From the moment ofconceptionto the time of delivery, your growing baby goes through several stages of development. The first third of your pregnancy is called the first trimester. It’s made up of weeks 1 through 12 or 13 of pregnancy. Here is a summary of how your baby develops during the first trimester.
Path to improved health
Pregnancy begins when aman’s spermfertilizes a woman’s egg. Since you don’t always know whenfertilizationoccurred, doctors calculate pregnancy based on the first day of your last menstrual period (LMP). Your doctor will count forward 40 weeks from your LMP to estimate the due date. Most births occur between weeks 38 and 42. If you have anultrasoundearly in your pregnancy, your doctor may measure the baby to determine your due date instead.
After conception, your baby begins a period of dramatic change known as theembryonic stage. This stage runs from the 5th through the 10th week of pregnancy. During this stage, the baby is called an embryo.
There are numerous changes that occur during the embryonic stage. First, the cells of the embryo (called embryonic stem cells) multiply and develop. They become the hundreds of different types of cells needed to make a whole human body. Your baby’s major organs and body parts begin to take shape.
Theplacentaforms during the embryonic stage. The placenta takes nutrients,oxygen,and water from yourbloodand passes these along to your baby through the umbilical cord. It also removes the baby’s wastes. The placenta will filter out most of the harmful substances that may be present in your body.
The amniotic sac forms during this stage as well. It is filled with amniotic fluid, which surrounds and protects your baby in the uterus.
Below are some of the highlights that occur during the embryonic stage.
- Nervous system.This is one of the first things to develop. It includes the formation of your baby’s brain, spinal cord, and nerves.
- Heart.An S-shaped tube forms on the front of the embryo. This will become your baby’s heart. At first theheartdoesn’t beat, but soon it starts beating and pumping an early form of blood.
- Face.Your baby’s facial features begin to take shape. The eyes and ears form on the sides of the head and are linked to the brain. The eyes move forward on the face, and eyelids form to protect the developing eyes. Pieces oftissuegrow and join together to create the forehead, nose, cheeks, lips, and jaw. The nasal passages, mouth, and tooth buds form the baby’s first teeth. Atonguewith taste buds also forms.
- Arms and legs.At first, your baby’s arms and legs begin as little buds that sprout from the embryo’s sides. As they grow, the arms look like paddles and the legs look like flippers. A ridge appears on the end of each one. They eventually become your baby’s fingers and toes.
- Sexual organs.Cells form to become your baby’s eggs or sperm. Your baby’s vagin* or penis is visible at the end of the embryonic period. However, it’s still too soon to tell on an ultrasound if your baby is a girl or boy.
- Muscles and movement.Muscles develop and the embryo begins to move. At first it’s only twitching and reacting to touch. Once the nerves and muscles start working together, your baby can start moving on purpose.
By the end of the embryonic stage at week 10 of your pregnancy, your baby will be about 1 inch long. That’s still too small for you to feel your baby’s movements. You’ll probably feel them starting in the middle of the second trimester.
After the embryonic stage, thefetalstage begins and your baby is called a fetus. This stage runs from the 11th week until birth. Your baby will grow longer and gain weight quicker. His or her organs and body parts will continue to develop. Fingernails and toenails begin to form and the kidneys start working. By the end of the first trimester, your baby has tripled in length to about 3 inches long.
Things to consider
As your baby develops in the womb, your body goes through a lot of changes as well. Make an appointment with your doctor if you think or know you’re pregnant. He or she will be able to confirm your pregnancy. Your doctor will also talk with you about your baby’s development and prenatal care. So much important development happens during the first trimester. It is important to not take any medicines without first asking the advice of your doctor.
Questions for your doctor
- Am I pregnant?
- How far along am I in my pregnancy?
- What weeks do you consider to be the first trimester?
- What lifestyle changes should I make to support my baby’s development?
- Are there any risks to the baby or me that I should be aware of?
Resources
American Academy of Family Physicians: Changes in Your Body During Pregnancy: First Trimester
March of Dimes: Pregnancy Week by Week
National Institutes of Health, MedlinePlus: Fetal Development
Copyright © American Academy of Family Physicians
This information provides a general overview and may not apply to everyone. Talk to your family doctor to find out if this information applies to you and to get more information on this subject.
FAQs
Your baby will grow longer and gain weight quicker. His or her organs and body parts will continue to develop. Fingernails and toenails begin to form and the kidneys start working. By the end of the first trimester, your baby has tripled in length to about 3 inches long.
What does the baby develop in the first trimester? ›
The neural tube (which becomes the brain and spinal cord), the digestive system, and the heart and circulatory system begin to form. The beginnings of the eyes and ears are developing. Tiny limb buds appear, which will develop into arms and legs. The heart is beating.
