All about the trimesters of pregnancy

The amazing journey of pregnancy is filled with excitement, changes, and a range of emotions. This entire journey is broken down into three trimesters, starting with the first symptoms and ending in the last few weeks. Every trimester brings with it special developments for the mother and the unborn child. Gaining an understanding of these modifications can facilitate and lessen the intensity of the experience.

It all starts in the first trimester. When the body begins to change quickly, it’s frequently a period of discovery and adjustment. Many mothers report feeling more energised during the second trimester, which is typically regarded as the most comfortable time. As the baby continues to grow and develop, by the third trimester, plans for the baby’s arrival begin to take center stage.

You can confidently navigate the ups and downs of pregnancy if you know what to expect in each trimester. Every step you take toward meeting your child, whether it’s feeling that first flutter of movement or realizing how your body is preparing for delivery, makes you closer to that moment.

What is it?

Three calendar months are the length of time that makes up a pregnancy trimester. A baby’s birth takes place over the course of nine calendar months, or ten obstetric months. The obstetric month is always equal to 4 weeks, or 28 days, as opposed to one calendar month, which is familiar to us and contains between 28 and 31 days. Three trimesters make up the whole gestational period. There is no such thing as a fourth trimester of pregnancy, which is the clear conclusion to the question.

When more precise and in-depth information regarding the stages of fetal development in the mother’s womb emerged in the 20th century, the division of time into three equal periods was introduced into obstetric practice.

A better understanding of the pregnancy trimesters aids expectant parents in navigating the labor and delivery process with greater ease. Every trimester symbolizes a different stage of the pregnancy, from the beginning to the end of the last preparations for delivery. This article provides information on physical changes, emotional shifts, and significant milestones, breaking down what to expect at each stage. You can better prepare for the changes and growth that accompany each trimester if you have this knowledge.

How to count?

Originally, there was a very antiquated, straightforward method for figuring out the trimester: the total gestational age was calculated and divided by three, yielding three distinct time periods of 14 weeks each. However, using this computation, it was discovered that 42 weeks of pregnancy marked the end of the third and final trimester. Of course, prolonged pregnancies (between 40 and 42 weeks) are not uncommon, but they are also not common. As a result, obstetricians gradually arrived at a more sensible method of counting.

• features and rates of formation of fetal structures and the "baby"s place";
• metamorphosis in the female body;
• exposure to negative factors of influence that can make their own adjustments to the formation of a new life;
• availability of drug therapy and possible other medical interventions to solve current problems with the condition of the child and mother.

Three periods were thus obtained, and these are shown in the table.

Trimester

Weeks in terms

Level of perils and hazards

Initially

Secondly

Third

27–40 (weeks 41 and 42)

If you divide the stages of the baby’s development using this method of division, you will obtain the trimester schedule that is shown below.

Trimester

Procedures

Intrauterine Development Periods

Initially

Placentation, blastogenesis, organogenesis, zygote formation, and fertilization.

Foetal, starting in the ninth week of pregnancy.

Secondly

Systemogenesis, the early birth phase (starting in the 22nd week).

Fetal, perinatal, from the 22nd week.

Third

Development and growth within the uterus.

Perinatal, late fetal birth.

The trimesters are also classified according to the degree of danger in a multifactorial and intricate manner.

Notably, the most hazardous and "critical" ones are:

• the period of implantation and blastogenesis (begin a week after conception and last several days);
• the period of placentation (formation and formation of the placenta);
• the period of organogenesis (formation of internal organs) – 3-9 weeks;
• the beginning of aging of the placenta, increase in its permeability (32-36 weeks).

As a result, the first trimester is the most crucial, with the third trimester’s start posing less risk.

The term of the trimesters cannot be determined by any individual feature. The beginning and ending dates of each trimester cannot be moved in either direction; this division is the same for all pregnant women and does not alter under any circumstances.

First third

It makes sense that the first trimester, which lasts precisely 13 weeks, is the most dangerous. This third of the gestation period is so fast-paced that all processes should be measured in minutes and seconds rather than weeks and days. This is how the first trimester is different from the other two.

