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An Adventure Called Pregnancy (Part 1) - A Look Into the First Trimester of the 40 Weeks Journey

Updated on February 4, 2017
Fetus in First Trimester
Fetus in First Trimester | Source

What is First Trimester of Pregnancy

Pregnancy is measured in trimester. There are three trimesters in pregnancy. Pregnancy is measured from the first day of the last menstrual period and not from the day the baby is conceived. Conception actually occurs about two weeks after the last period begins. If someone is four weeks pregnant, then it is two weeks after the conception. Thus, in a 40 weeks pregnancy, the fetus is actually 38 weeks old.

The first trimester of pregnancy is from week 1 through week 12. In the very first weeks the developing baby is called an embryo and from eight weeks onward it is called a fetus.

During these 12 weeks lot of transformations take place in the mother's body due to the trigger of hormones. This helps prepare the body to nourish the baby even before the tests can confirm a pregnancy.

Weeks 1 & 2

You have not yet conceived. You should start taking prenatal multivitamins with folic acid daily. In fact the regimen should be started three months before one starts trying to get pregnant. The egg starts maturing about three months before it is released. It is thus essential that the necessary nutrients are present during the earliest stages.

Menstrual cycle has just started. If a woman has 28 day cycle then ovulation occurs around 14 days after the start of the menstrual cycle. If a woman has a menstrual cycle longer than 28 days or irregular, the day of conception can be any time after the 14th day. In such cases it is difficult confirm exact dates in the early stages of pregnancy.

Lining of the uterus is shed through menstruation at the end of week 1. At the 2nd week a fresh bed of blood rich tissues are now forming to welcome the fetus. Eggs are ripening in the ovaries to be released and fertilized.

In-vitro Fertilization of Human Egg. Several Sperms are Trying to Penetrate
In-vitro Fertilization of Human Egg. Several Sperms are Trying to Penetrate | Source
The Embryo at Week 4 is the Size of a Poppy Seed
The Embryo at Week 4 is the Size of a Poppy Seed | Source

Weeks 3 & 4


Several sperms meet the egg in the fallopian tube. Although all of them try to penetrate the egg's outer layer, only one will successfully enter the egg and fertilize it.

Chromosome from each parent combine to create a cell which then starts dividing and becomes a collection of cells or blastocyst. While moving down the fallopian tube the blastocyst continues to divide and grow. Once it reaches the uterus 3 to 7 days later, it implants itself to the lining of the uterus. Blastocyst draws in liquid creating a liquid pocket in the center. This fluid space creates a division in the blastocyst, giving rise to a inner cell mass, which ultimately becomes an embryo, and an outer tophoblast, which will form the placenta.

When the blastocyst implants in the uterus it is about 0.23 mm or 0.009 inches long.

Multiple Pregnancies

Fraternal twins are conceived if two eggs are released from the ovary or one egg from each ovary and are fertilized by two sperms. They may or may not have the same sex and usually look different.

Identical twins are borne if one egg is fertilized and later splits into two. In such cases both children have the same sex.

Maternal Changes

When blastocyst implants into the uterus some spotting or mild bleeding may occur. It's normal and there is nothing to worry about. But not all women experience it.

A home pregnancy test at 4th week may produce a false negative result.

Am I Pregnant

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Stages of Fertilization of a Ovum
Stages of Fertilization of a Ovum | Source
Embryo at 5th week
Embryo at 5th week | Source

Week 5

Fetal Changes

The blastocyst, which was the growing baby, is now called an embryo. Inner cell mass has flattened to form the embryonic disc and the body stalk.

Embryonic cell divides further into 3 basic germ layers - ectoderm, mesoderm and endoderm. The ectoderm or the outer layer develops into the nervous system, brain, spinal cord, skin and hair, eyes and ears.

The mesoderm or the middle layer forms the supporting structure like bones, joints, muscles, connective tissues, heart, kidney, circulatory system, genital and urinary systems. The circulatory system is the first system to function.

The endoderm or the inner layer grows into gastrointestinal tract including liver, pancreas, gall bladder and the lungs.

Embryo is encased in a protective membrane and is attached to a yolk sac, which manufactures the embryo's unique blood cell.

In the beginning of 5th week spinal cord and brain start to develop. During this time the embryo is about 0.05 inches long.

