Pregnancy Trimesters: Stages Of Pregnancy, Symptoms And Prenatal Care

Updated:June 25, 2025 | Published:December 17, 2024 | ByPamela Li

Pregnancy trimesters are the stages of pregnancy that are divided into first, second, and third trimesters. The first trimester is from the first day of the woman’s last menstrual cycle until the end of the 12th week. The second trimester starts from week 13 until the end of the 28th week. The third trimester starts from week 29 until the mother gives birth. Understanding how many trimesters are in a pregnancy helps monitor the different stages of fetal development and maternal changes.

Pregnancy symptoms include nausea and vomiting, fatigue, breast changes, frequent urination, mood swings, weight gain, swelling, leg cramps, heartburn, Braxton-Hicks contractions, and difficulty sleeping. Hormonal changes cause an uneasy stomach, while fatigue is expected in the first and third trimesters. Breast changes, frequent urination, mood swings, weight gain, swelling, leg cramps, heartburn, and Braxton-Hicks contractions affect pregnancy, according to a 2013 study from Australia titled “Development and validation of a pregnancy symptoms inventory,” conducted by Foxcroft et al. at Queensland University of Technology and published in BMC Pregnancy and Childbirth. Managing symptoms and knowing the pregnancy timeline aid in a healthy pregnancy.

The best prenatal care for the three trimesters in pregnancy includes taking prenatal vitamins, maintaining a balanced diet, staying hydrated, exercising regularly, monitoring weight gain, and attending prenatal appointments. Prenatal care in the stages of pregnancy helps prevent birth defects and aids in baby development. Different medical monitoring and lifestyle modifications are needed at different trimesters of pregnancy to protect the mother’s and the unborn child’s health and well-being.

What are the trimesters of pregnancy?

The trimesters of pregnancy are the first, second, and third trimesters. The first trimester is from the first day of the woman’s last menstrual cycle until the end of the 12th week. The second trimester starts from week 13 until the end of the 28th week. The third trimester starts from week 29 until the mother gives birth.

1. First Trimester

The first trimester marks the foundation for the mother’s and baby’s development. First-trimester symptoms during the first trimester include fatigue, nausea, sensitive or swollen breasts, frequent urination, and mood swings. The first day of the last menstrual cycle is when the first trimester starts, and the first trimester in pregnancy ends at the end of the 12th week (months one through three).

Doctors’ recommendations for the first trimester weeks include eating a balanced diet, drinking plenty of water, getting lots of rest, and abstaining from drugs and alcohol. Prenatal vitamins, including folic acid, are needed for the unborn child’s growth during early pregnancy. Regular check-ups with a healthcare provider are required to monitor the pregnancy and handle any issues. Avoid alcohol-containing beverages, tobacco products, recreational drugs, and specific foods, including raw fish, unpasteurized dairy products, or seafood high in mercury.

Pregnant women experience an array of symptoms during the first trimester of pregnancy due to hormonal changes. Morning sickness happens at any time and is often accompanied by vomiting. Fatigue is one of the first trimester pregnancy symptoms, as the body works hard to support the growing fetus. Elevated hormone levels cause breasts to become tender and swollen. The expanding uterus causes frequent urination, and some women have food cravings, aversions, and increased sensitivity to specific smells. Hormonal surges cause mood swings.

The brain and spinal cord of the fetus begin to mature, and the embryo’s heart begins to beat toward the end of the first month or the beginning of the second month. The fetal development during the first trimester in pregnancy is marked by rapid changes as the fertilized egg, now a zygote, undergoes numerous cell divisions and implants into the uterine wall. The first trimester fetal development is where the placenta forms and functions in addition to supplying nutrients and oxygen. The fetus is fully developed by the end of the first trimester, weighing around half an ounce and measuring about four inches in some studies. A 12-week fetus measures 5.3-6.6 centimeters from head to bottom or crown-rump length (CRL), roughly 2.5 inches, according to a 1992 study, “Fetal Crown-Rump Length: Reevaluation of Relation to Menstrual Age (5-18 weeks) with High-Resolution Real-Time US,” by Hadlock, F. P., et al., published in Radiology.

2. Second Trimester

The second trimester is the midpoint of pregnancy trimesters, characterized by significant fetal growth and development and observable changes in the mother’s body. Week 13 is when the second trimester starts, and the end of week 28 is when the second trimester ends (months four through seven). This middle trimester represents the change from the early to the more mature stages of fetal development, during which the fetus gets more active and its features become clearer.