What happens?

Pregnancy’s first third is when organogenesis and placentation take place. This indicates that a fully developed complex organism can be created in a constrained amount of time from a single cell, known as a zygote, which is created when two parental cells fuse.

The blastocyst’s implantation and cellular processes take up the first two weeks following conception. As a blastocyst, the unborn child is fixed in the uterus and starts to take in nourishment and oxygen from the mother’s blood.

Her blood vessels are connected to the chorionic villi. The process of placentation—the slow formation of the placenta, which is necessary for the baby’s development—occurs simultaneously with the development of every internal organ. The third week after conception to the eighth week is when this process takes place.

At that point, the baby’s developmental stage ends and it is no longer referred to as an embryo, becoming a fetus.

A specific sequence emerges when we examine the events of the first trimester in greater detail.

• Preimplantation period. Conception has taken place, with the fusion of parental gametes, a diploid zygote was obtained – an absolutely new stem cell with a full set of genetic information about the future little person. It is from it that a new full-fledged organism will appear. This amazing cell moves for about three days along the fallopian tube into the cavity of the female reproductive organ. It quickly becomes two-celled. Its movement is uneven. At the same time, it divides into blastomeres and becomes a morula. The morula descends into the uterine cavity and for about three more days freely floats in it, transforming into a blastocyst. It first sticks to the endometrium, and then begins to sink deeper with the help of the villi of the outer layer. Implantation takes about 40 hours.
• Intrauterine development of the baby. Usually begins on the 9-10th day after conception, when implantation is successfully completed. Formation of three embryonic petals begins. They are to become the internal organs, skeleton, muscles and skin of the baby. When the mother begins the first day of delay, the baby is already two weeks old, and obstetricians believe that she is 4 weeks pregnant. The baby resembles a bubble covered with chorionic cells. Next, you can evaluate the metamorphoses by the main stages.
• Four weeks of pregnancy — the proembryo becomes a full-fledged embryo. The prototype of the placenta is a fluffy and dense accumulation of villi covering the fertilized egg. This cannot protect the baby from negative factors. The very first to be laid are the extraembryonic structures, which should prepare the best environment for the baby"s survival — the yolk sac, tertiary villi.
• Fifth week of pregnancy (3rd week of baby development) — the time of formation of the primary strip, which determines the division into right and left parts, the location of the head and tail is also determined. And the formation of internal organs begins immediately. The first to appear are the neural tube, heart and sex cells. The tiny heart, still only two-chambered, begins to contract on the 21st day after conception, at the end of this obstetric week, and this can already be determined by ultrasound. Simultaneously with the neural tube, the liver, trachea, lungs, primary intestine, primary kidney and pancreas begin to form.
• Sixth week of pregnancy (4 from conception) — the period when the embryonic disk begins to twist into a cylinder, in which the intestinal tube is born. The formation of the prototype of the nervous system begins. The brain and spinal cord are “outlined”. There are rudiments of arms and legs, the heart pulsates and protrudes forward. There are gills – as many as five pairs of arcs. Eyes and a nose are emerging, the baby has learned to bend.
• The seventh week of pregnancy (5 from conception) is the time of brain formation. The first nerve fibers begin to appear, which pass from the organs to the brain and in the opposite direction. The spine gets its first bend. The arms grow faster than the legs. The genital ridges-tubercles appear, so far they are absolutely the same in both boys and girls. The early placenta becomes more complex, the blood supply to the embryo becomes more intense.
• The eighth week of pregnancy (6 from conception) is significant in that the brain and spinal cord are separated, becoming different parts of the central nervous system. The baby can quickly bend and unbend the neck, facial structures begin to develop. There are fingers on the hands. In girls, there are 7 million eggs in the formed ovaries.
• The ninth week of pregnancy (7 from conception) is the time of metamorphosis in the limbs, the fetus has learned to straighten its legs and arms. The baby"s blood begins to produce its own red blood cells, which can enter the mother"s bloodstream. It is on their detection that the non-invasive genetic DNA test is based, which can be carried out after this week to determine chromosomal abnormalities and the sex of the baby.
• The tenth week of pregnancy (8 from conception) – the laying of organs ends. The baby has everything, and now it will all grow and acquire the ability to function. The brain is developing intensively, the baby"s behavior becomes more complex.