Maternal Changes

This is the time a woman misses her period. Home pregnancy tests measures the level of pregnancy hormone hCG in the urine. If tested a few days after missing the period, a positive result is likely to be obtained.

The hormonal changes also brings about some other changes in the body. Breasts are now swollen and tender as milk glands multiply. There are frequent hunger pangs and morning sickness kicks in. Urination is more frequent as the growing uterus puts pressure on the bladder.

What Should an Expectant Mother Do at 5th Week

1. Visit the doctor to confirm pregnancy.

2. Eat healthy and balanced diet.

3. Reduce caffeine consumption and stop taking alcohol.

4. Do moderate exercise. Consult an expert to know the kind of exercises that are suitable for you.

5. Don't take any kind of medicines without consulting your doctor first.

First Trimester of Fetal Development

Embryo at 6th Week
Embryo at 6th Week | Source

Week 6

Fetal Changes

The embryo is about 0.08 - 0.16 inches long. Yolk sac and amniotic sac develop at this time. Amniotic sac continues to grow and gradually envelops the embryo. The yolk sac disappears once the embryo is capable of obtaining nourishment from the placenta.

The body stalk connecting the embryo to the developing placenta or trophoblast elongates gradually and becomes umbilical cord. It contains two arteries and a vein.

A bulge forms where the embryonic heart is and a bump forms where the head is. This is the time the pin-sized heart starts beating and the brain starts developing. The heart beat at this stage is about 150 beats per minute.

There is an over-sized head where facial features are forming. Dark spots form where eyes will develop, openings where there will be nostrils and pits where ears will form. Protruding buds that will become arms are leg are already visible.

Maternal Changes

Feeling of nausea, heartburn and morning sickness are common during this period. There are cravings for certain foods while the other foods are found to be repelling. Breast tenderness, fatigue and frequent urination are other common symptoms during this period. A woman may also experience frequent mood swings.

Some Cautions

The possibility of miscarriage is always there. Doctor should be immediately consulted if there is

1. Bleeding.

2. Pain in lower abdomen

3. Passing of grayish or pinkish tissue or blood clots with urine.

Not all bleeding are signs of miscarriage though. Many women have bleeding during pregnancy, yet they have healthy baby. I had bleeding till 7th month of pregnancy, when I was pregnant with my daughter.

Embryo at Week 7
Embryo at Week 7 | Source

Week 7

Fetal Changes

The baby is now about 0.33 inches long. It has now distinct but webbed fingers and toes. Fetus during this time jumps around a lot. The liver produces a huge amount of red blood cells till the bone marrow forms and takes over this role. The lens of the eyes form, and so do the nostrils, intestines, pancreas and bronchi.

The brain begins to form. Different portions of the brain continue to grow, causing the head to be pushed forward and make it rounder. The valves of the heart begin to develop at this stage.

Maternal Changes

Though there is no outward change in appearance, some internal changes due to the release of hormones.

  1. Increased vaginal discharge - This is common. But if there is any irritation, soreness or bad odor, consult your doctor immediately.
  2. Tiredness - One should try to get as much rest as possible.
  3. Tenderness of breast - Another early symptom of pregnancy that occurs due to the increased blood supply. For some women, the breasts become hard.
  4. Morning sickness - Though it's called morning sickness, the feeling of nausea and vomiting can occur at any time of the day. This may continue till 12th to 15th week. Morning sickness can be managed by eating small and frequent meals and avoiding oily food. Never let the stomach be completely full or completely empty. Taking ginger tea or sucking a slice of lemon can help. Medications can also be taken to alleviate the symptom.
  5. Constipation - Occurs during early pregnancy and may continue well after the child is born. Drinking plenty of water, eating lots of fruits and vegetables may ease the problem.
  6. Muscle cramps - Caused by the stretching of the muscle. It usually worsens at night. You should sit up and pull the toes towards the body over the ankles.
  7. Itching - Occurs due to the stretching of the skins. Itching notions like Calamine can be soothing.
  8. Frequent urination - It is caused by the pressure of the enlarging uterus on the bladder.

How To Fight Food Aversion and Nausea

Don't miss meals.

Eat small snacks.

Avoid large drinks. Take small frequent drinks between meals.

Avoid spicy foods.

Avoid excessive salt.

Take lemon or orange juice in the morning and before meals to relieve nausea.

Suck an ice cube till the nausea passes off.

Sip on cool water.