What is the 1st trimester of pregnancy? ›
Although you are pregnant from the moment of conception — when a sperm fertilises your ovum (egg) —the first trimester of pregnancy is counted from the first day of your last period through to week 12. This is because when you conceive naturally, you usually won't know the date of conception.
What should be avoided in the first trimester? ›
These things should be avoided during the first trimester:
- strenuous exercise or strength training that could cause an injury to your stomach.
- alcohol.
- caffeine (no more than one cup of coffee or tea per day)
- smoking.
- illegal drugs.
- raw fish or smoked seafood (no sushi)
Sore and enlarged breasts, increased vagin*l discharge, morning sickness, and exhaustion may not be the most pleasant pregnancy symptoms to experience, but they are each signs of a healthy pregnancy. Talk to your doctor for tips and advice on how to manage symptoms that are particularly difficult.
How does the brain develop in the first trimester? ›
The first trimester
In fact, it makes up nearly half of the fetus' weight at this point. For comparison, by the time your baby is born, the brain is only 10 percent of their body weight. In the first trimester, the brain will grow millions of neurons, which connect across synapses to direct movement and growth.
Which trimester is the hardest? ›
The third trimester is the final stage of pregnancy and can be considered to be the most painful. During this stage, your baby is getting bigger, which puts more stress on your body that causes aches and discomfort.
When does a fetus become a baby? ›
As pregnancy progresses the embryo becomes a fetus. The fetus becomes a neonate or newborn at birth. It may not be common to hear a pregnant person speak about their embryo or fetus in those terms, but we can all choose to use the words we are most comfortable with.
Do and don'ts in the first trimester? ›
The do's during the first trimester of pregnancy include getting prenatal care and maintaining your health, rest and mental health; the don't include drinking alcohol, smoking, using drugs, eating dangerous foods and engaging in risky behaviors.
Why is week 10 of pregnancy the worst? ›
Your nausea and vomiting may be worse than ever: Morning sickness peaks around 9 or 10 weeks of pregnancy for many women. That's when levels of the pregnancy hormone human chorionic gonadotropin (hCG) are highest (morning sickness is thought to be linked to rises in hCG and estrogen).
3 Fruits to Avoid During Pregnancy First Trimester
- Grapes. There are mixed opinions about grapes when it comes to fruits to avoid during pregnancy first trimester. ...
- Unripe and Semi-Ripe Papaya Fruit. ...
- Pineapple. ...
- More Tips About Eating Fruit when Pregnant. ...
- Apples. ...
- Oranges. ...
- Bananas. ...
- Avocados.
Don't eat mould-ripened soft cheese, such as brie, camembert and chevre (a type of goat's cheese) and others with a similar rind. You should also avoid ricotta, feta, mozzarella, bocconcini and blue-veined cheeses. These may contain listeria, which can get in during the manufacturing process.
What not to drink during pregnancy? ›
Coffee, tea, soft drinks, and cocoa all contain caffeine. Research has linked a high intake of caffeine to a risk of pregnancy loss, stillbirth, small weight at birth, and various developmental issues. Caffeine is absorbed very quickly and passes easily into the placenta.
What is a silent miscarriage? ›
A missed (or silent) miscarriage is one where the baby has died or not developed, but has not been physically miscarried. In many cases, there has been no sign that anything was wrong, so the news can come as a complete shock.
Which gender causes extreme tiredness during early pregnancy? ›
The energy demands on your body can result in pregnancy exhaustion and fatigue. As a side note, it's said that extreme tiredness during early pregnancy can indicate the gender is a girl because carrying girls more often results in higher likelihood of nausea and extreme fatigue.
How to know if baby is ok in womb? ›
Signs of a Healthy Pregnancy – Maintaining the Good Antenatal...
- 2.1 Consistent Growth Patterns.
- 2.2 Maternal Weight Gain.
- 2.3 Foetal Movement.
- 2.4 Foetal Heartbeat.
- 2.5 Foetal Position.
Your Child's Development -- Month by Month
| Gross Motor |
|---|
| 4 months | Pushes up on arms when lying on tummy |
| 5 months | Begins to roll over in one or the other direction |
| 6 months | Rolls over both ways |
| 7 months | Moves around --is starting to crawl, scoot, or “army crawl” |
8 more rowsFeb 27, 2024
Fetal brain activity is largely mature by the end of the second trimester, which is when babies first become able to survive outside the womb.
When does a fetus get a heartbeat? ›
At the end of the 4th week of gestation, the heartbeats of the embryo begin. The heart, whose development starts at the 3rd week of gestation, has rapid and irregular contractions capable of pumping the blood inside the vessels.
