Stages of Pregnancy: What to Expect
Forty weeks sound like a long time until you're in it. Pregnancy is usually divided into three trimesters, and each one has its own rhythm, its own set of changes, worries, and small milestones worth celebrating. Here's a plain-language guide to what's happening and when.
First Trimester (Weeks 1–13)
What's happening inside
This is the building phase. Within the first eight weeks, a fertilized egg becomes an embryo with a beating heart, a developing brain and spinal cord, and the beginnings of arms and legs. By the end of week 12, all major organs have formed — your baby is now called a fetus.
Size check: Poppy seed at 4 weeks → raspberry at 8 weeks → plum at 12 weeks (about 2 inches, half an ounce).
What you might feel
- Fatigue that naps don't quite fix
- Nausea, with or without vomiting (the "morning" part is a lie — it can hit any time)
- Tender, heavier breasts
- Frequent trips to the bathroom
- Food aversions or sudden strong cravings
- Mood swings, thanks to a hormonal surge
Your to-do list
Joy A. Leong MD, OBGYN at PIH Health says, "Book your first prenatal appointment, ideally around week 8. Start a prenatal vitamin with folic acid if you haven't already. Stop alcohol, smoking, and recreational drugs, and check with your provider before taking any medication or supplement, including over-the-counter ones".
Good to know: Roughly 70–80% of pregnant people experience nausea in the first trimester. It usually eases by week 14. If you can't keep fluids down, call your provider — that's treatable, not something to tough out.
Second Trimester (Weeks 14–27)
What's happening inside
Often called the "golden trimester," and for good reason, nausea typically fades and energy returns. Your baby grows fast: fingerprints form, hair appears, and the ears become functional enough to hear your voice. Somewhere between weeks 18 and 22, you'll likely feel the first flutters of movement, called quickening.
Size check: Avocado at 16 weeks → banana at 20 weeks → ear of corn at 24 weeks → head of cauliflower at 27 weeks (about 14 inches, 2 pounds).
What you might feel
- More energy and a returning appetite
- A visible bump (and the end of hiding it)
- Round ligament pain, sharp twinges along the sides of your belly
- Heartburn, constipation, or both
- Backaches as your center of gravity shifts
- Stretch marks, darkening skin patches, or a line down your abdomen
What sleep looks like now
This is usually when back-sleeping starts to feel uncomfortable — and there's a reason. As your uterus grows, lying flat can press on the large vein returning blood to your heart, which may leave you lightheaded. Side-sleeping is the recommendation from roughly the midpoint of pregnancy onward, often with a pillow behind your back and one between your knees. If you wake up on your back, don't panic. Just roll over.
Your to-do list
You'll have your anatomy scan around week 20, a detailed ultrasound checking growth and organ development, and often where you can learn the sex if you want to. Between weeks 24 and 28, expect a glucose test for gestational diabetes. This is also the sweet spot for touring birth facilities, starting childbirth classes, and telling your employer.
Third Trimester (Weeks 28–40+)
What's happening inside
Everything now is about maturing and gaining weight. The lungs are the last major system to finish developing. Your baby's bones harden; they begin cycling through sleep and wake states, and sometime in the final weeks they'll likely shift head-down in preparation for birth.
Size check: Butternut squash at 32 weeks → honeydew melon at 36 weeks → small pumpkin at 40 weeks (roughly 19 to 21 inches and 6 to 9 pounds, with a wide healthy range).
What you might feel
- Shortness of breath as your uterus presses upward
- Swelling in your feet, ankles, and hands
- Trouble sleeping and needing the bathroom constantly
- Braxton Hicks contractions, irregular practice tightening
- Pelvic pressure and lightning-fast fatigue
- Leaking colostrum from your breasts
Other signs of labor are genuinely starting: your water breaking (a gush or a persistent trickle), a mucus discharge that may be tinged pink or brown, and steady downward pressure.
A common guideline is the 5-1-1 rule, contractions every 5 minutes, lasting 1 minute each, for 1 hour. But ask your provider for their specific instructions, since it varies with your history and how far you live from your birth facility. And call sooner, without hesitation, if your water breaks or you notice bleeding.
Your to-do list
Prenatal visits get more frequent, every two weeks, then weekly near the end. Pack your hospital bag by week 36. Finalize your birth preferences, install the car seat, and line up help for the first few weeks postpartum.
The Fourth Trimester (Birth to ~12 Weeks Postpartum)
Most pregnancy guides stop at delivery. That leaves out the stage many parents find hardest, the one where you're recovering from a major physical event while caring for a newborn on almost no sleep.