Pelvic Rotation Exercise

Pelvic Exercises

Pregnancy Yoga

Fetus at eighth week of pregnancy
Fetus at eighth week of pregnancy | Source

Week 8

Fetal Changes

The embryo which is now a fetus is about 0.7 inches long. Embryonic tail has disappeared. Heartbeat can be heard during ultra sound. Elbow started to form and finger began to appear. Baby's hand now bends at the wrist. Legs too started to form and tiny notches for toes are visible.

The facial features are beginning to take shape. as forehead, nose, cheeks, upper and lower jaw and tip of the chin started forming. Eyelids and muscles have formed too. Nasal passage forms by the end of the 8th week. Ear openings are there but the hearing is not possible at this stage.

Nerve cells are branching out in the brain to connect to one another, giving rise to primitive neural pathways.

Maternal Changes

Uterus is now the size of an orange and the waistline is expanding. Some women crave at this stage for all kinds of weird foods and drinks. It is also good time to start pelvic floor exercises. They are needed to strengthen the muscles of the vaginal wall so that it will be easier to push the baby out during delivery.

During pregnancy pelvic muscles come under immense strain due to the weight of the growing baby. This may lead to urine incontinence. In more serious cases, a weak pelvic floor may also lead to pelvic organ prolapse, i.e. the bladder may drop from its usual position and push against the vagina.

Fetus at 9th week
Fetus at 9th week | Source

Week 9

Fetal Changes

By the end of 9th week the baby is about 0.9 inches long and it's weight is less than 2 g. Basic structure of the eye is well under way. Eye lids completely cover the eyes and remain fused together till about 26 weeks. External ears are tiny and become visible. Tongue also develops at this stage.

The intestine starts to move out of the umbilical cord and into the abdomen of the fetus. Neck is more defined and developed, allowing the lifting and turning of the head. The fetus more or less looks like a tiny human being now. His wrists are more developed, ankles have formed, fingers and toes are clearly visible. arms have grown longer and bend at the elbows.

Though the sex of the baby cannot yet be told yet, but the genitals have begun to form. Placenta is well developed and is producing the essential hormones. The placenta is also making nutrients for the baby and getting rid of the waste products.

Maternal Changes

Uterus is now the size of a grapefruit. Blood volume increased by about 40% - 50% to serve the needs of the expanding uterus. A cramping sensation is felt in the lower abdomen due to the growth of the uterus. But if there is bleeding along with pain, one should consult a doctor. The uterus grows and contracts during pregnancy and during later stages, these are called 'braxton hicks' contractions.

Human chorionic gonadotrophin (hCG) hormones are present during the first trimester of pregnancy and is the main cause of nausea and vomiting.

Estrogen stimulates the growth of blood vessels, glands, muscle cells of the uterus and the breast tissues.

Progesterone is another important hormone that provides nutrients and stimulates the formation of ducts in the breasts. It also acts as the feedback hormone that tells the hormone-producing center in the brain to stop producing hormones related to menstruation.

Fetus at week 10
Fetus at week 10 | Source

Week 10

Fetal Changes

The baby is now about 1.22 inches long and weighs about 5 g. All the major organs and the facial features have almost formed. Though so little, the baby is very active as it swallows fluids and kicks about its tiny limbs. From this point onward the baby starts growing and gaining weight rapidly. But the mother won't feel it yet.

The head is half the size of the entire body and the forehead is bulging. Fuzzy hairs become visible. Outline of the spine is clear. Spinal nerves stretch out from the spinal cord.

Maternal Changes

Uterus is the size of a grape fruit now. Morning sickness begins to abate from this week onward. Mood swings take place due to the hormonal changes. First ultrasonography is done at this stage.

Some blood tests prescribed by the doctors during this time are:

  • hemoglobin and platelet levels.
  • blood group and rhesus status.
  • rubella.
  • hepatitis B.
  • HIV.
  • thalassaemia.
  • sickle cell anemia.

Some common urine tests that might be recommended are:

Ketones - are excreted by the body if one is not eating enough nutrients. It also indicates the development of gestational diabetes.

Glucose - may be a sign of diabetes or kidney disease.

Protein - may be a sign of infection, but it may also mean hypertensive problems in pregnancy such as pre-eclampsia.

Modern testing facilities enable us to detect abnormalities in those women who are considered to be in high risk categories. Early detection of abnormalities give an opportunity to decide whether to carry on with the pregnancy. Some such tests which are performed at 10 - 12 weeks of pregnancy are given in the table below.

