From the very first day of your Last Menstrual Period (LMP), the clock starts on one of life's most remarkable journeys. Although it feels like a nine-month countdown, clinical obstetrics tracks a full 40 weeks, divided into three biological trimesters. Each stage brings its own fetal milestones, body changes and care priorities. This guide walks you through all of it — week by week.
Medical note: This is an educational wellbeing guide, not a substitute for personalised care. Always follow the advice of your own licensed obstetrician or midwife. The milestones below broadly align with ACOG and WHO antenatal guidance.
The First Trimester (Weeks 1–13): Building the Blueprint
The first trimester is an invisible construction site. You may not look pregnant yet, but your body is working at full capacity to build your baby's earliest organ systems.
Weeks 1 & 2 · Microscopic cluster of cells: You aren't technically pregnant yet. Your body clears the uterine lining and a surge of Follicle-Stimulating Hormone (FSH) releases a mature egg around day 14. Fertilisation in the fallopian tube creates a single-celled zygote.
Week 3 · Pinhead: The blastocyst burrows into your uterine lining (implantation), which can cause light, normal spotting. Your body begins producing hCG, prompting progesterone to preserve the pregnancy.
Week 4 · Poppy seed (~1 mm): hCG roughly doubles every 48 hours, making a home test highly accurate. The cluster splits — one half becomes your baby, the other the early placenta.
Week 5 · Sesame seed (~2 mm): Three cellular layers form. The outer layer folds inward to create the neural tube, the future brain and spinal cord. Heavy fatigue and breast tenderness often appear.
Week 6 · Sweet pea (~5 mm): A primitive tubular heart begins beating and can often be seen on a transvaginal ultrasound. Progesterone slows digestion, leading to early morning sickness and bloating.
Week 7 · Blueberry (~10 mm): The brain grows at a staggering rate, adding thousands of nerve cells a minute. Early nostrils and eyes begin positioning on the face.
Week 8 · Raspberry (~16 mm): Webbed fingers and toes emerge from the limb buds. The respiratory system branches into bronchial tubes. Your uterus, now lemon-sized, presses on your bladder.
Week 9 · Green olive (~23 mm): The embryonic phase ends — your baby is officially a fetus. The heart divides into four chambers. Mood swings may peak as hormones fluctuate.
Week 10 · Prune (~31 mm): Tiny wrists and elbows can bend, and tooth buds form under the gums. Rising blood volume can make veins more visible.
Week 11 · Lime (~40 mm): The fetus stretches and moves in the amniotic fluid — still too light to feel. The kidneys begin filtering and releasing early urine.
Week 12 · Plum (~54 mm): The placenta takes full control of hormone production and nutrient transfer. This is the turning point where intense morning sickness often begins to clear.
Week 13 · Meyer lemon (~74 mm): Intestines move from the umbilical cord into the abdomen. Crossing this week brings a meaningful drop in the risk of natural pregnancy loss.
First trimester action checklist
- Confirm your dating ultrasound with your OB-GYN to verify your due date.
- Take a quality prenatal vitamin providing around 400–600 mcg of folate/folic acid.
- Stay well hydrated to support your rapidly expanding blood volume.
- Discuss Non-Invasive Prenatal Testing (NIPT) and early genetic screening with your provider.
Do’s and don’ts
- Do choose thoroughly pasteurised dairy, juices and cheeses to lower listeriosis risk.
- Do avoid overheating — skip hot tubs and saunas, and keep your core temperature down.
- Don’t eat undercooked seafood, raw eggs or unpasteurised soft cheeses.
- Don’t take over-the-counter NSAIDs such as ibuprofen without your doctor’s approval.
Myth vs fact: The idea that you must immediately "eat for two" is a myth. In the first trimester your body needs essentially no extra daily calories — focus on nutrient density and hydration rather than larger portions.
The Second Trimester (Weeks 14–27): The Glow & The Growth
Welcome to the "honeymoon phase". Energy returns, appetite awakens, and your baby starts to make their presence known.
Week 14 · Nectarine (~85 mm): Your baby can squint, frown and grimace. The uterus rises out of the pelvis, easing pressure on your bladder.
Week 15 · Apple (~10 cm): A fine downy hair called lanugo covers the skin, and cartilage hardens into bone. Round-ligament pain on the sides of the lower belly is a normal sign of a stretching womb.
Week 16 · Avocado (~11.6 cm): The ears are fully formed — your baby can now hear your muffled heartbeat and voice, and may sense bright light through your abdomen.
Week 17 · Turnip (~13 cm): Brown fat deposits form under the skin, important for newborn warmth. Your appetite ramps up — prioritise lean protein and calcium-rich foods.
Week 18 · Artichoke (~14.2 cm): A myelin sheath wraps the nerves to speed up signalling. You may feel the first light, bubbly flutters — quickening, your baby’s first felt movements.
Week 19 · Heirloom tomato (~15.3 cm): A creamy barrier called vernix caseosa shields the skin inside the fluid. Estrogen may bring mild nasal congestion or minor nosebleeds.