By the time the organogenesis period ends, the fetus exhibits incredible skills. It can cover its face with its hands, suck its finger, and, in the event that it senses danger—the woman had chosen to abort the child at this point—it can skillfully avoid obstetric instruments that are inserted into the uterus. The kidneys are functioning and eliminating pee back into the water, allowing the baby to swallow water. The composition of amniotic fluid is replenished every 3–4 hours.

During the first third of pregnancy, the placenta grows bigger than the developing baby. The development of the external genitalia starts in the early fetal period, at the 11th week by obstetric standards, which corresponds to the 9th embryonic week. The baby is growing quickly; it will be nine centimeters tall in two weeks from its current height of roughly five.

The baby’s brain will develop grooves and convolutions, making it "smarter" every day.

A woman’s well-being

One of the hardest trimesters is thought to be the first. The female body’s intense internal processes inevitably impact her condition. While some expectant mothers find this phase relatively easy and do not experience toxicosis, most look forward to the end of the first trimester because they should feel at least somewhat relieved by the second.

The progesterone hormone is linked to a decline in wellbeing during the first three months of pregnancy. Large-scale production occurs from the moment of conception, and human chorionic gonadotropin (hCG) sustains its high level following implantation.

Progesterone plays a critical role in preserving pregnancy by preparing the endometrial layer of the uterus for implantation, storing fat and fluid in the body to "feed" the developing organism, relaxing smooth muscles to prevent increased uterine tone, and suppressing the female immune system’s activity to prevent the embryo from being rejected by the mother’s body’s aggressive protective cells, which would view it as an alien object.

Progesterone also has other side effects, such as causing an unstable mental state in expectant mothers, mood swings that come on suddenly, insomnia, and the relaxation of the uterine, esophageal, and intestinal muscles, which results in heartburn and constipation. Decreased immunity raises the risk of illness and makes chronic diseases worse. The immune system’s reaction to progesterone also contributes to the development of toxicosis.

The health status varies greatly; it can range from extreme toxicosis, which might necessitate the termination of the pregnancy for life-threatening reasons, to mild morning sickness or total lack of unpleasant feelings.

Risks and dangers

There are numerous ways that development during this crucial time could go awry. It has long been known that diseases substantially raise the risk of birth defects in both the mother and the child. For example, a woman who suffers from kidney disease frequently gives birth to children who already have kidney problems at birth, and a mother who has heart defects increases the risk of heart defects in the fetus.

It’s important to remember that every week in the first trimester is risky when discussing which weeks are the most dangerous. Adverse factors that can affect the fetus after 13 weeks can result in organ dysfunction; however, if these same factors impact the organogenesis period specifically, the defects will be severe and occasionally irreversible.

Women who lead unhealthy lifestyles—smoking, drinking alcohol, using drugs—are more likely to have serious defects. Living in environmentally unfavorable areas, working in dangerous industries, coming into contact with radiation or harmful substances, or working in hazardous jobs all increase the risk of fetal pathologies.

The fetus is most at risk from the following factors:

• androgens;
• caffeine;
• indomethacin;
• large amounts of ultraviolet radiation (increases the risk of mutations);
• aspirin (often leads to abnormalities in the structure of facial structures, delayed fetal development);
• excess vitamin A;
• lack of iodine, calcium;
• the presence of diabetes in the mother;
• acute infectious viral diseases.

Due to the risk of catching a viral infection, you should be cautious when taking any medications that have not been prescribed by a doctor and avoid crowded areas.

A mutation may also happen during the zygote formation stage, in which case the pathologies will be chromosomal. Turner syndrome, Edwards syndrome, Down syndrome, and others are among them. Some "errors" that might happen at this time are not compatible with life; early pregnancy termination occurs.

