Stages of pregnancy from the first to third trimester

Medically reviewed: 6, January 2024

The stages of pregnancy

Pregnancy is a wonderful and exciting journey that lasts about 40 weeks, or nine months. During this time, your body and your baby go through many changes, as they prepare for the birth. Pregnancy is divided into three stages, called trimesters, each lasting about 13 weeks. In each trimester, you and your baby experience different physical and emotional developments, and face different challenges and opportunities.

How is my baby growing? What is happening to my body now that I’m pregnant? When can I expect to see my body change and my baby grow? Pregnancy is a time of many changes and growth for you and your baby. Sometimes it’s easier to prepare for these events and milestones if you know what to expect.

In this article, we will explain what happens in each stage of pregnancy, and how you can take care of yourself and your baby. We will also provide you with some tips and resources to help you cope with the common symptoms and issues that may arise during pregnancy. Whether you are a first-time mom or a seasoned parent, we hope that this article will help you enjoy and appreciate this amazing period of your life.

First trimester (week 1 to week 12)

The first trimester is the most critical stage of pregnancy, as this is when your baby’s organs and body systems start to form. The baby is also growing rapidly in size and weight, from a tiny cluster of cells to a fetus that can be seen on an ultrasound. The first trimester is also the most challenging stage for many women, as they may experience nausea, fatigue, mood swings, and other unpleasant symptoms. The risk of miscarriage is also highest in the first trimester, so it is important to take extra care of your health and well-being.

Some of the milestones and events that happen in the first trimester are:

• Conception:

This is when the sperm fertilizes the egg, and a new life begins. Conception usually occurs about two weeks after the first day of your last menstrual period, but it can vary depending on your cycle length and ovulation date. You may not know that you are pregnant until you miss your next period, or take a pregnancy test.

• Implantation:

This is when the fertilized egg attaches itself to the lining of your uterus, and starts to receive nutrients and oxygen from your blood. Implantation usually occurs about six to 12 days after conception, and it may cause some spotting or cramping, which is normal and harmless. This is also when the placenta, the organ that connects you and your baby, begins to form.

• Hormonal changes:

This is when your body produces high levels of hormones, such as human chorionic gonadotropin (hCG), estrogen, and progesterone, to support your pregnancy. These hormones can cause various symptoms, such as nausea, vomiting, breast tenderness, increased urination, food cravings or aversions, and mood swings. These symptoms usually peak around week eight or nine, and then subside gradually.

• Prenatal care:

This is when you visit your doctor or midwife for the first time, and confirm your pregnancy. You will have a physical exam, a blood test, a urine test, and possibly an ultrasound, to check your health and your baby’s development. You will also get some advice on nutrition, exercise, supplements, and lifestyle changes, to help you have a healthy pregnancy. You will have regular prenatal visits throughout your pregnancy, to monitor your progress and address any concerns.

• Fetal development:

This is when your baby grows and develops at an amazing rate. By the end of the first trimester, your baby will have a heartbeat, a brain, a spinal cord, a face, arms, legs, fingers, toes, and internal organs. Your baby will also be able to move, kick, and swallow, although you may not feel it yet. Your baby will measure about 7.5 centimeters (3 inches) long, and weigh about 28 grams (1 ounce).

Mother

You may not be aware you are pregnant, especially for the first six weeks:

• Food cravings
• Morning sickness
• Mood swings
• Breasts may swell and ache
• Feelings of fatigue, lack of energy
• More frequent constipation
• Increased urination
• By end of trimester you will be able to feel your uterus above your pubic bone
• Weight gain: 2-5 pounds

Fetus development at the first trimester

• Brain and spinal cord are forming
• Lungs and heart are beginning to grow
• Legs, arms, fingers, and toes are forming
• Head is much larger than body
• Heart begins to beat by the 25th day
• Mouth forms 20 buds that later become teeth
• By end of trimester baby is four inches long and weighs about one ounce

Second trimester (week 13 to week 27)

The second trimester of pregnancy is often the most enjoyable, as many of the unpleasant symptoms of the first trimester subside, and you start to feel more energetic and comfortable. The second trimester is also an exciting time, as you can find out the sex of your baby, feel your baby move, and see your baby’s features on an ultrasound.

However, the second trimester also brings some new challenges and concerns, such as weight gain, back pain, and gestational diabetes. The second trimester is a crucial period for your baby’s growth and development, as he or she becomes more active and responsive.

