Week-by-Week Pregnancy Timeline (Weeks 1–42)

Medical disclaimer: Educational content only, not medical advice. Gestational dating, screening windows, and delivery timing must be individualized with your obstetric team. Evidence tags: (a) settled consensus, (b) emerging/contested, © traditional with limited study, (d) popular claims with little support — see Evidence Rating Key.

This page is the index by time. Protocol depth lives on the India-stage and research pages linked below. Clustered trimester chapters remain useful for narrative reading: First · Second · Third. Full visit calendar: ANC calendar.

How weeks are counted

Gestational age is usually counted from the first day of the last menstrual period (LMP) — not from conception (a).
Week N covers days N×7 through N×7+6 (for example, Week 19 = days 133–139 from LMP).
Weeks 1–2 are often before fertilization by this convention; ovulation/conception typically land around Week 2–3 in a textbook 28-day cycle (a).
An early dating/viability scan may move your due date; trust the clinician’s dating over an app alone (a).
Notation like 40+3 means 40 completed weeks + 3 days — relevant mainly for post-dates planning (see Weeks 40–42).
Day-of-cycle fertile-window detail belongs on Fertility, not here — pregnancy guidelines are week-level, not day-level (a).

Jump: T1 · Weeks 1–13 · T2 · Weeks 14–27 · T3 · Weeks 28–40+ · Post-dates

First trimester — Weeks 1–13 · India: Preconception & T1 · Research: First trimester

Week 1

Baby (a): By LMP dating, this is still the menstrual/pre-ovulatory phase — no embryo yet. You (a): Period may be ending; continue preconception habits if TTC. Clinical this week: Folic acid if planning/pregnant; HPLC/chronic-disease optimization ideally already started → Fertility · Preconception & T1 Watch for: None specific to pregnancy yet.

Week 2

Baby (a): Ovulation and possible fertilization near the end of this week (cycle-dependent). You (a): Fertile window; intercourse timing matters if TTC → Fertility Clinical this week: Still pre-implantation for most; pregnancy tests usually negative. Watch for: None pregnancy-specific.

Week 3

Baby (a): Fertilization → early cell division; travel toward the uterus. You (a): Usually no reliable pregnancy symptoms yet. Clinical this week: Avoid new teratogens (alcohol, smoking, unnecessary meds) if TTC/possible pregnancy → Toxicology Watch for: Severe one-sided pain + spotting later can signal ectopic — seek care (a) · Pregnancy loss

Week 4

Baby (a): Implantation often completes; hCG rises; neural plate begins forming. You (a): Missed period possible; breast tenderness, mild cramping, implantation spotting in some (a). Clinical this week: Home urine pregnancy test often positive; register ANC when confirmed → Preconception & T1 · ANC calendar Watch for: Heavy bleeding, severe unilateral pain, fainting → urgent care (a) · First trimester red flags

Week 5

Baby (a): Neural tube closing; early heart tube forming; embryo still tiny. You (a): Fatigue, nausea may begin; breast changes common (a). Clinical this week: Confirm pregnancy; continue folic acid; review meds with clinician → Nutrition · Toxicology Watch for: Inability to keep fluids down (hyperemesis pathway) → Special topics

Week 6

Baby (a): Heartbeat often detectable on transvaginal ultrasound ~this week; limb buds appear (a). You (a): Nausea/urination frequency often rising (a). Clinical this week: Dating/viability scan commonly offered in the 6–10 week window → First trimester screening · ANC Watch for: Ectopic red flags; heavy bleeding (a) · Pregnancy loss

Week 7

Baby (a): Rapid organogenesis; head large relative to body; arm/leg buds lengthen (a). You (a): Morning sickness peak window often weeks 4–9 (a). Clinical this week: Baseline labs if first ANC done early (CBC, blood group/Rh, infections, urine) → Preconception & T1 checklist Watch for: Dehydration, weight loss from vomiting (a).

