Pregnancy lasts about 40 weeks from the first day of your last menstrual period and is divided into three trimesters, each bringing distinct changes for both you and the developing baby. Whether you just found out you’re pregnant or you’re still planning, here’s a practical guide to what happens, what to expect at your appointments, and how to take care of yourself along the way.
Early Signs of Pregnancy
A missed period is the most recognized sign, but many symptoms show up before that. Breast tenderness and fatigue can appear as early as one to two weeks after conception, driven by a surge in progesterone. Nausea, often called morning sickness despite striking at any hour, typically begins between two and eight weeks after conception and can last well into the second trimester or beyond.
About 25% of pregnant women experience light spotting around six to 12 days after conception, when the fertilized egg implants in the uterine wall. This bleeding is lighter in color than a normal period and is common throughout the first 12 weeks. Other early symptoms include headaches, food cravings or aversions, mood swings, and frequent urination. That last one is caused by a hormone called hCG, which increases blood flow to the pelvic area in the first few weeks.
How Your Baby Develops by Trimester
First Trimester (Weeks 1 Through 12)
During the first eight weeks, the fertilized egg goes from a tiny cluster of cells to an embryo with a recognizable head, eyes, mouth, and limb buds. Cells that form the heart begin clustering around weeks five to six and start pulsing. By the end of week eight, most organs and body systems have taken shape. At week nine the embryo is officially called a fetus, and biological sex is determined, though it’s too early to see on ultrasound.
Second Trimester (Weeks 13 Through 26)
This is when many people start to feel better as nausea fades. The baby grows rapidly, developing facial features, fingerprints, and the ability to move. You’ll likely feel those first flutters of movement, called quickening, somewhere between weeks 16 and 22. By the anatomy scan around week 20, the baby’s organs are developed enough to examine in detail on ultrasound, and you can find out the sex if you want to.
Third Trimester (Weeks 27 Through 40)
The baby gains most of its weight in these final months, and the lungs and brain undergo critical maturation. You may notice more frequent kicks, hiccups, and shifts in position. Common discomforts include back pain, heartburn, swelling in the feet and ankles, and difficulty sleeping as your belly grows. The baby typically moves into a head-down position by week 36 in preparation for delivery.
Prenatal Visit Schedule and Key Tests
For an uncomplicated pregnancy, visits generally follow this pattern: every four weeks until 28 weeks, every two weeks until 36 weeks, then weekly until delivery. Each visit typically includes a blood pressure check, a urine test, and measurement of your belly to track growth.
Several screenings are scheduled at specific windows:
- Weeks 11 to 13: A nuchal translucency ultrasound measures a space at the back of the baby’s neck to screen for chromosomal conditions like Down syndrome. A first-trimester blood screening is done at the same time.
- Weeks 13 to 16: A blood test screens for chromosomal abnormalities and neural tube defects.
- Weeks 18 to 20: The anatomy scan, a detailed ultrasound that examines the baby’s organs, limbs, and overall development.
- Weeks 24 to 28: A glucose tolerance test screens for gestational diabetes. You’ll drink a sugary solution and have blood drawn about an hour later.
Nutrition and Prenatal Vitamins
A few nutrients need special attention during pregnancy. Folic acid is the most time-sensitive: all women who could become pregnant should get 400 to 800 micrograms daily from supplements or fortified foods. Folic acid is critical for preventing neural tube defects, and the neural tube forms very early, often before you know you’re pregnant. Once pregnant, the recommended intake rises to 600 micrograms per day.
Iron needs nearly double during pregnancy, to 27 milligrams per day, because your blood volume increases significantly to support the baby. Low iron is one of the most common nutritional deficiencies in pregnancy and can leave you feeling exhausted beyond the normal fatigue. Iodine requirements go up to 220 micrograms daily to support thyroid function and brain development. Calcium stays at 1,000 milligrams per day for adults (1,300 for teens), but if you’re not getting enough from food, the baby will draw calcium from your bones.
A standard prenatal vitamin covers most of these bases, but check the label to make sure it includes iron and iodine, since not all formulas do.
