  • What color eyes or hair will your baby have? The chromosomes are already in place to determine those characteristics.
  • That little heart will start beating!
  • The neural tube, the precursor to the brain, spinal cord, and central nervous system, continues to form.
  • The placenta, as well as the amniotic sac where your baby will grow, are still developing.

Pregnancy weeks 9-12

  • Your baby will grow from the size of a cherry to a lime and transition from an embryo to a fetus.
  • Limb buds are starting to turn into visible arms and legs, along with teensy feet and hands.
  • Eyes, eyelids, and ears are becoming more distinct.
  • By week 12, almost all of your baby’s internal organs are formed, including the kidney and digestive system.
  • Vocal cords that will be saying “mama” before you know it, are developing, too.
  • The placenta,which will become your baby’s lifeline to everything they need to eat, breathe, and develop, fully forms.

First trimester body changes

While your baby’s moving, grooving, and growing on the inside, your body may not have changed much visibly on the outside yet. In fact, you may have just missed your period and not even know you’ve got a teeny tiny bun in the oven. But rest assured, there are lots of things going on, and you’ll feel it soon enough!

First trimester pregnancy indicators and body changes

  • Your baby’s increasing demands may drain your energy and leave you feeling exhausted.
  • One of the most notorious first-trimester pregnancy indicators is morning sickness. Ginger, vitamin B6, and even acupressure bracelets may provide some relief.
  • Your breasts and nipples may feel tender and sore.
  • You may notice that you have a heightened sense of smell, which may turn you off to some foods—even some of your usual favorites.
  • There may be light red or brown spotting.
  • You may need to urinate more.
  • You may have white cervical mucus due to changes in the mucus lining in your cervix.
  • Hormonal changes may contribute to mood swings, headaches, and a rosy pregnancy “glow.”
  • Pregnancy hormones that relax the digestive tract may contribute to burping and gas.
  • While you might not have a baby bump by 12 weeks, especially if you’re a first-time mom, you might feel a little bloated and bigger.

First trimester pregnancy checklist

You’re at the beginning of a magnificent journey. Being prepared can help alleviate stress while your body adapts to your special arrival. Here are some first trimester to-dos:

Schedule your first prenatal visit with your doctor. You’ll get an exam, have some blood work done, discuss your health history, lifestyle, and medications, and talk about steps you can take to avoid certain birth defects and pregnancy complications. You’ll also find out that all-important due date! This is performed by ultrasound in most cases.

Take a prenatal supplements (as advised by your doctor). Navigating nutrition can be a lot easier with the help of prenatal supplements, which are packed with essential vitamins and nutrients for baby’s healthy development.

When considering prenatal vitamins, look for ones that have folic acid and DHA (docosahexaenoic acid). Folic acid is vitamin B9, and research has shown that taking 400 milligrams of folic acid (found in most leading prenatal vitamins) daily throughout your pregnancy can help reduce the risk of major birth defects to your baby's brain and spine.1

DHA is an omega-3 fatty acid that helps encourage healthy brain development. The American Pregnancy Association recommends that pregnant women take a daily supplement with a minimum of 300 milligrams of DHA.2

Avoid smoking and alcohol. Your baby’s health is very important, and avoiding tobacco and alcohol while pregnant can help protect them from serious harm. While pregnancy can be stressful at times, it’s best to avoid these substances and any recreational drug use to promote your and your baby’s health.

Numerous pregnancy complications and health problems, including low birth weight, birth defects, and preterm delivery, have been linked to smoking.3

Experts say there’s no safe amount of alcohol use during pregnancy. Drinking alcohol puts your baby at a disadvantage for birth defects and other serious health issues.4

Consider genetic screenings. Your doctor will most likely conduct some routine prenatal tests to monitor your baby’s development and check for potential health problems. You may also be offered some optional tests, such as screenings that can provide insights into the probability for certain genetic conditions.

Support your energy. Making sleep a priority, napping whenever you feel tired, and moderate exercise can all empower you with more energy.

Watch what you eat. A well-balanced diet filled with nutrient-rich foods can help both you and your baby. You’ll also want to avoid some foods, such as raw fish or eggs (like in cookie dough) that could introduce possible contaminants.

Limit your coffee intake. Coffee and tea have caffeine, which is a stimulant that can raise your blood pressure. It crosses into the placenta and may affect your baby. Try to limit your intake to about one cup per day.5

Drink more water. When you're pregnant, you need more water to support your higher blood volume, your baby’s circulation, and amniotic fluid. Water also helps flush out toxins and waste and aids digestion. Aim for a water intake of at least 8-10 glasses a day.

Try some morning sickness relief strategies. While it may be obvious, avoid nausea-triggering foods and smells whenever possible. Eating dry crackers first thing in the morning may also help. And be sure to keep drinking those fluids (always a good idea!) since vomiting can cause dehydration. If you have severe morning sickness, see your doctor.

Get ready to share the news. One of the most fun things about pregnancy can be thinking of creative ways to announce the news! While close family and friends may already know, the beginning of the second trimester is when many expecting parents decide to “go public.”

Join Enfamil Family Beginnings

If you thought the first trimester of pregnancy was exciting, wait until you see what’s in store for the second and third trimesters. Start preparing for all the amazing changes pregnancy and parenthood will bring with Enfamil Family Beginnings. It’s the perfect resource for new and expecting moms. Save on Enfamil products, track your bump and baby’s growth, and get helpful articles each week relevant to your journey. Join now for up to $400 in free gifts.








All information on, including but not limited to information about health, medical conditions, and nutrition, is intended for your general knowledge. It is not a substitute for a healthcare professional's medical identification, advice, or management for specific medical conditions. You should seek medical care and consult your doctor, OB-GYN, or pediatrician for any specific health or nutrition issues. Never disregard professional medical advice or delay seeking medical care because of something you have read on


All information on Enfamil, including but not limited to information about health, medical conditions, and nutrition, is intended for your general knowledge and is not a substitute for a healthcare professional's medical identification, advice, or management for specific medical conditions. You should seek medical care and consult your doctor or pediatrician for any specific health or nutrition issues. Never disregard professional medical advice or delay seeking medical treatment, care, or help because of information you have read on Enfamil.