Pregnancy lasts about 40 weeks from the first day of your last period, and your body changes dramatically across all three trimesters. Some of those changes are uncomfortable, some are exciting, and most are completely normal. Here’s a practical walkthrough of what happens to your body, your baby, and your medical care from the positive test to delivery day.
First Trimester: Weeks 1 Through 12
The first trimester is when pregnancy hormones hit your system hard. A hormone called hCG, produced almost exclusively by the placenta, rises sharply in these early weeks and is a major driver of nausea and vomiting. Progesterone thickens the uterine lining to support the embryo, while estrogen helps maintain the pregnancy overall. The combined effect of these hormones touches nearly every organ system, which is why the symptom list feels so long: extreme tiredness, tender and swollen breasts, frequent urination, constipation, headaches, heartburn, food cravings or aversions, and mood swings.
Morning sickness is a misleading name because it can strike at any hour. For most people it peaks between weeks 8 and 12 and then gradually fades. Weight can go either direction in the first trimester, especially if nausea makes eating difficult.
Meanwhile, your baby’s development is moving fast. By the end of week five, a tiny tube that will become the heart is already pulsing about 110 times per minute. By week six, a provider can sometimes detect those pulses on a vaginal ultrasound. By week nine, the heartbeat is typically audible with a handheld Doppler device. Major organs and body structures begin forming during this period, which is why the first trimester is considered the most sensitive window for development.
Second Trimester: Weeks 13 Through 28
Most people find the second trimester noticeably easier. Nausea and fatigue tend to fade, energy returns, and you start to feel more like yourself. This is also when pregnancy becomes visible to the outside world as your belly grows.
The big milestone of this trimester is quickening, the first time you feel the baby move. For most people, this happens around the end of the fifth month. Early movements feel like a flutter or bubbles, and they become stronger and more recognizable over the following weeks. By month four, a provider can hear the fetal heartbeat loud and clear on a Doppler.
Your anatomy scan, a detailed ultrasound that checks the baby’s organs and body systems, typically happens between weeks 18 and 20. This scan confirms proper growth, checks for structural concerns, and can reveal the baby’s sex if you want to know. Around weeks 26 to 28, you’ll also have a glucose tolerance test to screen for gestational diabetes. This involves fasting, drinking a sugary solution, and having your blood drawn over several hours to see how your body processes sugar.
Inside the womb, the baby’s lungs begin developing around week 15, though they won’t be functional outside the body for months. By week 24 the lungs are formed but still too immature to work on their own. At week 26, the lungs start producing surfactant, a substance the baby will need to breathe air after birth.
Third Trimester: Weeks 29 Through 40
The final stretch brings a new set of physical challenges as the baby grows rapidly and takes up more space. Shortness of breath, back pain, heartburn, trouble sleeping, and frequent urination all tend to intensify. Swelling in the feet and ankles is common. Braxton Hicks contractions, irregular tightening sensations in the uterus, may start and are generally harmless practice contractions.
By month eight, most organs other than the lungs and brain are well formed and ready for birth. The lungs are close to fully developed by month nine. During these final weeks, the baby typically settles into a head-down position in preparation for delivery.
Your prenatal visits increase in frequency during this trimester: twice a month from weeks 28 through 36, then weekly from week 36 until birth. Providers use these visits to monitor your blood pressure, check the baby’s position, and track growth.
How Much Weight Gain Is Normal
Recommended weight gain depends on your pre-pregnancy body mass index. For a single pregnancy, the general targets are:
- Underweight (BMI under 18.5): 28 to 40 pounds
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds
- Overweight (BMI 25.0 to 29.9): 15 to 25 pounds
- Obese (BMI 30.0 to 39.9): 11 to 20 pounds
If you’re carrying twins, the numbers are significantly higher. A person with a normal pre-pregnancy BMI carrying twins would aim for 37 to 54 pounds. Most weight gain happens in the second and third trimesters, and it reflects not just fat stores but also the baby, placenta, amniotic fluid, increased blood volume, and breast tissue.
Prenatal Vitamins and Nutrition
Folic acid and iron are the two most critical supplements during pregnancy. The World Health Organization recommends 400 micrograms of folic acid daily along with 30 to 60 milligrams of iron. Folic acid is essential in early pregnancy because it helps prevent neural tube defects in the baby’s brain and spine. Iron supports the dramatic increase in blood volume your body needs to supply oxygen to the placenta. Most prenatal vitamins cover both, but it’s worth checking the label to confirm the amounts.
