Pregnancy lasts about 40 weeks and brings dramatic changes to both your body and your baby, starting well before you notice a bump. Some of what you’ll experience is uncomfortable, some is surprising, and most of it is completely normal. Here’s a trimester-by-trimester look at what’s actually happening and what you can do to stay on top of it.
First Trimester: Weeks 1 Through 12
The first trimester is when your body ramps up hormone production at a staggering pace. Your placenta starts producing a hormone called hCG almost immediately after conception, and its levels nearly double every three days for the first eight to ten weeks. hCG tells your body to stop menstruating and triggers a surge in progesterone and estrogen, which thicken your uterine lining and begin preparing your body to support a growing pregnancy. This hormonal flood is responsible for most of the classic early symptoms: nausea, breast tenderness, fatigue, and frequent urination.
Nausea (often called morning sickness, though it can strike at any hour) tends to peak around weeks 8 to 10, right when hCG levels are at their highest. For most people it eases off by weeks 12 to 14. Fatigue can feel extreme during these early weeks, partly because progesterone has a sedating effect and partly because your body is building an entirely new blood supply system from scratch.
Meanwhile, your baby is developing fast. Structures that will become the heart begin clustering around weeks five to six and can already pulse. By the end of the first trimester, all major organ systems have started forming, fingers and toes are taking shape, and the fetus is roughly the size of a lime.
Second Trimester: Weeks 13 Through 27
Many people call this the “easiest” trimester. Nausea usually fades, energy returns, and the pregnancy starts to feel more real as your belly grows. Your blood volume is climbing steadily during this stretch, eventually increasing by about 45% above your pre-pregnancy levels. That extra blood supports the placenta and your baby’s growth, but it also means your heart is working harder. Cardiac output rises by roughly 40%, driven mostly by a larger volume of blood pumped per heartbeat plus a heart rate that’s about 10 to 20 beats per minute faster than usual.
Blood pressure actually drops during the first and second trimesters because your blood vessels relax to accommodate all that extra volume. This can cause lightheadedness if you stand up too quickly, which is normal. Blood pressure climbs back to pre-pregnancy levels by the third trimester.
By the end of the fifth month, most people start to feel the baby move for the first time. Early movements feel like flutters or bubbles, and they become more distinct as the weeks go on. This is also the trimester when your belly becomes obviously visible, and you may notice round ligament pain (sharp twinges on one or both sides of your lower abdomen) as your uterus stretches.
Third Trimester: Weeks 28 Through 40
The final stretch brings the most physical discomfort. Your baby is gaining weight rapidly, putting pressure on your bladder, lungs, and lower back. Shortness of breath, heartburn, trouble sleeping, and swollen ankles are all common. The baby’s lungs are maturing during this period, producing a substance called surfactant that will help them breathe after birth.
You’ll likely start feeling Braxton Hicks contractions, sometimes called “practice contractions.” These are irregular tightening sensations in your uterus that do not follow a pattern and don’t get stronger over time. They’re usually felt in the front of the abdomen or in one specific area, and they tend to come and go unpredictably. They become more frequent as your due date approaches, which can make them confusing.
Braxton Hicks vs. Real Labor
True labor contractions are different in four key ways. They come at regular intervals and get closer together over time. They last 30 to 90 seconds and get longer. They grow stronger rather than fading away. And they typically start in your mid-back and wrap around to the front of your abdomen, rather than staying in one spot. If your contractions follow this pattern, it’s time to call your provider or head to your hospital or birth center.
How Much Weight You’ll Gain
Weight gain varies based on your pre-pregnancy size. The general guidelines break down like this:
- Underweight (BMI under 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 higher): 11 to 20 pounds
Most of this weight isn’t body fat. It includes the baby, the placenta, amniotic fluid, increased blood volume, breast tissue growth, and extra fluid your body retains. Weight gain tends to be slowest in the first trimester and fastest in the third.
Prenatal Visits and Screening Tests
The standard schedule for prenatal checkups follows a predictable pattern: once a month from weeks 4 through 28, twice a month from weeks 28 through 36, then weekly from week 36 until delivery. High-risk pregnancies require more frequent monitoring.
At your early visits, you’ll have blood work, urine tests, and an ultrasound to confirm how far along you are. Between weeks 24 and 28, you’ll do a glucose screening test, which involves drinking a sugary liquid and having your blood drawn to check for gestational diabetes. If you had gestational diabetes in a previous pregnancy or have other risk factors, this test may happen in the first trimester instead. Later in pregnancy, you’ll also be screened for Group B strep, a common bacterium that can be passed to the baby during delivery but is easily treated.
Nutrition, Supplements, and Caffeine
Folic acid is the single most important supplement in early pregnancy. You need 400 to 800 micrograms daily, ideally starting before conception, because it plays a critical role in preventing neural tube defects during the earliest weeks of development. Most prenatal vitamins contain this amount. Check the label to confirm, since formulas vary.
Caffeine doesn’t need to be eliminated entirely, but it should be limited. The American College of Obstetricians and Gynecologists recommends no more than 200 milligrams per day, which is roughly one 12-ounce cup of coffee. The reason for caution goes beyond the caffeine itself: your body processes caffeine much more slowly during pregnancy. By late pregnancy, caffeine’s half-life can stretch to 15 hours, meaning a single cup in the morning lingers in your system well into the night. This prolonged exposure affects both you and the baby.
Warning Signs That Need Immediate Attention
Most pregnancy symptoms are uncomfortable but harmless. A few, however, signal something potentially dangerous. The CDC identifies several urgent warning signs to watch for throughout pregnancy:
- A headache that won’t go away or gets worse, especially one that starts suddenly with severe pain, throbs on one side, or comes with blurred vision or dizziness.
- Vision changes such as seeing flashes of light, bright spots, blind spots, or sudden blurriness.
- Extreme swelling of your hands or face. This is not the mild ankle swelling common in late pregnancy. It’s swelling severe enough that you can’t bend your fingers, wear rings, or fully open your eyes.
- Vaginal bleeding heavier than spotting, fluid leaking from your vagina, or discharge with a foul odor.
These symptoms can indicate conditions like preeclampsia, placental problems, or infection. They don’t always mean something is wrong, but they require prompt evaluation because the conditions they point to can escalate quickly.
What Changes Feel Like Day to Day
Beyond the major milestones, pregnancy involves a long list of smaller shifts that no one warns you about. Your sense of smell may become almost comically heightened in the first trimester. Your gums might bleed more when you brush your teeth, thanks to increased blood flow. You may develop nasal congestion that lasts for months, sometimes called “pregnancy rhinitis,” caused by swollen blood vessels in your nasal passages.
Skin changes are common too. A dark line called the linea nigra may appear down the center of your belly. Some people develop darkened patches on their face. Stretch marks typically show up in the third trimester as the skin over your belly and breasts stretches rapidly. Mood swings, vivid dreams, and forgetfulness (“pregnancy brain”) are all reported frequently and are tied to the hormonal and sleep changes your body is managing.
Every pregnancy is different, and the intensity of these symptoms varies widely from person to person and even from one pregnancy to the next. What stays consistent is the general timeline: a hormonally intense first trimester, a more comfortable middle stretch, and a physically demanding final push before delivery.