Foods to Avoid
Pregnancy suppresses parts of your immune system, making you more susceptible to certain foodborne infections. Listeria is the biggest concern because it can cross the placenta and cause serious complications even when your own symptoms are mild.
Foods to skip or handle carefully:
- Deli meats and hot dogs unless heated until steaming
- Soft cheeses made from unpasteurized milk, including queso fresco, brie, camembert, and blue cheese
- Raw or undercooked eggs, including homemade Caesar dressing, cookie dough, and eggnog
- Raw or undercooked meat, poultry, and seafood, including sushi and ceviche
- Unpasteurized milk and juice
- Raw sprouts like alfalfa and bean sprouts
- Refrigerated smoked seafood (labeled “lox,” “nova-style,” or “kippered”) unless cooked into a dish
For mercury, avoid shark, swordfish, king mackerel, and tilefish entirely. These large, long-lived fish accumulate mercury levels high enough to affect fetal brain development. Lower-mercury options like salmon, shrimp, and tilapia are safe and provide beneficial omega-3 fatty acids.
Weight Gain Guidelines
How much weight you should gain depends on your pre-pregnancy BMI. The current guidelines, based on recommendations from the Institute of Medicine, break down as follows for a single baby:
- Underweight (BMI below 18.5): 28 to 40 pounds
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds
- Overweight (BMI 25 to 29.9): 15 to 25 pounds
- Obese (BMI 30 or above): 11 to 20 pounds
For twins, the ranges are higher: 37 to 54 pounds for normal-weight women, 31 to 50 for overweight women, and 25 to 42 for obese women. Most of the weight gain happens in the second and third trimesters. Gaining too little increases the risk of a small baby, while gaining too much raises the likelihood of gestational diabetes and delivery complications.
Exercise During Pregnancy
The current recommendation is at least 150 minutes of moderate-intensity aerobic activity per week, spread across several days rather than crammed into one or two sessions. Walking, stationary cycling, swimming, water aerobics, dancing, and resistance training with weights or bands have all been studied extensively in pregnancy and found to be both safe and beneficial.
If you were active before pregnancy, you can generally continue your routine, including vigorous exercise, with a few modifications. After 20 weeks, avoid exercises that have you lying flat on your back for extended periods, because the weight of the uterus can compress major blood vessels and lower your blood pressure. Stay hydrated, wear loose clothing, and avoid exercising in high heat or humidity, especially in the first trimester when overheating poses the greatest risk.
Mental Health During Pregnancy
Perinatal mood disorders, including depression and anxiety, are far more common than many people realize. They can begin during pregnancy, not just after delivery, and look different from the stereotypical image of postpartum depression. Persistent sadness, loss of interest in things you usually enjoy, racing thoughts, irritability that feels out of proportion, difficulty bonding with the pregnancy, and changes in sleep or appetite that go beyond normal pregnancy discomfort are all worth mentioning to your provider.
Screening for depression, anxiety, and PTSD is now a standard part of prenatal care. About one in five women who screen positive for depression may actually have bipolar disorder, which requires a different treatment approach. If you’ve ever experienced episodes of unusually elevated mood or energy, let your provider know, as this history changes how treatment should be managed.
Warning Signs That Need Immediate Attention
Most pregnancy discomforts are harmless, but certain symptoms signal potentially life-threatening conditions like preeclampsia, placental problems, or infection. Get medical care right away if you experience any of the following:
- A severe headache that doesn’t respond to rest or fluids, especially if it comes on suddenly or is accompanied by blurred vision or dizziness
- Vision changes such as seeing flashing lights, bright spots, blind spots, or sudden blurriness
- Extreme swelling of the hands or face, particularly if your fingers feel stiff, your rings won’t fit, or your eyes look puffy. This is different from the mild ankle swelling common in late pregnancy.
- Vaginal bleeding heavier than light spotting, or fluid leaking from the vagina
- A noticeable decrease in fetal movement. There’s no magic number of kicks to count. What matters is a change from your baby’s normal pattern.
Trust your instincts. If something feels off even when it doesn’t match a specific item on this list, it’s worth a call to your provider. Pregnancy complications are most treatable when caught early.