The first trimester covers weeks 1 through 12 of pregnancy, and it’s the period when your baby’s major organs form, your body begins dramatic hormonal shifts, and you’ll need to establish prenatal care. Most of what you need to do falls into a few categories: getting to the doctor, adjusting your diet, managing symptoms, staying active, and knowing which warning signs need immediate attention.
Schedule Your First Prenatal Visit
As soon as you get a positive pregnancy test, call to book your first prenatal appointment. This visit is the longest one you’ll have. Your provider will go over your full medical history, measure your weight and height, calculate your BMI, and estimate your due date based on the first day of your last period. You’ll likely get a physical exam, including a pelvic exam and possibly a Pap test if you’re overdue for one.
Blood work at this visit checks your blood type and Rh factor, immunity to rubella and chickenpox, and exposure to infections like hepatitis B, syphilis, and HIV. You’ll also give a urine sample to screen for urinary tract infections. Your provider may offer an early ultrasound to confirm dating. After this first visit, expect appointments roughly every four weeks through the end of the trimester. By around 12 to 14 weeks, your provider can often pick up the baby’s heartbeat using a handheld Doppler device.
Genetic Screening Options
Between weeks 11 and 13, you’ll be offered optional screening tests that assess the chance of certain chromosomal conditions, primarily Down syndrome, trisomy 13, and trisomy 18. Combined first trimester screening involves a blood draw plus a specialized ultrasound that measures the fluid at the back of the baby’s neck (called nuchal translucency). Together, these give a risk estimate rather than a definitive diagnosis.
A newer option, noninvasive prenatal testing (NIPT), uses only a blood sample to analyze fragments of fetal DNA circulating in your bloodstream. It can screen for the same conditions as the combined test, plus some additional chromosomal differences. A first trimester ultrasound is still recommended alongside NIPT. These are screening tests, not diagnostic ones, so if results come back elevated, your provider will discuss follow-up options.
What’s Happening With Your Baby
Development moves fast in the first 12 weeks. By week 5, the neural tube that becomes the brain and spinal cord is forming, and a tiny heart tube is already pulsing around 110 times per minute. By week 6, the structures that will become the ears, eyes, and mouth start taking shape. Week 7 brings the beginnings of bone formation and early genital development.
By week 8, all the major organs and body systems are developing. Teeth and taste buds start forming around week 9. Fingernails, toenails, and external ears appear by week 10. At week 12, all the organs, limbs, bones, and muscles are present. The circulatory, digestive, and urinary systems are functional, and the liver is producing bile. Everything from here forward is growth and refinement.
Start Folic Acid Right Away
If you aren’t already taking folic acid, start immediately. The CDC recommends 400 micrograms daily to help prevent neural tube defects, which are serious birth defects of the brain and spinal cord. Ideally, you’d be taking it before conception, since the neural tube forms so early (around week 5) that many people don’t even know they’re pregnant yet. Most prenatal vitamins contain at least this amount.
Foods and Substances to Avoid
Pregnancy suppresses parts of your immune system, making you more vulnerable to foodborne illness. The CDC identifies several categories of higher-risk foods to avoid or handle carefully:
- Raw or undercooked meat and poultry, including unheated deli meat, cold cuts, hot dogs, and dry sausages
- Raw or undercooked eggs, including foods made with them like homemade Caesar dressing, raw cookie dough, and homemade eggnog
- Raw or undercooked seafood, such as sushi, sashimi, and ceviche, plus refrigerated smoked fish (labeled “lox,” “nova-style,” or “kippered”)
- High-mercury fish, specifically shark, swordfish, king mackerel, and tilefish
- Unpasteurized dairy and juice, including raw milk and soft cheeses like queso fresco, brie, camembert, and blue-veined cheese
- Premade deli salads like potato salad, chicken salad, and coleslaw from a deli counter
- Raw sprouts of any kind, and unwashed fresh fruits and vegetables
- Raw flour, including raw dough or batter
Alcohol has no known safe amount during pregnancy. Caffeine in moderate amounts (generally under 200 mg per day, or about one 12-ounce cup of coffee) is widely considered acceptable, but your provider can give personalized guidance.
Managing Nausea and Other Symptoms
Nausea affects the majority of pregnant people in the first trimester and typically peaks between weeks 8 and 10. Despite its name, “morning sickness” can hit at any time of day. Eating small, frequent meals, keeping crackers by the bed, and avoiding strong smells all help. Ginger is one of the better-studied natural remedies: clinical trials have used 250 mg of ginger four times a day and found it effective at reducing nausea. Vitamin B6 at 40 mg twice daily has also shown comparable benefits.
Fatigue is nearly universal in the first trimester because your body is diverting enormous energy toward building a placenta and supporting rapid fetal growth. Rest when you can, and don’t feel guilty about going to bed earlier than usual. Breast tenderness, frequent urination, and food aversions are also common and generally ease as you move into the second trimester.
Exercise During the First Trimester
Physical activity is safe and recommended for uncomplicated pregnancies. The goal is at least 150 minutes of moderate-intensity aerobic activity per week, spread across multiple days. Walking, swimming, stationary cycling, and prenatal yoga all qualify. If you were already running, lifting, or doing other vigorous exercise before pregnancy, you can generally continue.
Research has not substantiated concerns that regular exercise causes miscarriage, poor fetal growth, or premature delivery in healthy pregnancies. The main activities to avoid are contact sports with a risk of abdominal impact and anything with a high fall risk, like downhill skiing or horseback riding. Lying flat on your back during exercise becomes a concern after 20 weeks, not during the first trimester.
Medication Safety
For headaches or minor aches, acetaminophen (Tylenol) is considered safe throughout pregnancy. Ibuprofen and naproxen (Advil, Aleve) are generally not recommended, especially during the first trimester when organ formation is underway. For allergies, antihistamines like loratadine (Claritin) and cetirizine (Zyrtec) are acceptable options. If you develop a cough, dextromethorphan (the active ingredient in many cough suppressants) appears to be safe. Oral decongestants, particularly phenylephrine, should be avoided in the first trimester.
Environmental Precautions
Cat litter is the most commonly cited household risk because of a parasite called toxoplasma, which can cause serious birth defects. The parasite spreads through the feces of infected cats, as well as through contaminated soil and water. If you have a cat, have someone else handle litter box duty. If that’s not possible, wear disposable gloves and wash your hands thoroughly afterward. Change the litter daily, since the parasite becomes infectious after sitting for more than 24 hours. The same precaution applies to gardening: wear gloves, since outdoor cats may have used your garden beds.
Weight Gain Expectations
Most people gain 2 to 4 pounds during the entire first trimester. That’s it. Some gain nothing, and some lose a few pounds due to nausea. The bigger weight changes come later, when the typical pattern is about a pound per week through the second and third trimesters. Total pregnancy weight gain depends on your starting BMI: 25 to 35 pounds for those at a normal weight, 15 to 25 pounds for those who are overweight, and 28 to 40 pounds for those who are underweight.
Warning Signs That Need Immediate Attention
Some first trimester symptoms are always worth a call. Vaginal bleeding that goes beyond light spotting (anything resembling a period), fluid leaking from the vagina, or discharge with a foul smell should be evaluated promptly. Severe belly pain that is sharp, stabbing, or cramp-like and doesn’t go away, or pain that starts suddenly and worsens over time, needs immediate medical attention. A fever of 100.4°F or higher also warrants a call to your provider, as it can signal an infection that may need treatment.