8 min read
2026-03-01
The obstetric gestational age is counted from the first day of the last menstruation (LM). The average duration of pregnancy is 280 days (40 weeks).
**PDR = PM date minus 3 months + 7 days + 1 year**
Example: PM May 15, 2025 - PDR = February 22, 2026
| Trimester | Weeks | Key events |
|---|---|---|
| I | 1-13 | Organ formation, toxicosis |
| II | 14-27 | Active growth, first movements |
| III | 28-40 | Maturation of the lungs, preparation for childbirth |
| Week | Survey |
|---|---|
| 6-8 | First ultrasound, confirmation of pregnancy |
| 11-13 | First trimester screening (ultrasound + blood test) |
| 16-20 | Second trimester screening |
| 18-22 | Detailed ultrasound of fetal anatomy |
| 24-28 | Gestational Diabetes Test |
| 30-34 | Ultrasound of the third trimester, CTG |
| 36-40 | Weekly Observation |
All major organs and systems are formed. By week 12, the length of the fetus is about 6 cm, weight - 14 g.
A period of active growth. Mom begins to feel movements (18-22 weeks). By week 27, the fetal weight is about 1 kg.
The fetus is gaining weight and preparing for birth. Average birth weight is 3.0-3.5 kg.
Bloody discharge
Severe abdominal pain
No movement for more than 12 hours (after 28 weeks)
Sharp increase in blood pressure, swelling
See also: Ideal weight calculator, Water norm calculator, Calorie calculator