The development of the fetus’s organs and systems, such as the alignment of facial features and the precise definition of fingers and toes, is the fetal development during the second trimester of pregnancy. The second trimester fetal development is expected for the baby to be able to stretch, make expressions, or even suck its thumb by the fourth month. The baby develops eyelids, eyebrows, eyelashes, nails, and hair. The fetus recognizes sounds by the end of the second trimester and reacts to the mother’s speech, according to a 2015 study from the UK, titled “Fetal Behavioural Responses to Maternal Voice and Touch,” conducted by Viola Marx et al. at the University of Dundee and published in Plos One.

Symptoms of the second trimester include leg cramps, dizziness, nasal congestion, growing breasts and tummy, skin changes, Braxton-Hicks contractions, and dental problems. Expectant mothers report feeling more hungry and sometimes even feeling the fetus move, characterized as fluttering as part of the second-trimester symptoms. Doctors’ recommendations for the second trimester include eating a balanced diet, drinking plenty of water, taking prenatal vitamins, going to routine prenatal checkups, exercising cautiously, avoiding heavy lifting, and getting lots of rest. Reducing stress and keeping up with physical changes makes the second-trimester stage easier for expectant mothers.

3. Third Trimester

The third trimester is the final phase of pregnancy, starting at week 29 and lasting until the baby’s birth (months seven through ten). The baby experiences enormous growth with third trimester fetal development. The mother experiences various physical and psychological changes. The brain, lungs, kidneys, and breathing patterns are the organs and systems that the fetus develops. The fetus weighs between six and nine pounds and is 19 to 21 inches long at the end of the third trimester.

Backaches, heartburn, shortness of breath, frequent urination, Braxton Hicks contractions, swelling in the hands, cheeks, and ankles, and trouble sleeping are the distinct 3rd trimester pregnancy symptoms. These third-trimester symptoms are detailed in a 2017 study from The United States, titled “Symptom Experience in Late Pregnancy,” conducted by Kathleen R. Beebe et al. at the University of California and published in the Journal of Obstetric, Gynecologic & Neonatal Nursing. Keep an eye on the health of the mother and the baby. Routine prenatal exams are advised. Keep a nutritious diet, remain hydrated, and get lots of sleep. Heavy lifting must be avoided by pregnant women, and relaxation techniques are recommended to reduce tension.

The 28th week is when the third trimester starts. It is the period where the baby’s organs mature, and the body gains weight and strength. The mother experiences various physical changes and symptoms, such as increased abdominal size and preparation for labor, as the body readies itself for the upcoming delivery. The baby’s birth, or around 40 weeks of pregnancy, is when the third trimester ends.

The third trimester weeks are marked by the mother’s increasing abdomen, aches and pains. The extra fat the baby stores for warmth at birth accompanies the weight gain. The third trimester in pregnancy brings expectations such as increased difficulty breathing, lower back pain, frequent urination, difficulty falling asleep, breast leaking colostrum, the fetus lightening, and labor indicators such as contractions or the loss of the mucus plug.

Why is Pregnancy Divided into Three Trimesters?

Pregnancy is divided into three trimesters to simplify the understanding of different stages of prenatal development and manage the health of the mother and the developing fetus. The trimester represents fetal development and maternal change, allowing healthcare providers to focus on specific milestones and health concerns about pregnancy. The first trimester is for early organ formation and establishing a healthy pregnancy.

The second trimester emphasizes the growth and refinement of fetal features. The third trimester focuses on preparing the fetus for birth and labor preparations. The pregnancy stages help assess pregnancy progress and ensure maternal and fetal well-being.

The chance of spontaneous abortion increases throughout the first trimester and decreases in the second and third trimesters. The second trimester provides easier fetal growth and development monitoring, and the third trimester indicates fetal viability. Pregnancy is the state of fertilization and development for one or more offspring within a woman’s uterus. The average time for childbirth is 35 weeks after conception (37 weeks in gestation). Women with menstrual cycles that last four weeks or more have childbirth about 40 weeks after the last regular menstrual period.

What is the Importance of Understanding Each Trimester for a Healthy Pregnancy?

The importance of understanding each trimester for a healthy pregnancy is to allow pregnant mothers and healthcare providers to accurately monitor the baby’s development and handle the mother’s changing requirements. Specialized medical care and lifestyle modifications are necessary because of each trimester’s distinct physiological changes and developmental milestones.