Some of the milestones and events that happen in the second trimester are:

• Fetal movement:

Around week 16 to week 20, you might start to feel your baby move inside your womb. This is called quickening, and it can feel like fluttering, kicking, or tumbling. At first, you might not be sure if it is your baby or your digestion, but as your baby grows bigger and stronger, the movements will become more noticeable and frequent. Feeling your baby move is a reassuring sign that he or she is healthy and happy. You can also try to communicate with your baby by gently rubbing your belly, playing music, or talking to him or her.

• Fetal sex:

Around week 18 to week 22, you might be able to find out the sex of your baby, if you want to. This can be done by an ultrasound scan, which can show your baby’s genitals, or by a blood test, which can detect your baby’s chromosomes. Knowing the sex of your baby can help you bond with him or her, and prepare for his or her arrival. However, some parents prefer to keep it a surprise, and wait until the birth to find out. The choice is yours, and there is no right or wrong answer.

• Anatomy scan:

Around week 20, you will have a detailed ultrasound scan, called an anatomy scan, to check your baby’s growth and development. The scan can show your baby’s organs, bones, muscles, and blood vessels, and measure his or her size and weight. The scan can also detect any abnormalities or defects, such as spina bifida, cleft lip, or heart problems. The scan can also confirm the sex of your baby, if you want to know. The anatomy scan is an important and exciting part of your prenatal care, as it can give you a glimpse of your baby’s appearance and personality.

• Glucose screening:

Around week 24 to week 28, you will have a blood test, called a glucose screening, to check your blood sugar level. This is done to screen for gestational diabetes, a condition that causes high blood sugar during pregnancy. Gestational diabetes can affect your health and your baby’s health, and increase the risk of complications, such as preterm labor, preeclampsia, or macrosomia (large baby). Gestational diabetes can be managed with diet, exercise, and medication, if needed. If your glucose screening is abnormal, you will need a follow-up test, called a glucose tolerance test, to confirm the diagnosis.

• Fetal development:

During the second trimester, your baby continues to grow and develop at a rapid pace. By the end of the second trimester, your baby will have hair, eyebrows, eyelashes, and nails. Your baby will also have a sense of taste, smell, hearing, and touch, and will respond to your voice and other sounds. Your baby will also develop a sleep-wake cycle, and have periods of activity and rest. Your baby will measure about 36 centimeters (14 inches) long from crown to heel, and weigh about 900 grams (2 pounds).

Mother

• Weight gain increases
• Breasts still large, but less tender
• May need to urinate less often than in previous months
• Nausea and vomiting usually lessen
• More energy
• Increase in appetite
• Possible swelling of hands, ankles, and feet
• Pulse increases
• May feel shortness of breath
• Top of uterus continues to rise in your abdomen; by 16th week you may start to “show”
• Light or dark patches may appear on facial skin
• May have dark line down middle of your belly
• Braxton Hicks (“practice”) contractions
• Stretch marks may appear on belly and breasts; skin may itch as it stretches
• Legs may get cramps at night

Baby in second trimester

• Eyelashes and eyebrows develop
• Fingers, fingernails, and toes are well defined
• Baby can make a fist
• By end of 17th week baby may begin to move
• By end of 28th week baby can kick, cry, suck his or her thumb
• Skin is very wrinkly and covered with thick, white coating called vernix
• Has active and quiet times
• Hair starts to grow on head
• Eyelids open and close; eyes almost completely developed
• Baby can hiccup
• By the end of second trimester baby will weigh about 2 pounds and be up to 14 inches long

Third trimester (week 28 to week 40)

The third trimester of pregnancy is the final stage, as you prepare for the birth of your baby. The third trimester is also the most challenging, as you may experience more discomfort, fatigue, and anxiety. The third trimester is a crucial period for your baby’s growth and development, as he or she gains weight, develops more fat and muscle, and matures his or her organs and systems.

Some of the milestones and events that happen in the third trimester are:

• Fetal position:

Around week 32 to week 36, your baby will likely settle into a head-down position, ready for delivery. This is called cephalic presentation, and it makes labor and birth easier and safer. However, some babies may remain in a breech position, where the buttocks or feet are pointing down. This can make delivery more difficult and risky, and may require a cesarean section. Your doctor or midwife may try to turn your baby manually, by applying pressure on your abdomen. This is called external cephalic version, and it can be successful in some cases.

