Emily is 31. She's an interior architect, lives in Bristol with her partner Tom, and on that particular morning — a Thursday in March, to be precise — she's staring at a pregnancy test balanced on the edge of the bathroom sink. Two lines. She already knew, somewhere. The missed period, the tender breasts, that strange fatigue that hit her at three o'clock every afternoon. But seeing those two lines is something else entirely. It's the moment when the abstract becomes real. When "maybe one day" becomes "now."
And immediately after the euphoria — or the shock, or both — the same question millions of women before her have asked: "So what happens next?"
This guide is the most complete answer we can give you. Week by week, from the very first moment to birth, we'll walk through what your body is going through, what your baby is becoming, which appointments await you, and which practical tips can help you live this period with confidence.
Important note: in the UK, pregnancy is typically dated from the first day of your last menstrual period (LMP), meaning your pregnancy officially begins about two weeks before conception actually occurred. Most healthcare professionals and this guide use this dating system — so "week 4" means four weeks since your last period, even though your baby is only about two weeks old.
Your pregnancy, step by step
First trimester: the great beginning (weeks 1 to 13)
Weeks 1-2: before it even begins
Technically, you're not yet pregnant. Weeks 1 and 2 correspond to the period between your last period and ovulation. Your body is preparing: the endometrium thickens, the dominant follicle matures in the ovary, oestrogen levels rise gradually.
If you're trying to conceive, this is when folic acid is crucial. The NHS recommends 400 micrograms daily, ideally started at least one month before conception and continued until week 12. Folate plays a critical role in the closure of the neural tube — a process that occurs before most women even know they're pregnant.
Weeks 3-4: fertilisation and implantation
The egg meets the sperm — usually in the outer third of the fallopian tube. Within 24 hours, the genetic material fuses. The baby's sex is already determined. Everything is set, and you probably don't know yet.
The fertilised egg divides as it travels to the uterus: 2 cells, then 4, then 8, then a cluster called a morula, then a blastocyst. Around day 7 after fertilisation, it implants in the uterine lining — this is implantation. Some women experience light spotting (implantation bleeding), often mistaken for an early period.
The trophoblast — the outer layer of the blastocyst — begins producing hCG (human chorionic gonadotrophin). This is the hormone pregnancy tests detect.
When to test Modern home pregnancy tests are reliable from the first day of a missed period (around week 4-5). Testing too early can give a false negative — hCG levels may not be high enough yet. If in doubt, a blood test (quantitative hCG at your GP) is reliable from about 10 days after conception. The NHS advises testing from the first day of your missed period for the most accurate result.
Weeks 5-6: the heart begins to beat
The embryo measures about 2mm — the size of a sesame seed. But extraordinary things are happening at this scale. Cells differentiate into three layers that will give rise to every organ: the ectoderm (skin, brain, nervous system), mesoderm (muscles, bones, heart, blood vessels), and endoderm (digestive system, lungs).
Between weeks 5 and 6, the primitive heart tube begins to pulse. It's not a heart yet — it's a tube that beats — but it's the first functioning organ. On an early scan (often performed if there's bleeding or pain), this heartbeat is visible from week 6 in most embryos.
On the maternal side, symptoms set in: nausea (in 70-80% of women), intense fatigue, tender and painful breasts, heightened sensitivity to smells. These symptoms are caused by the rapid rise of hormones — particularly hCG and progesterone.
Weeks 7-8: the embryo takes human form
The embryo now measures 10-14mm. Limb buds appear — the beginnings of arms and legs. The face forms: eye spots, nostrils, mouth. The brain is developing at a breathtaking pace — 250,000 neurons per minute.
This is often when you book your first midwife appointment. Your booking appointment (ideally before week 10) confirms the pregnancy, initiates your antenatal care pathway, and calculates your estimated due date.
