Pregnancy Week by Week: What to Expect Each Trimester

Pregnancy lasts around 40 weeks from the first day of your last menstrual period, but what actually happens week by week as you progress through each trimester? This guide walks you through pregnancy week by week — what to expect in your body, your baby's development, your finances, and your health across all three trimesters. Whether you're planning ahead or already pregnant, understanding each stage helps you prepare practically and emotionally.

First Trimester (Weeks 1–13): Early Changes and Hidden Drama

Pregnancy begins on the first day of your last menstrual period (LMP), even though conception happens around week 2. So when you're told you're "8 weeks pregnant," you're actually only 6 weeks past conception. Confusing? Yes. Universal across medicine? Also yes.

Weeks 1–4: Your body releases the hormone hCG (human chorionic gonadotropin), which stops your period and maintains the corpus luteum — the temporary gland that produces progesterone early in pregnancy. You might feel nothing, or you might feel everything: sore breasts, fatigue, nausea. If you want to understand hCG levels in early pregnancy in more detail, that's a natural next step.

Weeks 5–8: Morning sickness peaks (despite the name, it can hit any time). Your baby is the size of a lentil and developing at breakneck speed — heart, lungs, brain, limbs all forming. You're likely exhausted and possibly craving or hating foods you normally enjoy.

Weeks 9–13: The nausea often peaks around week 9, then gradually improves. Your baby is now called a fetus (no longer an embryo) and is roughly the size of a plum. Fingers and toes separate, facial features develop, and your baby can bend their arms and legs. You'll have your first routine ultrasound around week 11–13, often called the dating and nuchal translucency scan.

First trimester priorities:

Start folic acid supplementation immediately if you haven't already (400mcg daily for the first 12 weeks)
Book your antenatal care with your GP or midwife-led unit
Avoid alcohol, smoking, and unpasteurised dairy
Rest when you can — fatigue is real and expected

Second Trimester (Weeks 14–27): The "Honeymoon" Phase

The second trimester is when most women start to feel genuinely pregnant in a good way. Morning sickness usually fades, energy rebounds, and your baby becomes real in a tangible way.

Weeks 14–18: Morning sickness typically resolves. Your bump becomes visible — not just to you, but to the world. Your baby is about 15cm long and weighs roughly 150g. You might start feeling the baby move around week 16–20 (earlier if you've been pregnant before, later if this is your first).

Weeks 19–23: Your baby's sex can usually be seen on the anatomy scan (around week 20). Your baby is now 26cm long and weighs around 600g. Their movements are increasingly coordinated — practicing breathing motions, swallowing, and putting their hands to their face. You can see all this on ultrasound, which is why the 20-week scan feels genuinely magical.

Weeks 24–27: Your baby weighs around 1kg and is roughly 33cm long. Their lungs are developing, and if they were born now (though we hope they're not), they would have a chance of survival with intensive medical support. You're likely sleeping more, feeling increasingly clumsy, and noticing you can't see your feet anymore.

Second trimester priorities:

The 20-week anatomy scan screens for structural abnormalities
Continue or start prenatal exercise — 150 minutes of moderate activity per week is recommended and safe
Review your pregnancy nutrition and confirm you're getting enough iron, calcium, and vitamins
Think about maternity leave — you'll need to give formal notice soon (usually by week 15)

Third Trimester (Weeks 28–40+): The Home Stretch

The third trimester is when pregnancy gets visibly real. You're heavy, uncomfortable, your baby is pressing on your bladder, and labor is no longer theoretical.

Weeks 28–32: Your baby weighs 1–2kg and is around 40cm long. Their movements are strong and sometimes uncomfortable (elbows in your ribs, feet in your pelvis). You'll have more frequent antenatal appointments now. If you haven't already, discuss screening options with your midwife, especially if you're pregnant after age 35.

Weeks 33–36: Your baby is in the final growth sprint, gaining around 200g per week. They're running out of space, which is why their movements feel more like rolling and less like gymnastics. Around week 36, your midwife checks which way your baby is facing — head down is ideal for vaginal birth. If they're breech (bottom-first), you'll discuss options.

Weeks 37–40+: Your baby is now considered full-term. They weigh 3–3.5kg on average. You're probably tired of being pregnant. Any day now, your body will start labor — when it does, contractions become stronger, more regular, and closer together.

Third trimester priorities:

Antenatal appointments increase to every 2 weeks until week 36, then weekly
Have your "getting ready" conversations: where you'll give birth, who will be there, pain relief options
Arrange postpartum recovery support — you'll need help after birth, whether that's a partner, family, or paid help
Pack your hospital bag around week 36
Track your milestones so you don't miss important antenatal appointments

Financial Planning for Pregnancy and Childcare

Pregnancy itself is free on the NHS, but preparing for a baby's arrival costs real money. Here are the numbers:

Maternity/paternity leave and pay: Statutory maternity pay is 90% of your average weekly earnings for the first 6 weeks, then £184.03 per week (as of 2026) for the following 33 weeks. That's 39 weeks of partial income total. Many employers offer enhanced packages — check yours before your due date. Partners get 2 weeks of statutory paternity pay at the same flat rate.

Childcare: The average UK nursery costs £1,100–£1,400 per month full-time. The government's 30 hours free childcare (for 3–4 year olds of working parents) helps significantly, but doesn't kick in until age 3. Nannies cost £400–£600+ per week. Childminders typically charge £50–£70 per day per child. Build this into your budget now if you plan to return to work.

