How many days is the first trimester

A Week-by-Week Pregnancy Calendar (for Parents)

en español: Calendario del embarazo semana a semana

Reviewed by: KidsHealth Medical Experts

Want to know what to expect during your pregnancy? You've come to the right place! Our illustrated pregnancy calendar is a detailed guide to all the changes taking place in your baby — and in you.

Each week of pregnancy includes a description of your baby's development, as well as an explanation of the changes taking place in your body. You'll also find important medical info that will help keep you and your baby healthy.

A Word About Due Dates and Trimesters

After you announce your pregnancy, the first question you'll probably be asked is "When are you due?" At your first prenatal visit, your health care provider will help you determine an expected delivery date (EDD). Your EDD is 40 weeks from the first day of your last menstrual period (LMP).

It's important to remember that your due date is only an estimate — most babies are born between 38 and 42 weeks from the first day of their mom's LMP and only a small percentage of women actually deliver on their due date.

Another common term you'll hear throughout your pregnancy is trimester. A pregnancy is divided into trimesters:

the first trimester is from week 1 to the end of week 12
the second trimester is from week 13 to the end of week 26
the third trimester is from week 27 to the end of the pregnancy

Getting Started

To get started, simply click below on the week of pregnancy you'd like to view. Many of the articles include links to other pregnancy and newborn articles with more information.

Check back every week of your pregnancy to see how your baby is developing and to find out what changes you can expect in your own body, too!

PREGNANCY CALENDAR: A week-by-week guide

PREGNANCY CALENDAR: A week-by-week guide

Trimester 1
Trimester 2
Trimester 3

Reviewed by: KidsHealth Medical Experts

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Everything you need to know about the first trimester (weeks 1 to 12)

Tommy's PregnancyHub

You’re pregnant: congratulations! The first weeks of your pregnancy are a vital time as your body gets busy building a baby. How exciting!

First trimester: key stages

The first trimester begins on the first day of your last period and lasts until the end of week 12. This means that by the time you know for sure you're pregnant, you might already be five or six weeks pregnant!

A lot happens during these first three months. The fertilised egg rapidly divides into layers of cells and implants in the wall of your womb where it carries on growing. These layers of cells become an embryo, which is what the baby is called at this stage.

During this trimester, your baby grows faster than at any other time. By six weeks, a heartbeat can usually be heard and by the end of week 12, your baby's bones, muscles and all the organs of the body have formed. At this point, your baby looks like a tiny human being and is now called a fetus. He or she will even be practising swallowing!

Try our Healthy Pregnancy Tool to find out everything you need to know about your pregnancy

When am I due?

Find out your due date using our due date calculator!

When will I see a midwife?

Your first midwife appointment (also known as antenatal appointment) is the 'booking' appointment. This usually happens between week 8 and 10 of your pregnancy. Find out how to register with a midwife and when your appointments will be here.

Keeping your baby safe

There are some things that you can do during pregnancy that have an effect on your baby. Find out about them by clicking the link below.

Find the complete list of pregnancy dos and don'ts (and reasons why) here

Not sure whether you are pregnant?

Find out about the symptoms that mean you may be pregnant here.

Your physical and mental health in pregnancy

We also have lots of useful tips for coping with everyday pregnancy niggles. It’s common for women to experience symptoms such as morning sickness, cramp and indigestion during the first trimester.

Don't forget that your mental health is just as important as your physical health. It's normal to feel some anxiety and stress but it shouldn't be ongoing. If what you’re feeling isn’t normal for you, talk to your GP or midwife about it. They are there to help.

Exercise, such as yoga, has been shown to reduce anxiety and is a great way to stay active during your pregnancy, too.

Read more about mental wellbeing in pregnancy

Track your baby's development

Sign up to a free pregnancy email from our midwives to track your baby's development and give you reminders of all you need to know through the 9 months of pregnancy. Click here to sign up.

Review dates

Reviewed: 28 June 2018

Next review: 28 June 2021

This content is currently being reviewed by our team. Updated information will be coming soon.

1st trimester of pregnancy: what happens to the fetus

1st trimester of pregnancy: what happens to the fetus - Private maternity hospital Ekaterininskaya Clinics

1st trimester: 1st-12th weeks

The gestational age is calculated from the first day of the last menstruation, since it is difficult to determine the exact day of conception. Since conception usually occurs in the middle of the menstrual cycle, you are not actually pregnant during the first two weeks, but this period is counted as the beginning of pregnancy.

As soon as the fertilization of the egg takes place around the 3rd week, the hormones begin to produce changes in your body little by little. As a result, you may experience some of the following symptoms:

Morning sickness. As a result of rising levels of hormones characteristic of pregnancy, up to 80% of women in the 1st trimester experience morning sickness with symptoms such as nausea and vomiting. The idea that such malaise is observed only in the morning is a common misconception. In fact, symptoms can appear at any time of the day or night. Up to 1 in 5 women experience morning sickness in the 2nd trimester of pregnancy and can sometimes persist throughout pregnancy.
If you experience morning sickness, avoid foods that make you sick, eat little and often, avoid fatty and spicy foods, drink more water. If you experience severe symptoms or symptoms that bother you, see your doctor.
Breast changes. The mammary glands will begin to increase in size, soreness may appear. The nipples will increase in size, become darker and more protruding.
Fatigue. High levels of the hormone progesterone can make you feel tired and sleepy. Rest as often as possible in a horizontal position with your legs up and eat as well as possible, which is not easy if you are experiencing morning sickness!
Increased emotionality. A higher level of emotionality, manifested as a result of an increase in hormone levels, is normal. Understanding and patience on the part of your partner and loved ones is very important here.
Food likes and dislikes. You may find yourself intolerant of one food and addicted to another. This is usually not a problem, unless you feel like eating weird foods like chalk. If you are concerned about the situation, contact your doctor.
Frequent urination. As your fluid levels increase and your uterus puts pressure on your bladder, you will become more likely to visit the toilet. Go to the toilet as soon as you feel the need - this minimizes the pressure on the bladder.
Feeling of dizziness. Sometimes you may feel a little dizzy (this is due to hormonal changes). Try not to stay on your feet for a long time and slowly rise from a sitting or lying position. If you experience severe dizziness, contact your doctor immediately.
Heartburn and constipation. Your digestive system will slow down to give you more time to digest your food. This can lead to heartburn and constipation. To help manage heartburn, try to eat small meals at regular intervals and avoid fried or spicy foods and carbonated drinks. Constipation is helped by eating a diet rich in fiber, maintaining physical activity and drinking plenty of water.

