Your Complete 40-Week Pregnancy Guide

Understanding Your Three Trimesters

Pregnancy is divided into three trimesters, each roughly thirteen weeks long. Knowing what to expect at each stage — not just physically but emotionally and clinically — is what allows you to move through pregnancy with informed confidence rather than reactive anxiety.

First trimester (weeks 1–12)

The most biologically intense period of the pregnancy, and also the one that happens most invisibly. Rapid cell division, organ formation, placenta development, and the dramatic rise and plateau of hCG all occur in these twelve weeks. Most of the classic pregnancy symptoms — nausea, fatigue, breast tenderness — are driven by this hormonal activity and typically ease as hCG levels stabilise toward the end of the trimester.

Second trimester (weeks 13–27)

Often called the golden trimester, and for many people the description fits. hCG levels plateau, which usually means nausea eases and energy returns. The bump becomes externally visible — generally around weeks 16–20 in a first pregnancy — and the anomaly scan at weeks 18–21 provides the most detailed structural picture of your baby's development. Somewhere between weeks 16 and 22, most people feel fetal movements for the first time. This is often the most comfortable and settled period of the whole pregnancy.

Third trimester (weeks 28–40)

The final stretch. Your baby is now gaining weight rapidly — around 250 grams per week from week 32 — and their position in the uterus becomes increasingly relevant as you approach term. Appointments become more frequent, common discomforts like pelvic girdle pain and heartburn tend to peak, and many people find nesting instincts arrive strongly in weeks 36–40. Labour can begin at any point from week 37, which is full term.

Physical Changes and Common Symptoms by Trimester

Pregnancy affects virtually every system in your body. The key is knowing which changes are expected and which are signals that something needs attention.

First trimester

• Nausea and vomiting — affects around 80% of pregnancies, typically peaking at 8–10 weeks. Severe vomiting (hyperemesis gravidarum) requires medical treatment.
• Fatigue — your body is building the placenta. The tiredness is physiological and profound.
• Breast changes — tenderness, fullness, and darkening of the areola, driven by rising hormones.
• Light spotting — common at implantation, but any bleeding worth reporting to your midwife or EPU.

Second trimester

• Round ligament pain — sharp twinges in the lower abdomen as the uterus expands. Brief, positional, and normal.
• Braxton Hicks contractions — practice contractions that become more noticeable from around week 20. Irregular and usually painless.
• Fetal movement (quickening) — first felt between weeks 16–22. Initially subtle and easily confused with digestive sensations. By week 28, you should have a clear sense of your baby's daily pattern.
• Skin changes — linea nigra, melasma, and stretch marks are all normal hormonal responses.

Third trimester

• Pelvic girdle pain (PGP) — affects around 20% of pregnancies. Physiotherapy referral is available through your midwife and is worth asking for early.
• Heartburn — the growing uterus pushes against the stomach. Small frequent meals and sleeping slightly propped up both help.
• Oedema — mild symmetrical swelling of the feet and ankles is normal, especially in warm weather. Sudden severe swelling — particularly of the face or hands — is a pre-eclampsia warning sign that needs immediate assessment.
• Breathlessness — the uterus presses against the diaphragm. This usually eases when the baby's head engages lower in the pelvis.

Your NHS Antenatal Appointments and Scans

The NHS provides a structured schedule of antenatal care throughout your pregnancy. Understanding what each appointment covers means you can arrive prepared, with questions ready, rather than processing information cold under time pressure.

Booking appointment (weeks 8–10)

Your first midwife appointment is the longest — typically 60–90 minutes. It covers your complete health and family history, blood tests (including blood group, rhesus factor, HIV, hepatitis B and C, syphilis, sickle cell and thalassaemia screening), urine testing, blood pressure, BMI, and a mental health check. You leave with your maternity notes, which you should carry with you everywhere from now on.

Dating scan (weeks 11–14)

Crown-to-rump measurement confirms your gestational age and due date. The scan also measures nuchal translucency and, combined with blood test results, provides first trimester screening for chromosomal conditions including Down's syndrome. This is screening, not diagnosis — the result tells you a probability, not a certainty.

Anomaly scan (weeks 18–21)

The most detailed structural assessment of your baby — a systematic check of the brain, face, spine, heart, abdominal organs, limbs, and placenta. It takes around 30 minutes, and sonographers typically focus rather than narrate. Bring questions written down; you may not think clearly in the moment.

Appointments from week 28 onward

From week 28, appointments become more frequent — typically every two to four weeks, then weekly or fortnightly from week 36. They check blood pressure, urine, fundal height (a measurement that tracks growth), and fetal heartbeat. If you are rhesus negative, you will receive anti-D injections at weeks 28 and 34.

Fetal Movement: Monitoring, Patterns, and When to Call

Fetal movement monitoring is one of the most important tools you have in the second half of pregnancy — not because you should count obsessively, but because you know your baby's normal pattern better than anyone, and a change in that pattern is meaningful.

From around weeks 16–22, most people begin to feel their baby move. The sensations start very subtle — bubbles, flutters, a gentle tap — and can initially be confused with digestion. By week 28, you should have a settled sense of when your baby tends to be active and what their movements feel like. There is no specific number of movements per day that counts as "normal." What matters is what is normal for your baby.

Third Trimester Preparation

Weeks 28–40 are not just a waiting room — they are a distinct window of preparation that, if used well, makes the birth and early postpartum period significantly easier.

Hospital bag

Pack by week 36. For you: maternity notes, photo ID, your birth plan, nightwear, a nursing bra, toiletries, snacks, your phone charger, and a TENS machine if you plan to use one. For your baby: three vests, three sleepsuits, a hat, scratch mitts, a blanket, and nappies. For your birth partner: a change of clothes, snacks, a phone charger, and entertainment for the early latent phase — which can be a long wait. The car seat needs to be installed and ready before you leave for hospital.

Birth plan

A birth plan is not a binding contract — it is a way of ensuring your birth team understands your priorities before the moment arrives when explaining them becomes difficult. Cover your preferred pain relief, views on continuous monitoring, preferences around cord clamping and skin-to-skin, and any emotional or cultural considerations. The WiseMama guided birth plan tool walks you through every decision point step by step.

Recognising labour

Braxton Hicks are irregular and do not build in intensity or frequency over time. Latent labour brings irregular contractions that may be uncomfortable but do not follow a clear pattern — this phase can last hours or even days for first-time parents, and is completely normal. Established labour means regular contractions, typically three to four in ten minutes, lasting 45–60 seconds, increasing in intensity regardless of what you do. If your waters break before contractions start, call your maternity unit for guidance rather than waiting.