Expectant moms are able to make educated decisions, heed medical advice when needed, and develop healthy behaviors that promote the health of mother and child throughout the pregnancy cycle, being aware of each stage. Immediate prenatal cycle care and lifestyle adjustments are required during the first trimester, covering pregnancy by weeks 1 to the end of week 12. First-trimester prenatal care is essential due to the development of organs and a higher chance of miscarriage. The second trimester is more comfortable for the mother, but monitoring the baby’s progress and the mother’s health helps identify any problems early. The third trimester is dedicated to labor and delivery, emphasizing the mother’s physical preparedness and the baby’s positioning.

What are the Common Pregnancy Symptoms throughout the Whole Pregnancy?

The common pregnancy symptoms throughout the whole pregnancy are listed below.

• Fatigue: Pregnancy fatigue is common in the first and third trimesters. It is associated with anemia or the baby’s increasing energy requirements. Pregnant women must get adequate sleep, adhere to a routine, balance diet and relaxation, and moderate exercise.
• Frequent Urination: Hormonal fluctuations and the expanding uterus are linked to frequent urination. Higher levels of hCG and progesterone throughout the first and third trimesters raise bladder pressure.
• Mood Swings: Mood swings during pregnancy are associated with hormonal changes, including increased estrogen and progesterone, fatigue, sleep deprivation, and anxiety. The emotional fluctuations are normal and subside after childbirth.
• Weight Gain: Pregnancy is a natural process involving weight gain. The recommended weight gain for underweight women is 28-40 pounds, normal weight women 25-35 pounds, overweight women 15-25 pounds, and obese women 11-20 pounds, according to the 2009 Insitute of Medicine (IOM) Gestational Weight Gain Guideline. The weight is distributed among the baby, placenta, breast tissue, blood supply, and fat stores for breastfeeding. Maintaining a healthy lifestyle helps maintain weight.
• Swelling: Pregnancy causes swelling in various areas, including the face, hands, legs, ankles, and feet. The swelling is due to increased blood and fluid production, causing fluid buildup. Management involves staying hydrated, elevating feet, and avoiding prolonged sitting or standing.
• Heartburn: Heartburn is a common pregnancy symptom linked to hormonal changes. The changes allow stomach acid to escape the esophagus, and pressure on the stomach worsens the condition as the uterus grows.
• Difficulty Sleeping: Pregnant women experience difficulty sleeping, likely due to hormonal changes, physical discomfort, frequent urination, and anxiety. Strategies to improve sleep quality include regular sleep schedules, supportive pillows, and relaxation techniques.

Are Hormonal Changes Significant in All Three Trimesters?

Yes, hormonal changes are significant in all three trimesters in pregnancy. Early pregnancy symptoms, including nausea, mood changes, and fatigue, are associated with a large increase in progesterone and estrogen levels in the first trimester. Estrogen continues to rise throughout the second trimester and is needed to form the breast’s milk ducts and preserve the uterine lining.

Estrogen levels rise in the third trimester as the body prepares for labor and delivery. Hormones such as relaxin loosen the pelvic ligaments, facilitating the baby’s passage into the birth canal. Changes in hormones affect the mother physically and psychologically. Hormonal rises are necessary for the development of the fetus and the course of the pregnancy.

Hormones such as progesterone and estrogen aid in the growth of the uterus and prepare the body for lactation throughout the second trimester. Changes affect skin, hair, and mood. Many women experience a decrease in morning sickness during the second trimester.

Which Trimester Do Hormones Have the Greatest Impact?

The first trimester is when hormones have the greatest impact. There is a surge in progesterone, estrogen, and human chorionic gonadotropin (hCG) levels. These pregnancy hormones are needed to establish and maintain pregnancy, support the embryo, and prevent menstruation. Hormonal fluctuations aid in the successful pregnancy progression but often cause physical and emotional changes in the mother.

Early pregnancy symptoms include nausea, fatigue, mood swings, and breast tenderness. The rapid increase in estrogen levels is needed for the development of the fetus and the preparation of the mother’s body for pregnancy. High levels of progesterone help maintain the uterine lining and prevent contractions. The first trimester is when hormones’ most noticeable impact is felt.

What are the Common Complications in Each Trimester of Pregnancy?

The common complications in the 3 trimesters of pregnancy are listed below.