A woman’s medication regimen requires particular attention. Unfortunately, there are occasions when even gynecologists will prescribe certain medications without any apparent reason or consideration for individual characteristics. This increases the risk of developmental anomalies significantly. Excessive consumption of even basic vitamins can have serious, irreversible effects. Pregnant women should not take any completely safe medications found in nature. Water-soluble vitamins and minerals, herbal laxatives, and anti-ulcer medications are a few relatively safe options.

Certain medications belonging to the cephalosporin and penicillin families, enzyme preparations, magnesium sulfate solution, atropine, corticosteroid hormones, diuretics, macrolide antibiotics, and antifungal agents are among the medications that can have a negative impact on the developing foetus. Prohibited under all circumstances due to their strong teratogenic potential: aminoglycosides, chinolons, tetracycline, streptomycin, levomicetin, and sulfanilamides.

Antibiotics are prescribed only after a thorough evaluation of the benefits and drawbacks, including consideration of substances that are categorically contraindicated.

If there are numerous of them, barbiturates, antihistamines, and vitamins should not be taken during the first trimester. Although it would seem that vitamins cannot harm an unborn child, there are some subtle differences. This is what high vitamin dosages can accomplish:

• ascorbic acid – a provocateur of a miscarriage, frozen pregnancy;
• vitamin a – a factor leading to different vices, more often to the vices of the central nervous system, organs of vision, and palate;
• Vitamin E – causes anomalies of the structures of the skeleton and the eyes;
• Vitamin K – leads to the formation of heart defects, blood vessels, nervous system.

Because of this, taking vitamins is only advised after the second trimester and for certain women who are deficient in specific nutrients in the early stages of pregnancy. Not everybody needs vitamins.

Substances that cause psychosis, sleeping tablets, and tranquilizers can interfere with a child’s developing brain. All substances ingested by the mother can reach the baby’s bloodstream until the baby is fully developed and protected by the placenta. This holds true for bacteria, viruses, and undesirable materials. Miscarriage, frozen pregnancy, and placental pathologies are highly probable.

Recommendations

The primary guidelines for women in the first trimester are fairly straightforward when taking the risks into account.

• Lead a healthy lifestyle, give up alcohol (even non-alcoholic beer), do not smoke, do not take drugs.
• Avoid taking medications without consulting a doctor. When prescribing vitamins, ask how justified this prescription is (ideally, the doctor should conclude about the deficiency of certain vitamins based on the results of a biochemical blood test), in the absence of a vitamin deficiency, refuse vitamin preparations in the first trimester.
• Sleep more. You need at least 8-9 hours to restore the colossal energy costs that accompany the intensive processes in the female body.
• Eat right. It is not necessary to immediately change your diet radically, it will be enough to adjust it a little: start eating 5 times a day in small portions, make sure that the food contains enough carbohydrates, proteins and fats, and not only vegetable proteins, but also animal ones. Vegetables and fruits should appear in the diet, fried, smoked products and dishes, spicy foods, fast food, factory-made sweets and carbonated drinks should leave it.
• Don"t delay with registration – you can do this at any time, but it is best to do it before 12 weeks, this will make it possible to identify possible anomalies and defects of the fetus, pregnancy complications at the earliest stages.
• Try to stay in a good mood and maintain peace of mind. Stress hormones, which are produced in women during periods of stress and negative emotions, have a suppressive effect on sex hormones, which can lead to miscarriage, frozen pregnancy, and fetal developmental abnormalities.
• Avoid contracting viral infections, Do not visit large shopping centers, crowded concerts and performances, try to avoid traveling on public transport during rush hour. This will help protect against the flu, acute respiratory viral infections, chickenpox, measles and other diseases that are dangerous for the development of the baby.

It’s crucial to contact a doctor rather than self-medicate if you start to feel worse during the first trimester. Folk remedies themselves can be dangerous.

Examinations and tests

The most informative examinations are all those conducted during the first third of the gestation period. They let you evaluate perinatal risks fairly and impartially. The day of contacting the consultation will mark the completion of the initial examination. The doctor will create a personalized examination plan for each expectant mother based on her health, number of births and abortions, and personal obstetric history. It will be predicated on the Ministry of Health’s recommendations.

