Skip to main content

First Trimester of Pregnancy: An Experts’ Guide

An essential guide (containing advice from Dr. Peter J. D’Adamo) to common first trimester symptoms & health conditions, prenatal supplements and exercise.
What to Expect in the First Trimester of Pregnancy
Updated: December 2, 2021

The first trimester is the most critical time in your pregnancy. Although the fetus at the end of the first trimester is only about 4 inches long and weighs less than 1 ounce, your baby’s development is in full swing. Their major organs and nervous system, heartbeat, arms, fingers, legs, toes, hair, and buds for future teeth have begun to form, making it vital for mom to start right off the bat with a healthy pregnancy.

This is not a time to skimp on food or count calories. You're not entirely eating for two people, but you do need extra nutrients for your growing fetus, especially in the second and third trimesters.

If you are a healthy weight pre-pregnancy, you'll need to gain 25 to 35 pounds during your pregnancy. Overweight women should gain slightly less, while underweight women will need to gain a bit more. During early pregnancy, there is no need to tack on additional calories; however, during the second trimester, you’ll need about 340 more calories per day, and in the third, approximately 450. This will allow you to nourish your fetus and store nutrients for breastfeeding.

Look for whole grains, lean protein, low-fat dairy, and fresh fruits and vegetables when choosing foods.

Common First Trimester Conditions

First Trimester Conditions

Some women experience a whole slew of pregnancy symptoms during the first trimester, while others may not even realize they’re pregnant until they’ve missed a period. While each pregnancy is different, there are some common symptoms of pregnancy that many women will experience during the early weeks of pregnancy.

Implantation Bleeding and Cramping

Some women experience a cramping-like sensation and a small amount of spotting when the fertilized egg implants itself into the uterus. Because it is often so mild many women mistake this as the beginning of their menstrual cycle.

If, however, you notice cramping and spotting and your period does not arrive, you may wish to take a home pregnancy test. If you discover you are pregnant, contact your obstetrics office or a local women’s health clinic to begin your prenatal care.

Tender Breasts

Although your body won’t produce milk for quite some time, one of the earliest signs of pregnancy for many women is enlarged and tender breasts. You may also notice that your areolas or nipples grow darker in color.

Morning Sickness and Nausea

Nausea and digestive system problems called morning sickness are common symptoms many women experience during the first trimester of pregnancy resulting from hormonal changes.

Morning sickness (which can happen any time of the day) may be a good sign, though you may not feel particularly grateful. Some scientists believe that morning sickness evolved as a natural way of protecting women against foods that might contain dangerous microorganisms or parasites or foods whose chemical compositions might prove harmful to fetal development.

Another reason for morning sickness is increased levels of the hormone beta-hCG. However, since high levels of beta-hCG tend to protect against miscarriage, look on the bright side: your morning sickness may well be an early sign that your pregnancy is off to a good start. Morning sickness usually disappears after the first trimester.

Mood Swings

Women are often surprised that they don't feel buoyant at the start of pregnancy, especially when it is a long-awaited result. The stresses of the first trimester can produce many emotional ups and downs. So although you may be delighted that you're pregnant, the hormonal adjustments you're experiencing can make you feel anything but joyous.

An increase in your progesterone levels can cause mood swings, fatigue, and insomnia. Your entire system is fully engaged in creating a healthy environment for your fetus by producing the placenta. This process completes at the end of month three, and many women feel a return of their energy in the fourth month.

You may also be feeling anxious about becoming a parent, ensuring you have a healthy pregnancy, and wondering what all the stages of pregnancy will bring you.

Constipation, Indigestion, and Heartburn

Constipation is a fact of life for most pregnant women. Hormonal changes are primarily responsible, signaling food to move more slowly through your system as it nourishes your fetus.

Your body’s slowed digestive tract may also lead to indigestion and heartburn. If you notice frequent heartburn, keep a food journal to see if you can track down the culprit(s).

Try eating smaller meals and drinking plenty of water to help. Also, avoid laying down for at least 30-minutes after a meal.

Food Aversions and Cravings

The food cravings and aversions that many women experience during pregnancy are something of a mystery. While you may crave what's good for you and be repelled by harmful foods, it doesn't always work that way. Your best strategy is to eat what's right for you and try to find replacements within your diet for the harmful foods you may crave.

What Supplements and Medications Should I Take or Avoid?

First Trimester Medications

The American College of Obstetricians and Gynecologists recommends that all women attempting to become pregnant take a prenatal vitamin daily. Because a woman can be pregnant for several weeks before realizing it, it is essential anyone actively trying to become pregnant take folic acid and prenatal vitamins to help prevent neural tube defects and other potential abnormalities.

Pregnant women and breastfeeding women also need to be careful about which over-the-counter and prescription medications they take, as these can cause congenital disabilities or pass through breast milk in some instances. If you are thinking about becoming pregnant or actively trying to become pregnant, speak with your health care provider about your current medications.