Substances to avoid completely The first trimester is the most critical period for embryonic development. Organs form between weeks 4 and 12 — this is organogenesis, when the embryo is most vulnerable to teratogenic agents. Alcohol (zero alcohol, no exceptions — foetal alcohol spectrum disorder has no safe threshold), tobacco, cannabis, and any medication not approved by your GP or midwife must be avoided. If you're on long-term medication, never stop abruptly without medical advice — some medications are more dangerous to stop suddenly than to continue under supervision.
Weeks 9-12: the end of embryogenesis
At week 9, the embryo officially becomes a foetus — all major organs are formed (even if they're not yet functional). It measures 3-4cm and weighs about 10 grams. Fingers and toes separate. The face is recognisable. The foetus is already moving — reflex movements, imperceptible to you.
Week 12 marks a psychological turning point for many women: the risk of miscarriage drops considerably (from about 15-20% in the first trimester to less than 1% in the second). Many women choose this moment to share the news.
This is also the time for the dating scan (between weeks 10 and 14), one of the most important examinations of pregnancy. It dates the pregnancy accurately, checks the number of embryos, and measures the nuchal translucency — a marker that, combined with a blood test, assesses the risk of Down's syndrome.
Weeks 13-15: the transition
The foetus measures 8-10cm. Nausea begins to fade for most women (though for some it persists longer, and that's normal). Energy gradually returns. Your bump begins to show — subtly, imperceptibly to others, but you feel it. Clothes start to feel tight.
Dealing with nausea Eat little and often (5-6 small meals rather than 3 large ones), avoid an empty stomach (keep plain biscuits by your bedside), favour cold foods (less aromatic), and try fresh ginger (its effectiveness is supported by several studies — a teaspoon of grated ginger in hot water). If nausea is severe (multiple vomiting episodes, weight loss), seek medical help: hyperemesis gravidarum is a real condition affecting 1-2% of pregnancies that requires medical treatment.
Second trimester: the bloom (weeks 14 to 27)
Weeks 16-20: first movements
The foetus measures 14-16cm and weighs about 200g. Its proportions are changing — the head, which made up half the body in the first trimester, is harmonising. Lanugo — a fine downy hair — covers its entire body. It's drinking amniotic fluid and urinating — the kidneys are starting to function.
And then, one day, between weeks 18 and 22 (earlier if it's a second pregnancy, later if it's your first), you feel it. The first foetal movements. It's not a kick — not yet. It's more of a flutter, a bubble popping, a butterfly beating its wings in your belly. It's subtle. And it's a moment every mother describes as one of the most moving of her life.
Weeks 20-24: the anomaly scan
The mid-pregnancy scan (between weeks 18 and 21 in the NHS) is the most detailed examination of your pregnancy. The sonographer checks, organ by organ, the foetus's development: brain, heart (all four chambers), spine, kidneys, limbs, face. It's a thorough, methodical examination lasting 20-30 minutes.
This is often when parents who wish to can learn the baby's sex — the genitals are sufficiently developed to be identified reliably.
The foetus measures about 25-30cm and weighs 500-600g. It can hear sounds — your voice, your heartbeat, external noises. Studies have shown that newborns recognise their mother's voice and prefer music they heard in utero. If you talk to your baby, it hears you. This is scientifically proven.
When to worry about movements If you don't feel movements before week 22 in a first pregnancy, that's not unusual — the position of the placenta (an anterior placenta "cushions" movements) and your build play a role. However, after week 28, if you notice a distinct decrease in your baby's usual movement pattern, contact your maternity unit. Tommy's recommends getting to know your baby's normal pattern and reporting any changes — never wait until the next day.
Weeks 25-28: viability
Weeks 24-25 mark the threshold of viability — the stage from which a baby born prematurely can survive with neonatal intensive care. This threshold is a medical landmark, not a sharp boundary: survival rates and outcomes improve significantly with every additional week in utero.