Week 8

Baby (a): Major organ systems have begun; embryo ~2.5 cm / ~1 inch order of magnitude (a). You (a): Symptoms often prominent; mood swings common (a). Clinical this week: Viability/dating if not done; PMSMA high-risk categorization at registration → Preconception & T1 Watch for: Same T1 red flags (a).

Week 9

Baby (a): Transition toward fetal period approaching; fingers/toes separating (a). You (a): Nausea may still be strong; constipation common (a). Clinical this week: Td-1 timing often at first ANC registration (schedule per clinician) → Preconception & T1 · Toxicology Watch for: Persistent severe vomiting (a).

Week 10

Baby (a): Embryonic → early fetal period; organs continue refining (a). You (a): Uterus still largely pelvic; symptoms variable (a). Clinical this week: NIPT available from ~10 weeks where offered (a) → First trimester screening Watch for: Bleeding/pain (a).

Week 11

Baby (a): Rapid growth; facial features more defined (a). You (a): Energy may still be low (a). Clinical this week: First-trimester combined screening window opens (~11–14 weeks: NT + PAPP-A/β-hCG) where available (b) → First trimester · ANC Watch for: Same T1 red flags (a).

Week 12

Baby (a): Heartbeat often audible with Doppler in clinic; miscarriage risk falls substantially after heartbeat confirmed and this stage (a). You (a): Some notice nausea easing toward weeks 12–14 (a). Clinical this week: Combined screening / NT still in window; Rh status should be known for later Anti-D plan → Special topics — Rh Watch for: Heavy bleeding still warrants care (a).

Week 13

Baby (a): End of first trimester by many definitions; organs formed in outline, growth ahead (a). You (a): Transition toward “comfort window” for many (a). Clinical this week: Finish T1 labs/screening backlog; discuss low-dose aspirin if high preeclampsia risk (clinician-directed, often from ~12–16 weeks) (a) → ANC Watch for: Persistent hyperemesis (a).

Second trimester — Weeks 14–27 · India: Trimester 2 · Research: Second trimester

Week 14

Baby (a): Rapid growth; bones harden (skull stays flexible); lanugo begins (a). You (a): Energy often returns; uterus rising (a). Clinical this week: Start IFA + calcium supplementation per India schedule from week 14 (a) → Trimester 2 master schedule · Nutrition Watch for: Painless bright-red bleeding → evaluate placenta issues (a) · T2 red flags

Week 15

Baby (a): Continued growth; early movement present but often not felt yet (a). You (a): Round-ligament twinges may start (a) · Physical health Clinical this week: Ongoing ANC: BP, weight, symptom review (a) · ANC calendar Watch for: Fluid leak, regular painful contractions (preterm) (a).

Week 16

Baby (a): Movements more organized; multiparous parents may feel quickening soon (a). You (a): Comfort window often underway (a). Clinical this week: Monochorionic twins: TTTS surveillance commonly starts ~16 weeks with serial scans (a) → Special topics · Second trimester multiples Watch for: Preterm labour signs; severe headache (a).

Week 17

Baby (a): Fat stores beginning; skeleton continues ossifying (a). You (a): Appetite often up; nasal congestion/gum bleeding possible (a). Clinical this week: Plan TIFFA booking for 18–22 (to 24) weeks (a) → Trimester 2 Watch for: Itching without rash — consider ICP workup (b) → ICP patch

Week 18

Baby (a): Anatomy increasingly detailed on ultrasound; swallowing amniotic fluid (a). You (a): Quickening common around 16–20 weeks (earlier if subsequent pregnancy) (a). Clinical this week: TIFFA / Level II anomaly scan window opens (18–22, India often to 24) (a) → Trimester 2 · Second trimester screening Watch for: Bleeding, PPROM-like leak (a).