Prenatal Supplements

Speak with your OB-GYN first, but any of the commercial prenatal multivitamins should be adequate. However, many are made with synthetic components rather than the preferred whole food ingredients. Choose a blend of the B vitamins, along with antioxidants. Look for quality, not quantity. Not all formulations release the specified amount of nutrients on the label.

Your daily prenatal vitamin/mineral supplement probably doesn't give you enough calcium. Most daily prenatal formulas only contain about 200 to 300 milligrams of calcium, about 1,000 milligrams less than you and your baby need every day. You'll want to ensure that you get at least 1,200 milligrams of calcium every day from natural food sources and supplements.

Despite the benefits of prenatal vitamins for a pregnant woman’s health, the Mayo Clinic advises against simply taking a prenatal vitamin as a daily vitamin unless you are pregnant or actively trying to become pregnant. In addition, they advise that a person with a well-rounded diet typically does not need any additional supplements when not pregnant.

DHA Supplementation

A natural nutrient for humans of all ages, DHA, an omega-3 long-chain polyunsaturated fatty acid, is one of the essential building blocks of human brain tissue. Found naturally in breast milk, DHA is also present in egg yolk and oily fish, like salmon and sardines.

DHA is important for signal transmission in the brain, eye, and nervous system, whether you’re a baby or an adult. Your developing baby receives the DHA through the blood via the placenta and umbilical cord.

Seventy percent of the brain cells are formed before birth. These cells are mainly composed of essential fatty acids, with DHA being the most important because it gives great flexibility to the cell membranes. Flexibility is essential for fast and accurate message transfer in the brain.

During pregnancy, the recommended intake of DHA is 300 milligrams per day in food and supplements. Studies have shown that diets deficient in DHA are often linked with low head circumference, low placental weight, and low birth weight in their babies.


Taking any medication while pregnant can carry a risk; however, the FDA has created a categorization system to break down medication risk factors for all three trimesters and nursing.

Your doctor will consult this list to answer any questions you may have about over-the-counter or prescription medications you may be taking or wish to take to relieve common cold or allergy symptoms. In addition, the CDC has advised that all pregnant women receive a flu shot and their COVID-19 vaccination and booster shot if eligible.

Exercise in the First Trimester

Physical activity during pregnancy is healthy and recommended. Even a simple task like walking twenty to thirty minutes a day is beneficial to you and your baby. Regular exercise can help you maintain healthy blood pressure, healthy weight gain and reduce symptoms of fatigue and anxiety.

Pregnancy can be stressful. Your feelings, fears and expectations about yourself, your family, and the impending arrival of your baby are important, too. To make matters a bit more complicated, your emotions can be affected by the dramatic hormonal changes you're experiencing. One of the essential functions of exercise is reducing stress and improving your mental condition.

Exercise Guidelines

Exercising three to four times a week is recommended for pregnant women during the first trimester. In most cases, women can continue to exercise until their due date. Always pay attention to the signals your body is sending you on when to rest and stay hydrated.

Exercise is good for your baby, too. Studies show that babies born to moms who exercise during pregnancy may benefit from better stress tolerance and advanced neurobehavioral maturity. These children are leaner at five years of age and have better early neurodevelopment.

The new findings are added to the already-known benefits of exercise during pregnancy, including improved cardiovascular function, improved attitude and mood, easier and less complicated labor, quicker recovery, and improved fitness.

Additional Tips for Exercising While Pregnant

  • All aerobic exercise is not of equal value. If your regular workout involves contact sports or in-line skating, you should forgo them during pregnancy to avoid any potential injury to the abdominal area.
  • Make your aerobic exercises the low-impact variety. For example, if you take dance or movement classes, keep your feet on the floor—no jumping or bouncing. Or choose exercises such as cycling, swimming, or brisk walking that have little or no impact risks.
  • Take extra time to warm up and properly stretch your muscles before exercising.
  • Wear a good support bra to protect your breasts and limit discomfort, especially if they feel tender.
  • Drink plenty of water throughout the workout.
  • Don't exercise on an empty stomach. Eat a snack 30 minutes before exercising.

Though exercise in pregnancy is generally safe, moms-to-be embarking on an exercise program should be aware of warning signs. If any of these symptoms occur, stop exercising and contact your practitioner.

  • Sudden and severe abdominal pain
  • Uterine contractions lasting 30 minutes once exercising stops
  • Dizziness; and vaginal bleeding.
  • Decreased fetal activity
  • Visual disturbances
  • Numbness in any part of the body.

For some women, such as those with heart disease, blood clots, recent pulmonary embolism, or those who have a "high-risk" pregnancy, exercise may not be recommended. In taking the complete medical history, your practitioner will determine if maternal conditions limit or exclude an exercise program.

For more information on how to stay healthy during the first trimester, check out Eat Right for Your Baby: The Individualized Guide to Fertility and Maximum Health During Pregnancy by Dr. Peter J. D'Adamo and Catherine Whitney.


L. Elizabeth Forry

About L. Elizabeth Forry

L. Elizabeth Forry is an Early Childhood Educator with 15 years of classroom… Read more

Join the Family

Your partner in parenting from baby name inspiration to college planning.