The foetus weighs about 1kg at week 28. Its brain is developing extraordinarily rapidly — folds and convolutions are forming, neural connections multiplying. Its eyes open. It alternates between sleep and waking — you'll notice its activity follows a pattern, often more intense in the evening (when you're resting and your walking no longer rocks it to sleep).
Gestational diabetes screening Between weeks 24 and 28, your midwife may offer a glucose tolerance test (GTT) if you have risk factors (BMI over 30, previous gestational diabetes, family history, South Asian/Black Caribbean/Middle Eastern heritage). Gestational diabetes affects 4-5% of pregnancies in the UK. Untreated, it can lead to a large baby (macrosomia), birth complications, and increased risk of type 2 diabetes for the mother later. Well managed (dietary changes, sometimes insulin), it poses no serious danger — but it must not be ignored.
Third trimester: the final stretch (weeks 28 to 40+)
Weeks 29-32: baby gains weight
The foetus enters its final growth phase. It weighs about 1.5kg at week 30 and will gain approximately 200-250 grams per week until birth. Subcutaneous fat accumulates — this will give it those round newborn cheeks and regulate its temperature after birth.
A growth scan may be offered around weeks 32-36 to check the baby's size, position, amniotic fluid levels, and placental position. If the baby is in breech position (bottom down), external cephalic version (ECV) may be offered — but many babies turn spontaneously before week 36.
On the maternal side, discomforts accumulate: breathlessness (the uterus compresses the diaphragm), heartburn, frequent urination (the baby's head presses on the bladder), sleep disturbances, Braxton Hicks contractions (irregular, painless "practice" contractions). It's physically demanding. Allow yourself rest without guilt.
Weeks 33-36: lung maturation
The baby's lungs are producing surfactant — an essential substance that prevents the air sacs from collapsing between breaths. Lung maturation is the key factor in viability: a baby born at week 34 with mature lungs has excellent prospects, while one without sufficient surfactant will need respiratory support.
This is when you pack your hospital bag, finalise your birth preferences, and may tour the maternity unit. It's also the time for antenatal classes — whether NHS classes, hypnobirthing, pregnancy yoga, or active birth workshops.
Hospital bag essentials For baby: 6 vests, 6 sleepsuits, 2 hats, nappies (size 1), cotton wool (not wipes for the first few days), a blanket. For you: 2 front-opening nightdresses or tops (for feeding), large comfortable pants, maternity pads, toiletries, your notes and birth preferences. Pack by week 34 — babies don't always have a sense of timing.
Weeks 37-40+: full term
At week 37, the baby is considered "early term," and at 39 weeks "full term" — meaning it can be born without prematurity risks. It measures about 48-52cm and weighs 2.8-3.5kg on average. Its head engages in the pelvis — you may feel a "lightening" sensation, pelvic pressure, and paradoxically, easier breathing (as the diaphragm is freed).
Your estimated due date (EDD) is set at 40 weeks. Only 4% of babies arrive exactly on their due date. Most are born between weeks 38 and 42. "Post-term" begins at 42 weeks — beyond this, the placenta ages and functions less efficiently, and induction is routinely offered. NICE recommends offering induction between 41 and 42 weeks.
Signs that labour is approaching: a "show" (the mucus plug — a thick, sometimes blood-streaked mucus that can come away hours or days before labour), regular painful contractions (unlike Braxton Hicks, these increase in frequency and intensity), and waters breaking (a continuous flow of clear fluid — not always the dramatic gush films portray).
When to go to hospital The classic guidance: regular contractions every 5 minutes, lasting about 60 seconds, for at least an hour (for a first baby). For subsequent pregnancies, go sooner — labour is often faster. If your waters break, contact your maternity unit within the hour, even without contractions. And in case of heavy bleeding, severe abdominal pain, or a sudden reduction in baby's movements: go to hospital immediately, without hesitation.
Your antenatal care schedule
The NHS provides comprehensive antenatal care throughout pregnancy. Here's the schedule recommended by NICE guidelines.