Some Special Tests

Name of the test
What is tested
What does it detect
Nuchal fold screening
Ultrasound screening to detect specific abnormalities of the fetus
Down's Syndrome
Rhesus factor
If the mother has negative Rhesus then extra blood tests are required
Checks the possibility of anti-body formation
Chronic Villus Sampling (CVS)
Performed between 10-12 weeks of pregnancy to test for genetic or chromosomal abnormalities. The test is performed by inserting a tube through the vagina into the uterus or a needle through the abdomen into the uterus. Some chorionic tissue that surround the fetus are removed by suction for testing
Down's syndrome, sickle-cell anemia, thalassaemia, cystic fibrosis
Though these tests may not be needed or may not be compulsory, it is a good idea to perform them for the sake of being aware of the associated risks. Doctors may recommend them if some abnormalities are suspected.

Weight Gain Chart

Pre-pregnancy Weight
Acceptable Weight Gain in Kg
14 - 18
Normal weight
11 - 16
7 - 11
The amount of weight gained varies from person to person and from pregnancy to pregnancy in each woman. baby - 3.4 kg, uterus - 0.9 kg, placenta - 0.68 kg, breasts - 0.9 kg, blood & fluid - 3.6 kg, fat - 3.2 kg
Fetus at week 11
Fetus at week 11 | Source

Week 11

Fetal Changes

Most critical developments of the baby are over. From now onward the fetus grows rapidly. It now weighs about 7 g and measures approximately 1.6 inches from crown to rump. This is a period of rapid growth.

The head is still half the length of the entire body. A baby boy will start producing testosterone from this week, and both sexes will now have fast developing genitals. The lungs are still very immature, but the heart has divided into right and left chambers and has developed valves and ventricles. Ribs are visible under the still translucent skin. Fetus can now suck, swallow and process the ingested liquid. Baby is also able to kick, punch, flex its fingers, form a fist and arch the body.

Maternal Changes

Uterus can now be felt above the pubic bone. Appetite is better and nausea has subsided, but certain smells may bother the expectant mother.

Bloating is a common problem at this stage, so are acidity and hear burn. This is because the hormone progesterone relaxes smooth muscle tissues in the body, including gastrointestinal tract. As a result the digestion process is slowed down and allows more time for the nutrients from the food to be absorbed in the blood stream and passed to the fetus.

Avoid catching colds. The more colds the mother catches now, it is more likely the child will develop asthma in later life.

Fetus at week 12
Fetus at week 12 | Source

Week 12

Fetal Changes

The fetus now weighs about 14 g and the the crown to rump length is 2.3 inches. Fingers and toes have separated and nails began to form. The skeletal system which began developing earlier, now has centers of bone formation (ossification) in most bones.

Amniotic fluid begins to accumulate as the baby's kidneys begin to produce and excrete urine. The muscles in the intestinal walls begin to practice peristalsis - contractions within the intestines that digest food.

The most dramatic development this week is reflexes. Baby's fingers will open and close, toes will curl, eye muscles will clench, and mouth will make sucking movements. If you prod your abdomen, the baby will squirm in response, although you won't be able to feel it.

Meanwhile, nerve cells are multiplying rapidly, and in the baby's brain, synapses are forming too. Eyes have moved from the sides to the front of the head, and ears are right where they should be.

Maternal Changes

Uterus will shift upward as it grows, thus putting less pressure on the bladder. Some of the problems still experienced are dizziness, change in sex drive, fatigue, excessive salivation, bloating, heightened sense of smell, increased vaginal discharge, occasional headaches.

Risk of Miscarriage

Majority of miscarriages occur very early on, even before the pregnancy can be detected.

By 6 weeks the risk has fallen to 15%.

By 8 weeks the chance of miscarriage is only 3%.

After 12 weeks the chance of miscarriage is no more than 1%.


The first trimester of week-by-week pregnancy is a difficult time. It is a stage when one is not confirmed about the awaited pregnancy but is also an extremely complicated phase when the chances of pregnancy risks are maximum.

I have provided a brief synopsis of fetal development and the maternal changes in the first trimester of pregnancy. I also outlined the common symptoms women experience during this period.

Worst Week In First Trimester

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Spotting In Pregnancy

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© 2016 Sahana

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