A woman registering will have a long list of tests to complete before 11–13 weeks, in addition to a gynecological exam. This is because this is when the first prenatal screening, which determines the fetus’s risk of chromosomal abnormalities, will occur.

When requesting a consultation, a thorough initial assessment will comprise:

• blood tests for group and Rh factor, coagulogram;
• general blood and urine tests;
• blood test for HIV status, syphilis and infectious hepatitis;
• test for TORCH infections;
• analysis of a smear of vaginal secretions.

Although it’s not required, the initial ultrasound is almost always done even before screening. Its goals are to confirm the existence of uterine pregnancy, define the term, count the fetuses, rule out hydatidiform and ectopic moles, and rule out uterine tumors. A woman gives blood for a biochemical study at 11–13 weeks along with having a screening ultrasound to look for signs of chromosomal abnormalities in the developing foetus.

Further testing is recommended if a high risk is verified.

Second time period

The second trimester, which lasts from 14 to 26 weeks, is thought to be the calmest since the majority of the risks have passed. The child’s already formed organs are growing and developing, and various systems are starting to function. Nothing new is developing in the child. Although the tummy starts to grow, women generally feel good during this time because the placenta is forming, the mother is calm, the child is more protected, toxicosis passes, and carrying the baby is not yet burdensome or difficult.

What happens?

The baby is actively gaining weight even though its growth is slower than it was in the first trimester. When he weighs 500 grams at 22 weeks, childbirth will no longer be regarded as a miscarriage—rather, it will just be considered an early birth. There will be a chance for the baby to live.

The baby’s heart continues to beat unevenly in the second trimester, with the right chambers still beating harder than the left. By the conclusion of the third trimester, things have stabilized. Half of the blood is sent to the brain by the heart, with the remaining half traveling down the aorta.

The infant’s lungs "train" at the start of the second trimester. He does not, of course, breathe in the conventional sense, but his lungs are already moving in the right directions, which is how the respiratory reflex is formed. By the 22nd week, tiny alveolar bubbles start to form. Later, the phospholipid substance known as surfactant, which prevents the baby’s lungs from sticking together after the first inhalation and exhalation, is produced.

The reason that an early birth before the 37th week is risky is that it may result in distress syndrome, which is characterized by respiratory failure, or the inability to breathe, which kills many premature babies.

The baby’s immune system starts to function by the middle of the second trimester. Even though the baby has all the immune cells, their immunity is still very low. The child’s intestinal peristalsis begins at the start of the third trimester of pregnancy, during which time meconium—dark green excrement—is deposited in the intestine and will be expelled after birth.

The kidneys grow very slowly, and only around 36 weeks of pregnancy do their functions finally become fixed. Due to the child’s immature buds and the potential for a fluid and salt imbalance in the body, giving birth during the second trimester is dangerous.

Even in the first trimester, the baby starts to move, but pregnant women don’t feel it until the second trimester—the original ones start to move at 20 to 22 weeks, and the re-resident moves at 18 weeks. Movements take on more significance as the fetus’s nervous system progressively matures. Babies frequently turn their heads up and down, rotate on their axis, and bend and extend their limbs until the end of the trimester.

The brain’s cortex is growing. The vestibular apparatus and motor centers develop, the layers of the brain completely separate by the 27th week, and the brain gains weight and assumes control of the baby’s organs and systems. Adaptation mechanisms and sensory adjustments start in the 26th week.

Risks and dangers

The primary risk factor for the second half of the second trimester is gestosis, a type of late toxicosis that presents as internal, external, and visually discernible edema.

Perinephritis is another risk factor. Apart from providing nourishment and shielding the fetus from harm, the placenta secretes certain hormones that are critical to the developing embryo. Thus, intrauterine growth retardation, fetal hypoxia, and fetal death can result from placental abnormalities. It’s crucial to understand that a deficiency in growth hormones also hinders the development of surfactant in the developing baby’s lungs.

Which second trimester complications are most frequently identified?

