Pregnancy Calculator — Week 3: Baby Size, Symptoms & Due Date
You are in week 3 of a standard singleton pregnancy. Below is a complete evidence-based snapshot — baby's growth, your body, nutrition, exercise, red flags and a doctor visit checklist for this exact week.
Pregnancy Calculator
Enter the first day of your last menstrual period (LMP). EDD = LMP + 280 days.
Baby at week 3
This week: The fertilised egg (zygote) travels down the fallopian tube dividing rapidly, becoming a blastocyst by day 5–6.
Mother's body — what changes
In week 3 you may notice: Zero visible symptoms. Blastocyst is preparing to implant into the uterine wall this week.
Nutrition & supplements
Focus on folic acid 400–600 mcg/day (neural tube), iodine 150 mcg, and small frequent meals to counter nausea. No extra calories yet — normal maintenance intake is adequate.
Safe exercise
150 minutes/week of moderate activity — brisk walking, stationary cycling, prenatal yoga. Stop any exercise that leaves you unable to hold a conversation.
Doctor visit checklist — week 3
- ✓Avoid alcohol, smoking, X-rays and category X medications
- ✓Blood pressure + weight + urine dipstick at every visit
- ✓Fetal heart tones from week 10–12 (Doppler)
Warning signs — call your provider immediately
- ⚠Heavy bleeding (soaking a pad in an hour)
- ⚠Severe abdominal pain that does not ease
- ⚠Fever above 38°C / 100.4°F
- ⚠Sudden loss of pregnancy symptoms + spotting
- ⚠Severe one-sided pain (ectopic pregnancy signal)
Week 3 — Frequently asked questions
How accurate is the Pregnancy Calculator at week 3?
The calculator uses standard gestational-age arithmetic (LMP + 280 days for standard; egg retrieval + 266 days for IVF day-5). Ultrasound crown-rump length between weeks 8–13 is more accurate (±5 days) than LMP — adjust EDD accordingly if the scan differs by more than 7 days.
What size is my baby at week 3?
Approximately the size of a pinhead — length 0.01 cm and weight 0 g. These are median values from ACOG, NHS UK and Mayo Clinic references.
Which symptoms are normal in week 3?
Zero visible symptoms. Blastocyst is preparing to implant into the uterine wall this week. Every pregnancy is different — call your provider if anything on the warning-signs list appears.
Should I have an ultrasound at week 3?
Avoid alcohol, smoking, X-rays and category X medications. Routine scan windows are: dating (10–13w), anatomy (18–22w), growth (28–32w).
How much weight should I gain by week 3?
Approximately 0.4 kg cumulative if you started at a normal BMI (IOM guideline). Underweight mothers gain more; overweight mothers less.
What is my EDD if today is week 3?
Your estimated due date is 37 weeks from today. Calculator adds (280 − 7 × 3) days to today's date.
Can I travel during week 3?
Yes, but morning sickness may make flying uncomfortable. Airlines allow travel until week 36 for singleton, week 32 for twins.
Content aligned with ACOG, NHS UK and Mayo Clinic. Reviewed by Dr. Maria Rehman, MD (OB/GYN). This page is educational and does not replace personal medical advice — call your obstetrician for any concern.