First-year baby costs: Budget £1,500–£3,000 for essentials:

Pram or pushchair: £400–£1,200
Car seat: £150–£400 (essential for hospital discharge)
Cot and mattress: £100–£400
Clothing (newborn through 12 months): £300–£600
Nappies and wipes (for 12 months): £600–£1,200
Other items (changing table, steriliser, bottles if bottle-feeding): £300–£600

Buy second-hand where safety standards allow (clothes, toys, books). Buy new where they matter (car seats, mattresses, helmets).

Medium-term planning: The cost of raising a child from birth to age 18 is estimated at £150,000–£200,000 in the UK, or £200,000–£250,000+ in London. That's roughly £700–£1,100 per month on average. Not all of that is discretionary — schools, healthcare, and basic food are there. But it's real money to factor into your financial plan. Use our fertility and planning tools to set savings targets and track progress before baby arrives.

Health, Nutrition, and Wellness During Pregnancy

Vitamins and supplements: NHS vitamin guidance recommends:

Folic acid: 400mcg daily from before conception through the first 12 weeks
Vitamin D: 10mcg daily throughout pregnancy and breastfeeding
Iron: if your midwife's blood tests show you need it (around 30% of pregnant women do)
Iodine, calcium, and choline: if your diet is low in these (ask your midwife)

Folic acid in particular is important — deficiency is linked to neural tube defects. Start supplementation before conception if you're planning pregnancy.

Exercise during pregnancy: Safe and recommended unless your midwife says otherwise. Aim for 150 minutes of moderate activity per week — the same as non-pregnant adults. Walking, swimming, and prenatal yoga are popular. Avoid contact sports, heavy lifting, and activities with a fall risk. Pregnancy-safe exercise maintains fitness, can ease labor, and supports postpartum recovery.

Weight gain: The recommended gain depends on your pre-pregnancy BMI. A healthy-weight woman (BMI 18.5–24.9) should gain 11.5–16kg over the full pregnancy. An underweight woman might gain more; an overweight woman might gain less. Check your starting point with a BMI calculator if you're unsure, then discuss your target with your midwife.

Screening and monitoring: You'll have two routine ultrasounds — the dating scan (weeks 11–13) and the anatomy scan (week 20). Additional screening depends on age, health, and results of these first scans. Discuss your individual options with your midwife.

Frequently Asked Questions

Q: When should I tell people I'm pregnant? A: There's no right answer. Many wait until week 12 when miscarriage risk drops significantly. Others tell people immediately. Tell whoever you'd want support from if something went wrong.

Q: Will I need intervention during birth? A: Most births are straightforward, but about 1 in 4 have intervention (induction, instrumental delivery, cesarean). Your age, health history, and how labor progresses determine this. Discuss your preferences and history with your midwife in advance. NHS guidance on labor and birth covers your options.

Q: What's a normal weight gain in pregnancy? A: It depends on your pre-pregnancy BMI. A healthy-weight woman (BMI 18.5–24.9) gains 11.5–16kg total. An underweight woman (BMI <18.5) might gain 12.5–18kg. An overweight woman (BMI 25–29.9) might gain 7–11.5kg. Your midwife will review this at each visit and adjust expectations based on your individual circumstances.

Q: Is it safe to fly while pregnant? A: Generally yes, between weeks 14–27. After week 28, many airlines restrict flights. Deep vein thrombosis (blood clots) is a real but small risk on long flights. Get up and walk around every few hours if you fly.

Q: Can I eat soft cheese, deli meat, and sushi? A: Soft unpasteurised cheeses (brie, feta, blue cheese) carry a small listeria risk — avoid them. Cooked deli meats are fine; cured/smoked meats (prosciutto, salami) carry a small toxoplasmosis risk if raw. Sushi with cooked fish is fine; raw fish carries a small food poisoning risk — your choice. NHS pregnancy nutrition guidance has a full food safety list.

Q: What happens if I go past my due date? A: Most due dates are rough estimates (within ±2 weeks). Doctors typically induce labor at 10–14 days past your due date. This isn't immediate emergency — induction itself carries risks, so this is a discussion with your medical team based on your individual factors.

Q: How do I know if I'm in labor? A: Early labor contractions are 15–20 minutes apart and don't stop when you move. They gradually get stronger and closer together. If you're leaking fluid, bleeding heavily, or your baby stops moving, call your maternity unit immediately. Otherwise, you have time.

Q: Why does pregnancy last 40 weeks if I only conceive at week 2? A: Medical dating counts from the first day of your last menstrual period, not conception. This standard makes it easier to date pregnancy early (you know when your period was; you don't know exactly when you conceived). So "9 weeks pregnant" means 9 weeks since your LMP, but your baby is only 7 weeks old. This universalizes dating across all pregnancies.

What's Next

Pregnancy is long — 40 weeks is nearly 10 months. By understanding what to expect week by week across each trimester — both in your body and in your baby's development — you can prepare practically without being blindsided by normal changes.

The financial side often surprises people: maternity pay drops, childcare costs are real, and the first few years of raising a child are genuinely expensive. Use our fertility and planning tools to budget these realities. Book your antenatal care early, stay consistent with supplements, and reach out to your midwife whenever something doesn't match what's in here.

Your midwife and GP are your experts. This guide is a map; they're your navigation.