• premature birth (survival up to 25 weeks is extremely low, then it grows to 80% by 27 weeks, but the risk of disability in children of survivors remains high);
• ICI (functional insufficiency of the cervix);
• placental pathologies;
• intrauterine fetal infections.

A woman should see a doctor twice a month to ensure that illnesses like gestational pyelonephritis, diabetes, and anemia are identified and treated early.

Colds, the flu, and severe respiratory viral infections are no longer as harmful to the unborn child as they once were. However, because of the potential for high temperatures, they are now dangerous. Because it can cause the placenta to age prematurely and disturb the uteroplacental blood flow, it’s crucial to avoid having a high fever when sick. The use of pharmaceuticals is growing; a woman may be prescribed antibiotics and antipyretics if needed.

Useful tips and recommendations

During the second trimester, a woman must pay close attention to her health.

• Monitor vaginal discharge, using sanitary pads – if bloody, dark, brown or purulent discharge appears, you should immediately contact a doctor.
• Prepare your mammary glands for the upcoming breastfeeding. Wash them with water of a contrasting temperature, rub them lightly with a rough towel – this will help the nipples to become somewhat rougher, which will make it easier to feed the baby later.
• Increase the amount of daily sleep by 1 hour during the day. In total, a woman should sleep at least 9-10 hours a day.
• Choose comfortable clothes taking into account the fact that sweating increases by the middle of the trimester. Wear a supportive bra with wide straps to relieve back pain due to breast enlargement. If necessary, after consulting a doctor, start wearing a prenatal bandage.
• While you still have strength, tidy up the house, start arranging the nursery. Dedicate time to baby shopping, because in the third trimester, going to the shops and cleaning will become much more difficult.
• The diet should be rich in vitamins, it"s time to add multivitamins, saturate the diet with healthy and wholesome food, steamed, boiled and baked. The main thing is to prevent constipation and hemorrhoids.
• A woman should monitor her own weight weekly. An increase in weight above the norm can be not only a consequence of overeating, but also a sign of internal edema with gestosis – be sure to tell the doctor about the increase.

Examinations, tests

A mid-gestation woman must be weighed, have her blood pressure checked, and have her arms and legs checked for edema when she arrives for her consultation. The cervix is measured, examined, and recorded in the exchange card after 20 weeks. The woman has a general urine test performed prior to each doctor’s appointment. If required, all required studies are completed, and new blood tests are performed for syphilis and HIV.

An ultrasound is performed on a woman not only as part of a screening but also whenever the doctor has concerns regarding the mother’s and baby’s health. An ultrasound with Doppler is done during the second trimester; this color ultrasound helps determine the fetus’s blood vessel and heart function as well as the rate of blood flow in the uteroplacental system. If a woman is found to be predisposed to gestosis, medication prophylaxis is administered at weeks 15 and 20 and 21.

The second prenatal screening is performed between 16 and 21 weeks. As part of this screening, the woman again provides blood from a vein for a biochemical study and has an ultrasound to look for fetal abnormalities and malformations.

Trimester	Description
First Trimester	The first three months where the baby"s organs begin to develop, and the mother may experience nausea and fatigue.
Second Trimester	Months four to six, where the baby grows larger, and the mother often feels better and may start feeling the baby move.
Third Trimester	The last three months where the baby gains weight, and the mother prepares for childbirth with more noticeable discomfort.

There are three distinct stages to the amazing journey that is pregnancy, each with its own milestones and difficulties. Expectant mothers and their families go through a period of excitement, anticipation, and sometimes uncertainty as their bodies change and adapt.

New feelings and symptoms may appear during the first trimester as the baby develops. With increased energy and more discernible baby movements, the second trimester frequently brings a sense of relief. Finally, with both physical growth and emotional preparedness reaching their zenith, the third trimester primes the body and mind for the baby’s arrival.

Comprehending the progression of each trimester can enhance the enjoyment and reduce the sense of overwhelm during this unique period. You can navigate pregnancy with confidence and concentrate on the happiness that comes with expecting a new member of the family by remaining informed and paying attention to your body.

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