How are weeks of pregnancy counted?

The stage is counted in obstetric weeks — from the first day of the last period, not from conception (so the obstetric stage is about 2 weeks more than the 'embryonic' one). Pregnancy lasts about 40 weeks and is divided into three trimesters: 1st (1–13), 2nd (14–27) and 3rd (28–40 weeks).

Which tests and screenings are done by week?

Key points: the first screening at 11–13 weeks (ultrasound + blood), the second screening and anatomy ultrasound at 18–21, the gestational diabetes test at 24–28, the third ultrasound and CTG at 30–34 weeks. Plus a regular blood count and urine test — the full list is in pregnancy tests.

When are the first fetal movements felt?

Most often the first fetal movements are felt at 18–22 weeks, sometimes earlier in second pregnancies. At first they are rare and faint, becoming regular by the third trimester. A sharp decrease or absence of movements in late pregnancy is a reason to see a doctor urgently.

What happens in each trimester?

In the first trimester the baby's organs form and the mother may have toxicosis. The second is usually calm: the bump grows and movements appear. In the third the baby grows actively and prepares for birth, with more frequent visits and exams (blood pressure, swelling, CTG). Details are in the topic articles.

Can I decode tests at any stage online?

Yes, to understand the form. Upload the result (PDF or photo) to the lab results interpretation service — the AI will explain the markers for the week of pregnancy and 'pregnancy' norms in plain language. This helps you understand the result at your stage, but care decisions are made by the doctor.

Pregnancy Week by Week: What Happens and Which Tests

PregnancyJune 28, 2026

Reviewed by the LabReadAI medical team

Pregnancy Week by Week: What Happens and Which Tests

Pregnancy is conveniently tracked week by week: each stage has its own changes for the baby and mother and its own set of exams. This is an overview guide by week and trimester — what happens and which tests are done, with links to detailed articles on each topic.

Pregnancy by Trimester and Week

Pregnancy is counted in obstetric weeks (from the first day of the last period), about 40 weeks in total. They are divided into three trimesters:

Trimester	Weeks
1st trimester	1–13
2nd trimester	14–27
3rd trimester	28–40

First Trimester (1–13 Weeks)

The baby's organs form. The mother has the first signs of pregnancy, often toxicosis. She registers for care, takes the basic pregnancy tests and has the first screening (ultrasound + blood at 11–13 weeks).

Second Trimester (14–27 Weeks)

Usually the calmest period: toxicosis eases, the bump shows, the first fetal movements are felt. The second screening and a detailed ultrasound are done, a gestational diabetes test is taken, haemoglobin is monitored (anaemia).

Third Trimester (28–40 Weeks)

The baby grows actively and prepares for birth. Visits become more frequent, with monitoring of blood pressure and swelling, CTG and Doppler ultrasound. Closer to term, signs of labour appear.

Key Exams, Tests and Screenings by Week

11–13 weeks — first screening (ultrasound + blood);
18–21 weeks — second screening, anatomy ultrasound;
24–28 weeks — gestational diabetes test (OGTT);
30–34 weeks — third ultrasound, Doppler, CTG;
regularly — complete blood count and urine test, blood pressure and weight control.

When to See a Doctor

Out of schedule — with alarming symptoms: bloody discharge, severe abdominal pain, high blood pressure, facial swelling, no fetal movements. The exact schedule of visits and tests is set by the doctor.

To understand any tests at your stage in plain language, upload the form (PDF or photo) to the lab results interpretation service: the AI will explain the markers for the week of pregnancy. This helps you understand the result but does not replace a doctor.

This article is informational and an overview. Pregnancy care is the doctor's job.

Frequently asked questions

The stage is counted in obstetric weeks — from the first day of the last period, not from conception (so the obstetric stage is about 2 weeks more than the 'embryonic' one). Pregnancy lasts about 40 weeks and is divided into three trimesters: 1st (1–13), 2nd (14–27) and 3rd (28–40 weeks).
Key points: the first screening at 11–13 weeks (ultrasound + blood), the second screening and anatomy ultrasound at 18–21, the gestational diabetes test at 24–28, the third ultrasound and CTG at 30–34 weeks. Plus a regular blood count and urine test — the full list is in pregnancy tests.
Most often the first fetal movements are felt at 18–22 weeks, sometimes earlier in second pregnancies. At first they are rare and faint, becoming regular by the third trimester. A sharp decrease or absence of movements in late pregnancy is a reason to see a doctor urgently.
In the first trimester the baby's organs form and the mother may have toxicosis. The second is usually calm: the bump grows and movements appear. In the third the baby grows actively and prepares for birth, with more frequent visits and exams (blood pressure, swelling, CTG). Details are in the topic articles.
Yes, to understand the form. Upload the result (PDF or photo) to the lab results interpretation service — the AI will explain the markers for the week of pregnancy and 'pregnancy' norms in plain language. This helps you understand the result at your stage, but care decisions are made by the doctor.

#Pregnancy Tests #Pregnancy Screening #Ultrasound in Pregnancy #Fetal Movements

For informational purposes only

This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Please consult a healthcare professional for medical guidance.

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