Starting a prenatal vitamin before conception or as early as possible gives the best protection, since the neural tube forms in the first few weeks, often before you even know you’re pregnant.
Foods and Substances to Avoid
Several foods carry specific risks during pregnancy. High-mercury fish, including swordfish, shark, king mackerel, and bigeye tuna, can damage the baby’s developing nervous system. Raw or undercooked seafood, meat, poultry, and eggs raise the risk of foodborne illness, which hits harder during pregnancy because your immune system is partially suppressed.
Hot dogs and deli meats can harbor listeria, a bacteria that causes a rare but serious infection particularly dangerous to pregnant people. Unpasteurized milk, soft cheeses like brie and feta, and unpasteurized juice carry similar risks. Raw sprouts (alfalfa, clover, radish, mung bean) are another common source of harmful bacteria. Wash all fruits and vegetables thoroughly.
Alcohol has no known safe amount during pregnancy. It raises the risk of miscarriage, stillbirth, and fetal alcohol syndrome, which can affect facial development and cognitive function. Caffeine crosses the placenta, and while its effects on the baby aren’t fully clear, most guidelines suggest limiting intake.
Exercise During Pregnancy
Staying active during pregnancy is not just safe for uncomplicated pregnancies, it’s actively beneficial. Current guidelines recommend at least 150 minutes of moderate-intensity aerobic activity per week, spread across multiple days. Walking, swimming, stationary cycling, and prenatal yoga all fit the bill. If you were already doing vigorous exercise before pregnancy, you can generally continue.
Research shows that exercising 30 to 60 minutes, two to seven times per week, is associated with a lower risk of gestational high blood pressure and cesarean delivery. For people who are overweight or obese, regular aerobic exercise during pregnancy is linked to a reduced chance of preterm birth. Activities with a high risk of abdominal impact or falls should be avoided, along with scuba diving, which can cause dangerous bubble formation in the baby’s circulation.
Mental Health Screenings
Depression and anxiety don’t wait until after delivery to appear. Prenatal anxiety and depression are common and treatable, but they often go unrecognized. Current recommendations call for mental health screening at the initial prenatal visit, again later in pregnancy, and at postpartum visits. These screenings use standardized questionnaires that take just a few minutes to complete and should be scored before you leave the appointment so any concerns can be addressed right away.
If you notice persistent sadness, excessive worry, loss of interest in things you used to enjoy, or difficulty functioning day to day, bring it up with your provider rather than waiting for the next screening. Pregnancy hormones can amplify mood changes, and support is available at every stage.
Warning Signs That Need Immediate Attention
Most pregnancy symptoms are uncomfortable but harmless. A few, however, signal something that needs urgent medical care. Seek help right away if you experience any of the following:
- Severe headache: one that won’t go away, worsens over time, or comes with blurred vision or dizziness
- Vision changes: flashes of light, bright spots, blind spots, or double vision
- Extreme swelling: swelling of the hands or face severe enough to make it hard to bend your fingers or open your eyes
- Vaginal bleeding: heavy bleeding that soaks through a pad, passing large clots, or foul-smelling discharge
- Severe belly pain: sharp, stabbing, or cramp-like pain that worsens over time
- Decreased fetal movement: a noticeable stop or slowing of the baby’s usual movement pattern
- Trouble breathing: sudden shortness of breath, chest tightness, or difficulty breathing while lying down
- Fever of 100.4°F or higher
- Leg pain or swelling: redness, swelling, or pain in one calf, which can indicate a blood clot
- Thoughts of self-harm: feeling hopeless or having thoughts about harming yourself or your baby
Many of these overlap with signs of preeclampsia, a condition involving dangerously high blood pressure that typically develops after 20 weeks. The combination of severe headache, vision changes, and sudden facial swelling is especially important to recognize. Preeclampsia can progress quickly and requires prompt treatment.
Your Prenatal Visit Schedule
For a straightforward pregnancy, the standard visit pattern is once a month from weeks 4 through 28, twice a month from weeks 28 through 36, and weekly from week 36 until delivery. High-risk pregnancies may require more frequent monitoring. Each visit typically includes a blood pressure check, a urine test, measurement of your belly, and a chance to hear the baby’s heartbeat. The increasing frequency toward the end isn’t cause for alarm; it’s simply how providers keep a close eye on things as the due date approaches.