What recovery actually looks like
Bleeding and discharge, called lochia, taper over several weeks. Cramping continues as your uterus shrinks back down. Add night sweats, constipation, sore breasts as milk comes in, hair shedding around the three-month mark, and whether you delivered vaginally or by cesarean, real tissue healing that takes time.
Emotionally
The "baby blues" affect most new parents: weepiness, irritability, and feeling overwhelmed in the first two weeks. When those feelings deepen, last longer, or make it hard to function or care for your baby, that's postpartum depression or anxiety, common and very treatable. It is not a character flaw or a parenting verdict.
Don't wait for the six-week visit. Current guidance favors contacting your provider within the first three weeks, with a full check by twelve. If something feels wrong before then, call.
Postpartum warning signs — get help immediately:
- Bleeding that soaks a pad in an hour or less, or passing large clots
- Fever over 100.4°F (38°C)
- A severe headache, vision changes, or swelling in your face and hands
- Chest pain or trouble breathing
- Pain, redness, or swelling in one leg
- Any thoughts of harming yourself or your baby
The National Maternal Mental Health Hotline is available around the clock at 1-833-TLC-MAMA (1-833-852-6262). You don't need to be in crisis to call.
When to Call Your Provider Right Away
Some symptoms need prompt attention at any stage of pregnancy:
- Vaginal bleeding or fluid leaking
- Severe or persistent abdominal pain
- A bad headache that won't go away, blurred vision, or sudden swelling in your face and hands
- Fever over 100.4°F (38°C)
- Painful urination
- After 28 weeks: a noticeable drop in your baby's movement
- Regular, painful contractions before 37 weeks
- Trust your instincts. Providers would much rather hear from you about something that turns out to be nothing.
Frequently Asked Questions
What foods should I avoid while pregnant?
Skip raw or undercooked meat, fish, and eggs; unpasteurized milk, soft cheeses, and juice; raw sprouts; and high-mercury fish (shark, swordfish, king mackerel, tilefish, and bigeye tuna). Deli meats and hot dogs are fine if heated until steaming. Alcohol is the one true no. There's no established safe amount. Meanwhile, low-mercury fish like salmon and canned light tuna are actively encouraged: two to three servings a week supports your baby's brain development.
How much caffeine is okay?
Most guidance puts the ceiling at about 200 mg a day, roughly one 12-ounce cup of coffee. Remember that tea, soda, chocolate, and energy drinks all count toward the total.
Can I take pain relievers?
Talk to your provider before taking anything, including over-the-counter medication. In general, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen are avoided in pregnancy, particularly after 20 weeks. Acetaminophen has been the subject of public debate recently; major obstetric organizations including American College of Obstetricians and Gynecologists (ACOG) continue to consider it appropriate when used at the lowest effective dose for the shortest time needed. Your provider knows your history and is the right person to make that call with you.
How much weight should I gain?
It depends on where you started. General guidance by pre-pregnancy BMI:
- Underweight (under 18.5): 28–40 lbs
- Healthy weight (18.5–24.9): 25–35 lbs
- Overweight (25–29.9): 15–25 lbs
- Obese (30+): 11–20 lbs
Carrying twins raises all of these. Gain also isn't evenly spread, the first trimester adds little, and most accumulates in the second and third. Your provider will set targets that fit you specifically.
For most uncomplicated pregnancies, yes, and it's beneficial. About 150 minutes a week of moderate activity is the standard recommendation. Walking, swimming, stationary cycling, and prenatal yoga are all good choices. Avoid contact sports, anything with a fall risk, scuba diving, and lying flat on your back for long stretches later on. A rough gauge: you should be able to hold a conversation while moving.
Is sex safe during pregnancy?
In an uncomplicated pregnancy, yes, right up until labor. Your baby is protected by the amniotic sac and your cervix, and can't be harmed or aware of it. Your provider may advise against it in specific situations, placenta previa, a history of preterm labor, or unexplained bleeding, so ask if you're unsure. Shifting libido in either direction throughout the trimesters is completely normal.
A Few Things Worth Remembering
Your due date is an estimate, not an appointment. Only about 1 in 20 babies arrive on the exact day predicted, and anything from 37 to 42 weeks is normal territory. Try not to measure your pregnancy against anyone else's, either: bumps grow differently, symptoms vary wildly, and someone else's easy first trimester says nothing about yours. And your mental health counts as prenatal care. Anxiety and depression during pregnancy are common and treatable, and they belong in your appointments just as much as your blood pressure does. Forty weeks is a long stretch, but you don't have to navigate it from memory or on your own. Bring your questions to the people whose job it is to answer them. To find an OBGYN near you, visit PIHHealth.org/Doctors.