Week 19

Baby (a): Vernix begins forming; sensory systems maturing (a). You (a): Round-ligament pain common; linea nigra/melasma may appear (a). Clinical this week: Mid–anomaly-scan window; PCPNDT-compliant sex disclosure rules apply in India (a) → Trimester 2 Watch for: Same T2 red flags (a).

Week 20

Baby (a): Halfway by calendar for a 40-week pregnancy; skin developing; movements stronger (a). You (a): Fundal height roughly at umbilicus in many (clinician measures) (a). Clinical this week: Anatomy scan if not done; avoid prolonged flat-supine yoga after ~20 weeks (a) → Physical health Watch for: Short cervix findings if screened — specialist path (a) → Cervical insufficiency

Week 21

Baby (a): Bone marrow blood cell production ramps; digestive practice continues (a). You (a): Backache, Braxton–Hicks may appear later in T2 (a). Clinical this week: Complete anomaly scan follow-ups (a). Watch for: Regular painful contractions before 37 weeks (a).

Week 22

Baby (a): End of classic 18–22 anatomy window; eyelids still fused in many descriptions (a). You (a): Stretch marks/skin changes possible (a). Clinical this week: India anomaly scan accepted through ~24 weeks in many centres (a) → ANC Watch for: Painless bleeding; severe headache/vision changes (a).

Week 23

Baby (a): Rapid brain growth; hearing developing (a). You (a): Sleep position often side-lying more comfortable (a). Clinical this week: Continue IFA/calcium; anemia surveillance (a) → Trimester 2 Watch for: Reduced movement perception varies — report a clear change once movements are established (a).

Week 24

Baby (a): Surfactant production begins (critical for air breathing); viability threshold discussions are clinical and individual (a). You (a): Uterus higher; heartburn more common (a). Clinical this week: DIPSI GDM screen window 24–28 weeks (if early screen negative/as indicated) (a) → Trimester 2 · Second trimester Watch for: Preterm labour signs; glucose-related symptoms per clinician (a).

Week 25

Baby (a): Fat increasing; response to sound/light emerging (a). You (a): Braxton–Hicks possible (a). Clinical this week: Mid–GDM screening window; Rh-negative: plan ICT/Anti-D timing (a) → Trimester 2 §5 Watch for: Fluid leak, bleeding (a).

Week 26

Baby (a): Eyes beginning to open in many timelines; lungs still immature (a). You (a): Leg cramps, backache common (a) · Physical health Clinical this week: Complete GDM testing if due; mental-health check-in useful → Mental health Watch for: Preeclampsia-type symptoms (more common later, still act early) (a).

Week 27

Baby (a): Sleep–wake cycles; continued lung/brain maturation (a). You (a): End of second trimester for many definitions (a). Clinical this week: Finish 24–28 week labs; prepare for third-trimester visit cadence → ANC · Trimester 3 Watch for: Same T2 red flags (a).

Third trimester — Weeks 28–40+ · India: Trimester 3 · Research: Third trimester · Birth: Labor & delivery

Week 28

Baby (a): Rapid brain growth; body fat rising; eyes detect light (a). You (a): Shortness of breath, pelvic pressure may increase (a). Clinical this week: Anti-D 300 mcg for Rh-negative unsensitized mothers where indicated; start daily movement pattern awareness (a) → Trimester 2 Anti-D · Trimester 3 movements · Rh patch Watch for: Decreased fetal movements — seek prompt evaluation (a) · T3 red flags

Week 29

Baby (a): Muscles/lungs maturing; hiccups common (a). You (a): Sleep disruption, heartburn, hemorrhoids possible (a). Clinical this week: Growth scan often offered 28–32 weeks in Indian practice (a) → Trimester 3 · ANC Watch for: Preeclampsia signs; PPROM (a).

Week 30

Baby (a): Bone marrow active; weight gain accelerates (a). You (a): Braxton–Hicks more noticeable (a). Clinical this week: Repeat Hb/CBC often in 28–32 week window (a) → Trimester 3 Watch for: Regular contractions, bleeding, reduced movements (a).