• Fetal growth:

During the third trimester, your baby will grow rapidly, gaining about half a pound (250 grams) per week. Your baby will also develop more fat and muscle, to keep warm and strong. By the end of the third trimester, your baby will measure about 50 centimeters (20 inches) long from crown to heel, and weigh about 3.4 kilograms (7.5 pounds).

• Fetal development:

In the third trimester, your baby will continue to develop and mature his or her organs and systems. Your baby’s brain, lungs, liver, and immune system will be the last to fully develop, and they will keep growing even after birth. Your baby’s senses will also become more refined, and he or she will be able to see, hear, smell, taste, and touch. Your baby will also develop a regular sleep-wake cycle, and have dreams and memories.

•  Fetal testing:

In the third trimester, you may have some tests to check your baby’s health and well-being. These tests may include:

• Nonstress test

This is a test that measures your baby’s heart rate and movements, using a device called a fetal monitor. The test is done to check if your baby is getting enough oxygen and blood flow, and if he or she is responding to stimuli. The test is usually done after week 28, or earlier if you have a high-risk pregnancy.

• Biophysical profile:

This is a test that combines a nonstress test with an ultrasound scan, to assess your baby’s heart rate, movements, breathing, muscle tone, and amniotic fluid level. The test is done to check your baby’s overall condition, and to identify any signs of distress or complications. The test is usually done after week 32, or earlier if you have a high-risk pregnancy.

• Contraction stress test:

This is a test that measures your baby’s heart rate and movements, while you have contractions, either naturally or induced by a drug called oxytocin. The test is done to check how your baby reacts to the stress of labor, and to detect any signs of placental insufficiency, which is a condition where the placenta does not provide enough oxygen and nutrients to your baby. The test is usually done after week 34, or earlier if you have a high-risk pregnancy.

Labor and delivery at third trimester stage of pregnancy

This is the final and most anticipated event of your pregnancy, when you give birth to your baby. Labor and delivery can vary in duration, intensity, and method, depending on your health, your baby’s health, and your preferences. Labor and delivery can be divided into three stages:

• First stage:

This is the stage when your cervix dilates, or opens, from 0 to 10 centimeters, to allow your baby to pass through. This stage can last from a few hours to a few days, and it is usually the longest and most painful stage. You may experience contractions, which are rhythmic tightening and relaxing of your uterine muscles, that become stronger, longer, and closer together as labor progresses.

You may also have a bloody show, which is a discharge of mucus and blood from your cervix, and your water may break, which is a rupture of the amniotic sac that surrounds your baby. You may feel the urge to push, but you should wait until your cervix is fully dilated, to avoid tearing or exhaustion.

• Second stage:

This is the stage when you push your baby out of your uterus and vagina, with the help of your contractions and your doctor or midwife. This stage can last from a few minutes to a few hours, and it is usually the most intense and rewarding stage. You may feel a burning or stretching sensation, as your baby’s head crowns, or emerges from your vagina.

You may also need an episiotomy, which is a surgical cut in your perineum, the area between your vagina and anus, to make more room for your baby. Once your baby is born, he or she will be placed on your chest, and the umbilical cord will be cut.

• Third stage:

This is the stage when you deliver the placenta, the organ that nourished and supported your baby during pregnancy. This stage can last from a few minutes to a half hour, and it is usually the easiest and least painful stage. You may have some mild contractions, as your uterus contracts and expels the placenta. You may also have some bleeding, as your uterus heals and shrinks. You may need some stitches, if you had an episiotomy or a tear. You may also start breastfeeding, if you choose to, as this can help your uterus contract and reduce bleeding.

What does mother feel?

• Belly rapidly increases in size
• Easier to lose balance and fall
• Hip joints are looser and may ache
• May get dizzy if you stand up suddenly
• May feel kicks against ribs and see belly bulge when baby moves
• Colostrum (first milk) may leak from breasts
• Hands and feet may swell slightly
• May feel very warm
• May need to urinate often
• Top of uterus pressing against ribs, may have shortness of breath
• Baby drops into pelvis before birth
• May feel very tired
• Just before labor starts, may feel a burst of energy

How does baby grow in the third trimester

• Baby grows quickly
• Activity may increase
• Body is well formed
• Can open eyes and see light
• Fingernails grow
• Baby has a good chance of surviving if born after end of seventh month
• Most babies grow to about 20 inches and 7 pounds or more by the end of third trimester.