TimeDateStack WEEK 3
First Trimester • less than 1 month

3 Weeks Pregnant: Baby Size, Symptoms & Due Date Milestones

Comprehensive gestational timeline analysis, fetal growth metrics, anatomical development, and personalized due date milestones for week 3.

Gestational Classification
At 3 weeks pregnant, you are in your First Trimester

Equivalent to less than 1 month • 21 calendar days of gestation completed

Overall Gestational Progress 7.5% of 40 Weeks (21 of 280 Days)
Days Pregnant
21 Days
Exact duration
Days Until Due Date
259 Days
37.0 weeks left
Trimester Stage
1st Trimester
Weeks 1 – 13
Fetal Size Category
Pinhead (Implantation)
0.15 mm

Baby Development at 3 Weeks Pregnant

Baby Size Comparison
Pinhead (Implantation)

Fruit / Vegetable Analogy

Estimated Length
0.15 mm

Crown to Rump (CRL)

Estimated Weight
< 1 mg

Fetal Weight Standard

At week 3, the fertilized single cell undergoes rapid cleavage, dividing into 2, 4, 8, and 16 cells as it travels through the Fallopian tube toward the uterus. By day 4 post-conception, it forms a dense spherical cluster called a morula.

Upon entering the uterine cavity around day 5 to 6, fluid accumulates inside the cluster to form a blastocyst. The outer ring of cells (trophoblast) will develop into the placenta, while the inner cell mass will form the embryo.

Personalized Due Date Recalculator

Input your last menstrual period (LMP) to verify your exact week, remaining days, and estimated delivery date.

Real-Time Engine
Recalculated Due Date
Select your LMP date
Days Remaining
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Current Gestation
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Disclaimer: Computational estimates are based on standard clinical algorithms (e.g., Naegele's rule) for educational and planning purposes only. They do not constitute formal medical evaluation, diagnosis, or clinical obstetrics advice.

Disclaimer: Computational estimates are based on standard clinical algorithms (e.g., Naegele's rule) for educational and planning purposes only. They do not constitute formal medical evaluation, diagnosis, or clinical obstetrics advice.

Maternal Symptoms & Clinical Guidance at Week 3

Common Physical Symptoms

  • Light pinkish or brownish spotting (implantation bleeding)
  • Mild lower abdominal twinges or gentle uterine tugging
  • Heightened emotional sensitivity or mood fluctuations
  • Very early breast tenderness

Clinical Action Items

  • Note any light implantation spotting in your tracking app
  • Avoid strenuous high-impact contact sports while implantation occurs
  • Continue avoiding hot tubs, saunas, and excessive heat exposure
  • Ensure adequate dietary zinc, folate, and iron

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Frequently Asked Questions About 3 Weeks Pregnant

Implantation bleeding occurs when the blastocyst burrows into the vascular lining of the endometrium, typically 6 to 12 days after conception (around week 3 to early week 4). It is usually light pink or brown, lasts from a few hours to two days, and is much lighter than a regular period.