• Miscarriage: Miscarriage occurs before the 20th week due to chromosomal abnormalities, causing symptoms such as vaginal bleeding, cramping, and tissue passing.
• Gestational Diabetes: Gestational diabetes, a condition causing high blood sugar levels, leads to pregnancy complications such as high birth weight and increased risk of type 2 diabetes. Gestational diabetes occurs in the second trimester, between the 24th and 28th weeks.
• Preeclampsia: Preeclampsia, a severe pregnancy complication, causes high blood pressure, liver and kidney damage, and severe symptoms after the 20th week.
• Vaginal Bleeding: Vaginal bleeding is one of the pregnancy complications occurring for various reasons, such as implantation, cervical polyps, or severe conditions, including miscarriage or ectopic pregnancy. Vaginal bleeding tends to occur in the first trimester, but it is possible to happen at any stage of pregnancy.
• Placenta Previa: Placenta previa, a pregnancy complication where the placenta covers the cervix, causes severe bleeding and needs a cesarean delivery. Placenta previa is mainly diagnosed in the second trimester.
• Low Amniotic Fluid: Low amniotic fluid, or oligohydramnios, is a condition in which the baby’s amniotic fluid is lower than expected, leading to complications during pregnancy. It is primarily diagnosed in the third trimester, especially if the pregnancy goes past the due date.

Is the Risk of Miscarriage the Highest in the First Trimester?

Yes, the risk of miscarriage is the highest in the first trimester of the three pregnancy trimesters. The first trimester of pregnancy, which lasts for the first 12 weeks, is when the chance of miscarriage is highest. The embryo undergoes significant changes and grows quickly during this crucial stage, which leaves it open to many situations that result in loss. The first trimester results in approximately 80% of miscarriages, according to a 2018 study from the United States titled “Miscarriage,” by Dugas, Carla et al., published in StatPearls Publishing. The majority of miscarriages happen before 8.5 weeks, according to a 2005 study from the United States, titled “Evidence-based Care of Recurrent Miscarriage,” by  T. Flint Porter et al., published in Best Practice & Research Clinical Obstetrics & Gynaecology.

Chromosome abnormalities, hormone imbalances, uterine abnormalities, and certain medical diseases such as thyroid disorders and diabetes tend to be the leading causes of early miscarriages. The chance of miscarriage greatly drops as the pregnancy goes past the first trimester, improving the odds of a healthy pregnancy.

Pregnancy loss is possible even before a person is aware that they are carrying a child. A woman has a 15.3% risk of recognized pregnancy, according to a 2021 study titled “Miscarriage Matters: The Epidemiological, physical, psychological, and Economic Costs of Early Pregnancy Loss,” by Siobhan Quenby et al., published in The Lancet. Genetic problems are one of the causes of miscarriages early in pregnancy, yet circumstances beyond the person’s control cause the majority of pregnancy losses. The first trimester is the most vulnerable as the pregnancy advances into the second and third trimesters when the chance of miscarriage declines.

What are the Best Prenatal Care Tips for Each Trimester of Pregnancy?

The best prenatal care tips for the trimesters of pregnancy are listed below.

• Take Prenatal Vitamins, as Directed by OBGYN: Prenatal vitamins are needed for the mother’s health and the baby’s development during the first trimester of pregnancy. It includes folic acid, iron, calcium, vitamin D, omega-3 fatty acids such as DHA and EPA, iodine, choline, vitamin A, vitamin C, vitamin B6, and vitamin B12. The vitamins prevent neural tube defects, support increased blood production, and aid bone and teeth development. Daily intake helps fill nutritional gaps and promotes a healthy pregnancy. Follow instructions from your OBGYN on which one and how many prenatal vitamins to take.
• Prepare for Birth: Birth preparation during the third trimester of pregnancy includes attending childbirth education classes, creating a birth plan, and packing essentials. Discussing pain management options with healthcare providers during prenatal care and arranging support during and after delivery help reduce anxiety and ensure a smoother birthing experience.
• Eat a Balanced Diet: A balanced diet during the first trimester of pregnancy is needed for the mother’s and baby’s healthy development. It includes fruits, vegetables, whole grains, and lean proteins. A balanced diet provides nutrients rich in essential vitamins and minerals, including folic acid, iron, calcium, and protein. A balanced diet supports the baby’s growth and influences pregnancy symptoms.

Why is Prenatal Care the Most Significant in the First Trimester?

Prenatal care is the most significant in the first trimester because it detects early complications, establishes a healthy foundation for the pregnancy, and supports the development of the baby’s organs. Prenatal care in the first trimester of pregnancy supports the foundation for the baby’s brain, heart, spinal cord, and other important organs. The fetus is most susceptible to infections, poisons, and other dangerous chemicals in the first trimester, which negatively affect the growth and development of the baby.