Weeks 8-12: Booking appointment with your midwife. Medical history, blood tests (blood group, rhesus status, iron levels, sickle cell/thalassaemia screening, HIV, hepatitis B, syphilis, rubella immunity), urine test. Discussion of screening options for Down's, Edwards', and Patau's syndromes.
Weeks 10-14: Dating scan (first ultrasound). Combined screening test for chromosomal conditions (nuchal translucency measurement + blood test).
Week 16: Antenatal appointment. Review screening results. Blood pressure and urine check.
Weeks 18-21: Anomaly scan (second ultrasound — the "20-week scan"). Detailed check of all baby's organs and structures.
Week 25: Antenatal appointment (first pregnancy only). Blood pressure, urine, fundal height measurement.
Week 28: Antenatal appointment. Blood tests (haemoglobin, antibodies). Anti-D injection if you're rhesus negative. Glucose tolerance test if indicated.
Weeks 31-34: Antenatal appointments. Growth assessment. Discussion of birth plan.
Weeks 36-40: Weekly or fortnightly appointments. Baby's position checked. Group B Streptococcus (GBS) discussed. Membrane sweep offered from 40 weeks.
Week 41+: Induction discussed and offered. Monitoring of baby's wellbeing.
NHS maternity care All NHS antenatal and postnatal care is free, including scans, blood tests, midwife appointments, and hospital birth. You're entitled to free NHS dental care during pregnancy and for 12 months after your due date (apply for a maternity exemption certificate through your midwife). Statutory maternity pay is 90% of average weekly earnings for the first 6 weeks, then £172.48/week (or 90% if lower) for the remaining 33 weeks. Shared parental leave allows partners to share up to 50 weeks.
Warning signs: when to seek urgent help
The vast majority of pregnancies proceed without complications. But certain symptoms should prompt you to seek help quickly — not next week, not tomorrow, now.
Vaginal bleeding: In the first trimester, it may be benign (implantation bleeding, cervical sensitivity) or signal a miscarriage or ectopic pregnancy. In the third trimester, bleeding can indicate placenta praevia or placental abruption — both obstetric emergencies.
Severe abdominal pain: Sharp, localised pain, different from normal stretching sensations, can signal an ectopic pregnancy (first trimester) or placental abruption (third trimester).
Fluid leaking: A continuous flow of clear fluid, even in small amounts, should take you to your maternity unit. Premature rupture of membranes carries an infection risk.
Reduced foetal movements: After week 28, if you notice your baby is moving distinctly less than usual, contact your maternity unit that day. Monitoring will check that all is well. Never wait and see — Tommy's research shows reduced movements can be an important warning sign.
Severe headache + visual disturbance + sudden swelling: These signs together can suggest pre-eclampsia — a serious complication related to high blood pressure. This is an emergency.
Temperature above 37.5°C with other symptoms: Fever during pregnancy can signal an infection (urinary, listeriosis) requiring prompt treatment.
The key message When in doubt, call your maternity unit. The midwives on the triage line are there precisely for this — to assess, reassure, or act. A "just in case" visit is always better than a complication detected too late. No healthcare professional will ever fault you for seeking reassurance.
Preparing for arrival: the real essentials
The baby industry would have you believe you need 347 items to welcome a newborn. The reality: a newborn needs warmth, food, cleanliness, and you. That's it.
The true essentials: a safe sleep space (Moses basket or cot with a firm mattress, no pillows, no duvets, no bumpers — Lullaby Trust safe sleep guidelines), vests and sleepsuits (cotton, newborn + 0-3 months), nappies, cotton wool and water (or a gentle cleanser), an i-Size car seat (required to leave hospital by car), and a way to feed your baby (breast or bottles + formula).
What can wait: the bouncer, the pram (a sling works brilliantly for the first weeks), the changing table (a towel on a bed works fine), the baby monitor (if you're in a flat), and everything that's "lovely but not vital" — musical mobile, smart nightlight, top-of-the-range bottle warmer.