Week 20 · Banana (~25 cm): The halfway point, marked by the detailed anatomy scan that evaluates the heart, brain, spine and limbs. Your uterus now sits level with your belly button.
Week 21 · Carrot (~26.7 cm): Your baby swallows amniotic fluid, training the digestive tract and forming meconium — the first dark stool passed after birth.
Week 22 · Spaghetti squash (~27.8 cm): The sense of touch is working — your baby explores their face and grips the cord. Your body makes red blood cells aggressively, so keep iron up to prevent gestational anaemia.
Week 23 · Large mango (~28.9 cm): The lungs start producing surfactant, which keeps the air sacs from sticking during practice breathing. REM sleep patterns begin.
Week 24 · Ear of corn (~30 cm): A major milestone — clinical viability. With intensive neonatal care a baby born now has a realistic chance of survival. You may feel rhythmic hiccups.
Week 25 · Rutabaga (~34.6 cm): Tiny capillaries give the skin a healthy pink hue, and the inner-ear balance structures mature.
Week 26 · Scallion bunch (~35.6 cm): Fused eyelids unseal — your baby can open their eyes and blink, and brain waves respond to outside sounds.
Week 27 · Head of lettuce (~36.6 cm): The trimester closes as the lungs keep maturing. Begin transitioning to side-sleeping to protect circulation.
Expert tip — the inferior vena cava rule: From around this point, avoid sleeping flat on your back. The weight of the uterus can compress the inferior vena cava, a major vein, reducing blood and oxygen flow. Sleep on your side — ideally the left — with a supportive pillow between your knees.
The Third Trimester (Weeks 28–40+): The Home Stretch & Delivery
The final stretch is about rapid weight gain, advanced brain development and preparing your body for labour.
Week 28 · Eggplant (~37.6 cm, ~1.1 kg): Sleep-wake cycles are distinct — a good time to begin tracking kick counts. In a restful hour you should note at least 10 clear movements within two hours.
Week 29 · Butternut squash (~38.6 cm, ~1.2 kg): The brain takes over breathing and temperature control. Bones pull calcium to harden, while the skull plates stay soft for delivery.
Week 30 · Large cabbage (~39.9 cm, ~1.4 kg): The brain surface folds into grooves, forming complex pathways. Painless, irregular Braxton Hicks contractions are your body practising for labour.
Week 31 · Coconut (~41.1 cm, ~1.5 kg): Billions of synaptic connections process sensory input. As the uterus pushes on your diaphragm, you may feel short of breath.
Week 32 · Jicama (~42.4 cm, ~1.7 kg): Fat fills out beneath the skin. Your provider will likely move to fortnightly visits to monitor blood pressure and swelling.
Week 33 · Pineapple (~43.7 cm, ~1.9 kg): Protective antibodies pass through the cord, giving your newborn temporary immunity for the first months of life.
Week 34 · Cantaloupe (~45 cm, ~2.1 kg): The nervous system is well advanced. Amniotic fluid begins to reduce as the baby fills the space, turning kicks into firm rolls.
Week 35 · Honeydew melon (~46.2 cm, ~2.4 kg): Most babies settle head-down (cephalic). If breech, your doctor may discuss an External Cephalic Version (ECV).
Week 36 · Romaine lettuce (~47.4 cm, ~2.6 kg): A routine Group B Streptococcus (GBS) swab is taken. The baby may drop into the pelvis — "lightening" — easing your breathing but adding pelvic pressure.
Week 37 · Winter melon (~48.6 cm, ~2.9 kg): Officially early term — the organs are ready to work outside the womb. A loss of thick discharge may be the mucus plug releasing.
Week 38 · Pumpkin (~49.8 cm, ~3.1 kg): Sucking and swallowing reflexes coordinate, ready for feeding. Keep your feet elevated to ease swelling.
Week 39 · Watermelon (~50.7 cm, ~3.3 kg): Full term. Watch for signs of active labour: regular contractions that strengthen over time, or your water breaking.
Week 40+ · Jackfruit (~51.2 cm, ~3.5 kg): Your due date arrives — though only about 5% of babies are born on it. Going a little past 40 weeks is common and safe, with your team monitoring you closely.
Third trimester readiness checklist
- Pack your hospital bag: ID, birth preferences, comfortable clothing and newborn essentials.
- Install your infant car seat and have it checked by a certified technician.
- Choose a pediatrician and finalise care arrangements for your baby’s first checkup.
- Wash newborn clothes and sheets with a gentle, fragrance-free detergent.
Evidence-based references
- American College of Obstetricians and Gynecologists (ACOG). Nutrition During Pregnancy: Clinical Guidelines and Folic Acid Requirements.
- Maternal-Fetal Medicine reviews on fetal morphogenesis and cardiovascular development.
- World Health Organization (WHO). Antenatal Care Recommendations for a Positive Pregnancy Experience.
This guide is for education and reassurance only and does not replace personalised medical care. For any symptom that worries you — bleeding, severe pain, reduced movement, or signs of labour — contact your healthcare provider promptly.
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