Pregnancy care that begins early allows medical professionals to monitor the mother’s health, treat any pre-existing illnesses, and offer advice on lifestyle, diet, and risk avoidance. Maintaining a good diet, getting regular exercise, and limiting exposure to toxic substances help expectant mothers lower the probability of experiencing pregnancy-related problems.

Do the Nutritional Needs for a Mother Change Across the Three Trimesters?

Yes, the nutritional needs of a mother do change across the three trimesters of pregnancy. The first trimester of pregnancy is dedicated to maintaining an appropriate intake of nutrients such as folic acid, iron, and calcium, supporting the early development of organs and systems. The mother’s daily calorie requirements rise by about 340 kcal during the second trimester and 450 kcal during the third trimester to support the developing baby, according to a 2003 study from the United States titled “Pregnancy and Lactation: Physiological Adjustments, Nutritional Requirements and the Role of Dietary Supplements,” conducted by Picciano Mary Frances at National Institutes of Health and published in The Journal of Nutrition. Protein consumption is raised to support the growth of fetal organs and tissues.

The baby’s rapid development and weight gain during the third trimester cause the caloric needs to increase every day. The mother’s increasing blood volume and the baby’s bone development require higher nutrient requirements for vitamins and minerals, including calcium and iron. A well-balanced diet rich in nutritious foods helps throughout pregnancy to fulfill the fluctuating nutritional needs of mother and baby.

How Often Should You Have Prenatal Visits at Each Trimester of Pregnancy?

You should have prenatal visits every 4 weeks (monthly) during the first and second trimesters, every 2 weeks (biweekly) until 36 weeks, and weekly until delivery, according to the 2017 Guidelines from the American College of Obstetricians and Gynecologists (ACOG), detailed in a 2020 study titled “The evolution of prenatal care delivery guidelines in the United States,” published in the American Journal of Obstetrics and Gynecology.

The number of prenatal visits during a healthy pregnancy follows a set timetable. It is advised to have one checkup every four weeks throughout the first and second trimesters, which run from weeks 1 to 28. One visit every two weeks becomes expected as the mother enters the third trimester, which spans weeks 29 to 36. One visit each week during weeks 37 to childbirth in the third trimester is advised.

The visits have significance for monitoring the mother’s and baby’s development and well-being. Healthcare professionals monitor blood pressure, weight, urine, and the baby’s growth. The routine examinations aid in the early detection of potential issues and offer advice on keeping a pregnancy healthy. Regular visits allow problems to be quickly resolved as the deadline draws near.

A checklist is usually provided in every appointment to assist the mother in moving closer to a healthy outcome for both mother and child. The appointments offer chances for instruction, evaluation, and assistance. The initial visit includes a comprehensive physical examination and a pelvic exam. A check-up or ultrasound ensures the baby is developing healthily inside the uterus.

What are the Specific Tests Recommended during Each Trimester of Pregnancy?

The specific tests recommended during each trimester of pregnancy include a blood test, ultrasound, and genetic screening in the first trimester. An anatomy scan and glucose tolerance test in the second trimester. A Group B Strep test, fetal monitoring, and an ultrasound to assess the baby’s position and growth in the third trimester.

Blood testing during the first trimester is essential for a successful pregnancy. Human chorionic gonadotropin (hCG), a hormone made by the developing placenta, is detected early on, confirming the pregnancy. Ultrasounds confirm pregnancy and identify fetal heartbeat, gestational age, and multiple pregnancies. Genetic screening at 11-14 weeks includes first-trimester blood, cell-free fetal DNA, and nuchal translucency ultrasounds. The tests help make decisions and prepare for actions about chromosomal diseases such as Down syndrome and trisomy 18.

Second-trimester anatomy scans, glucose tolerance tests, and genetic testing are part of pregnancy monitoring. The anatomy scan detects congenital abnormalities in the baby’s organs and tissues. The glucose tolerance test detects gestational diabetes, preventing excessive birth weight and preeclampsia.

Healthy pregnancies require GBS tests, fetal monitoring, and ultrasounds in the third trimester. GBS testing detects dangerous germs, while fetal monitoring watches heart rate and movements to detect distress. Ultrasounds, or growth scans, assess the baby’s growth, position, and development to ensure a safe and healthy delivery.