Birth preferences: this is a document expressing your wishes for labour and birth — positions, pain relief preferences, skin-to-skin, feeding intentions, who you'd like present. It's not a contract — it's a conversation starter with your care team. Most NHS trusts actively encourage this. Write it with your partner, discuss it with your midwife, and keep it flexible — birth is by nature unpredictable.
The postnatal period: the forgotten chapter We prepare for birth — rarely for the homecoming. Yet the first weeks with a newborn are intense, physically and emotionally. Batch-cook and fill the freezer, accept (demand!) help from family and friends, and know that the "baby blues" (days 3-5 after birth, caused by hormonal shifts) affects 50-80% of women. If it lasts more than two weeks or involves dark thoughts, detachment from the baby, or persistent anxiety, speak up: this may be postnatal depression, which affects 10-15% of mothers and responds very well to treatment when caught early. Your health visitor is trained to spot the signs — let them help.
Frequently asked questions about pregnancy
How is my due date calculated?
Your estimated due date (EDD) is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period. The dating scan (weeks 10-14) refines this estimate by measuring the crown-rump length of the embryo, which is the most reliable marker. Only 4% of babies arrive exactly on their due date — most are born within the two weeks either side.
Can I exercise during pregnancy?
Yes, and it's actively encouraged by the NHS and RCOG, unless you have a medical contraindication (threatened premature labour, placenta praevia, severe pre-eclampsia). Recommended activities include: walking, swimming, pregnancy yoga, stationary cycling. Activities to avoid: contact sports, sports with fall risk (horse riding, skiing), scuba diving. Aim for 150 minutes of moderate activity per week — enough to raise your heart rate and break a light sweat.
Is nausea in the first trimester normal?
Yes, 70-80% of pregnant women experience nausea in the first trimester, typically between weeks 6 and 14. It's caused by the rapid rise in hCG hormone. It's unpleasant but not dangerous — except in cases of hyperemesis gravidarum (severe vomiting with dehydration and weight loss), which affects 1-2% of pregnancies and requires medical treatment. The NHS Pregnancy Sickness Support helpline can provide guidance.
What foods should I avoid during pregnancy?
Raw or undercooked meat, fish, and eggs (risk of salmonella, toxoplasmosis, listeriosis); unpasteurised dairy products; mould-ripened soft cheeses (brie, camembert) and blue cheese; shark, swordfish, and marlin (high mercury); liver and liver products (excess vitamin A); pâté; alcohol (zero, with no exceptions — there is no safe level). Salads and fruits should be thoroughly washed. Check the NHS website for the complete and current list.
When should I announce my pregnancy?
There's no rule — it's entirely your choice. The tradition of waiting until 12 weeks comes from the fact that miscarriage risk drops significantly after the first trimester. Some women prefer to wait for the dating scan for reassurance. Others share the news from the positive test. It's also perfectly valid to tell close family and friends early — if something goes wrong, having support matters. There is no "right" time.
Do I have to have an epidural?
No, an epidural is entirely your choice. In the UK, about 40% of women having a vaginal birth use an epidural. Alternatives include: gas and air (Entonox), TENS machine, water birth, breathing techniques, hypnobirthing, pethidine/diamorphine injection. Many women use a combination. Your midwife will discuss all options with you, and you can change your mind at any point during labour — including requesting an epidural if you initially planned without one.
What maternity leave am I entitled to in the UK?
In the UK, statutory maternity leave is up to 52 weeks (26 ordinary + 26 additional). Statutory Maternity Pay (SMP) is paid for 39 weeks: 90% of average weekly earnings for the first 6 weeks, then £172.48/week (or 90% if lower) for the remaining 33 weeks. You must give your employer at least 15 weeks' notice before your due date. Shared Parental Leave allows you to share up to 50 weeks of leave and 37 weeks of pay with your partner.