1st trimester milestones

Approximately 7 days after fertilization, the embryo implants in the uterine wall. The placenta, umbilical cord and amniotic sac will begin to form to provide nourishment and protection to the embryo.
By the end of the first 12 weeks of pregnancy, the uterus is palpable through the wall of the abdomen, the abdomen will begin to grow.

Child development in the 1st trimester of pregnancy

By the end of the 1st trimester:

All the main organs of the baby are formed, the circulatory system works.
The development of the sexual organs has begun.
Fingers are formed on the hands and feet, nails have appeared.
Facial features have formed.
The length of the baby's body is about 6 cm from the head to the lower part of the body, he is already recognizable. The baby moves in the amniotic sac, but you don't feel it move yet.

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1st trimester of pregnancy: everything you need to know | Mamovedia

The average gestation period is 40 weeks, counted from the date of the last menstrual period and measured in trimesters, months and weeks

The first trimester of covers the period from the 1st to the 12th week of pregnancy, which is approximately three months of the solar calendar. The second trimester starts at 13 weeks and ends at 27 weeks of pregnancy.
Finally, the third trimester covers the period from 28 weeks to the due date.

The first trimester of pregnancy is the most important for the development of your future baby.
During this period, the embryo (as the fetus of the first 8 weeks of life is defined) develops until it weighs from 14 to 28 grams, and growth, on average, from 7.5 to 10.5 centimeters.
Until the 20th week, the length of the embryo (and then the fetus) is usually measured from the head to the end of the spine. After that, its length is measured from head to toe.
The growth of the fetus in length will occur during the third, fourth and fifth months, and the increase in its weight will fall on the last two months of pregnancy.

What are the most common symptoms of pregnancy in the first trimester?

Usually the first symptoms accompanying pregnancy are nausea, vomiting, frequent urination, fatigue, breast tenderness . Many women begin to experience these symptoms even before a missed period or a positive pregnancy test result.

As your pregnancy progresses, you may begin to experience other symptoms such as mood swings, headaches, cramps, constipation, indigestion, bloating, food cravings or aversion, and an incredibly strong sense of smell: the latter often makes nausea worse.

Most of these symptoms, including mood swings and emotional outbursts, are believed to be caused by elevated levels of estrogen and progesterone.
If during this period you feel severe pain in the lower back, you have bleeding, severe nausea, it is recommended to consult a gynecologist, as these may be symptoms of a miscarriage.

First trimester weight gain

Fetus. The weight gain of the fetus in the first trimester is negligible: at the end of the first trimester, it is actually the size of a peach.
Expectant mother. Although the growth rate of the fetus is very subjective, the weight gain of the expectant mother by the end of the first three months should be about 1-2 kg.

During the first three months of motherhood, you can follow your regular diet and you don't have to eat for two!

Examinations and screenings during this period

As soon as you know you are pregnant, schedule your first appointment with your OB/GYN. The first examination is usually never done before the 8th week of pregnancy unless there is a risk of complications such as a history of abortion or a family history of hereditary genetic diseases. This visit is required for:

check for any abnormalities in the growing embryo;

Testing for HIV, syphilis, rubella, hepatitis B, as well as asymptomatic bacteriuria, chlamydia, toxoplasmosis is generally recommended for all women.
Ultrasonography as part of prenatal screening for genetic chromosomal risks should be performed between weeks 9 and 12 , along with a biochemical blood test for beta-hCG, PAPP-A and PIGF (optional) with a geneticist's conclusion. The woman must be informed of the abnormalities that may be found in order to have the choice of whether to continue the pregnancy or not.

What does the baby look like in the 1st trimester?

At the end of the 1st month the embryo reaches the size from 2 to 5 millimeters . The heart and stomach are being formed in him, the sensory apparatus and the structure from which the nervous system will originate begin to develop. In addition, cavities for the eyes are formed and the very first sketches of future upper limbs appear.

By the end of the second month of embryonic development, the contours of the head and face begin to be drawn; nostrils, mouth, bronchi and lungs begin to form; brain grows; the very first sketches of the lower extremities appear; the upper limbs lengthen, acquiring the shape of a scoop. At this stage, the retina also begins to develop. At the end of the 2nd month, the embryo reaches a size of 2.3 centimeters and a weight of 15 grams . The heart of the embryo makes 110 beats per minute.

By the end of the third month, the elbows begin to bend, the eyelids and outer ear are defined, the corpus callosum appears in the brain between the two hemispheres, the formation of bones, nerves, muscles and great vessels continues. The growth of the body is observed.
Formed liver produces red blood cells and bile fluid; sketches of future external genital organs (penis in men; clitoris and labia majora in women) begin to develop, which is why it is possible to predict the future sex of the child at an early stage. Nails appear on the fingers; the intestine passes into the abdominal cavity; teeth are laid; the pancreas begins to produce insulin.
At the end of the 3rd month, the fetus measures 6.5 centimeters and weighs about 73 grams .