Week 31

Baby (a): Further fat deposition; immune transfers from mother ongoing (a). You (a): Pelvic pressure; varicose veins possible (a). Clinical this week: Continue BP/urine protein each visit (a). Watch for: Epigastric/RUQ pain, severe headache, visual changes (a).

Week 32

Baby (a): Most systems maturing; movements remain a key well-being signal (a). You (a): Practice labour positions/breathing if useful → Physical health · Labor & delivery Clinical this week: Complete 28–32 growth/Hb work if pending (a). Watch for: Preterm labour before 37 weeks (a).

Week 33

Baby (a): Bones hardening further; skull remains flexible for birth (a). You (a): Frequent urination returns as baby drops later (a). Clinical this week: Birth preparedness discussion starting → Trimester 3 · Practical planning Watch for: Abruption-type sudden pain ± bleeding (a).

Week 34

Baby (a): Lungs more mature than earlier preterm weeks; still benefit from more time in uncomplicated pregnancies (a). You (a): Hospital bag / transport plan (108/102) (a) → Trimester 3 Clinical this week: Birth preparedness 34–36 weeks common target (a) · Practical planning Watch for: Reduced movements; PPROM (a).

Week 35

Baby (a): Rapid weight gain; positioning (cephalic vs breech) assessed clinically/sonographically (a). You (a): Pelvic pressure if head engaging (a). Clinical this week: GBS swab 35–37 weeks in some hospitals — not universal in India (a) → Trimester 3 GBS Watch for: Labour signs before 37 weeks (a).

Week 36

Baby (a): Vernix decreases; many organ systems near term readiness (a). You (a): Braxton–Hicks vs true labour education → Labor & delivery Clinical this week: Common Indian ~36-week growth/placental position scan (a) → Third trimester screening Watch for: Painless late bleeding (previa pathway) (a).

Week 37

Baby (a): Early term begins (37+0); lungs typically adequate for birth in uncomplicated pregnancies (a). You (a): Know labour onset signs, when to go in (a) → Labor & delivery · Trimester 3 Clinical this week: Visit frequency often increases; finalize birthplace/partner plan (a) · Practical planning Watch for: Reduced movements — still urgent (a).

Week 38

Baby (a): Continuing fat gain; meconium present in gut (a). You (a): Nested insomnia common; rest when possible (a). Clinical this week: Twin delivery timing often earlier (dichorionic ~37–38; monochorionic earlier) — individualize (a) → Third trimester multiples Watch for: Labour, ROM, bleeding, preeclampsia signs (a).

Week 39

Baby (a): Full term window underway; waiting for spontaneous labour is common if uncomplicated (a). You (a): Mucus plug/bloody show may appear — not always labour (a) → Labor & delivery Clinical this week: Confirm induction criteria discussion if needed later (a). Watch for: Same T3 red flags (a).

Week 40

Baby (a): Due date (EDD) by dates/scan — only ~5% deliver on the exact day (a). You (a): Expect surveillance plan if pregnancy continues (a). Clinical this week: Post-dates counselling begins; membrane sweep/induction pathways are clinician-specific (a) → Labor & delivery Watch for: Reduced movements; ROM; heavy bleeding (a).

Week 41

Baby (a): Post-dates (41+0) — still often healthy; surveillance intensifies (a). You (a): NST/AFI or equivalent monitoring per facility protocol (a). Clinical this week: Many guidelines offer induction by 41+0–42+0; decide with your team (a) → Labor & delivery · Trimester 3 Watch for: Any change in movement pattern — do not wait for the next appointment (a).

Week 42

Baby (a): 42+0 is late term / post-term territory — induction usually recommended to reduce stillbirth risk (a). You (a): Delivery planning should already be active with your obstetric team (a). Clinical this week: Induction / continuous monitoring pathways → Labor & delivery · Practical planning Watch for: Same urgent labour/fetal-movement red flags (a).

After birth — next pages

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