Pregnancy week by week – The weeks of pregnancy are mainly marked by the development of the baby, which is more sensitive in the first 12 weeks, as it is the phase in which a rapid multiplication of cells and the formation of the main organs occur. However, throughout pregnancy there are also several changes in the woman’s body, which can result in certain symptoms and discomforts such as morning sickness, tiredness or tenderness in the breasts, for example.
Around 12 weeks, the formation of the placenta and the umbilical cord occurs, which will provide the nutrients and oxygen necessary for the maturation of all the baby’s organs, which will continue to develop until the end of the pregnancy, which generally it lasts 9 months on average, or 40 weeks, but can be extended up to 42 weeks.
Pregnancy week by week – Fetal development
1 month – up to 4 weeks gestation
The first month of pregnancy corresponds to the first 4 weeks and the beginning of the first trimester of pregnancy, a phase in which the fertilized egg implants in the uterus, starting the division of the cells of the embryo and stimulating the woman’s body to produce the hormone beta-HCG to create the conditions for the baby to develop inside the womb.
This hormonal increase can cause the first symptoms of pregnancy, such as morning sickness, tiredness or breast tenderness, which can often be confused with symptoms of premenstrual syndrome (PMS).
In this phase of gestation, the placenta is not yet formed, but the baby is surrounded by the gestational sac, which protects from infections or blows and is responsible for forming the placenta and the amniotic sac, being present until approximately 12th week of gestation.
At the end of the first month, the baby is about 2 millimeters in size, and the neural tube that will give rise to the baby’s nervous system and brain is already formed.
2 months – 5 to 8 weeks gestation
At the beginning of the 2nd month, the baby’s heart is formed and begins to beat and pump blood at a fast rate. Until the end of this month, other organs such as the lungs, the liver, the intestine and the kidneys also begin to form, as well as the neurons and the small protuberances that will give rise to the arms and legs.
Although the fetus is still very small, measuring around 13 millimeters at the end of the 2nd month, it is at this stage that most women discover that they are pregnant.
In this month of pregnancy, it is common for women to have symptoms of discomfort and morning sickness that usually last until the end of the 3rd month of pregnancy, which are caused by rapid hormonal changes. Some tips to improve these symptoms may be to avoid strong odors and intense foods, not to fast for a long time and rest, as tiredness tends to worsen nausea.
At the end of the 2nd month, it is possible to find out the sex of the baby through fetal sex screening, which is done by analyzing a sample of the mother’s blood.
3 months – 9 to 13 weeks gestation
The 3rd month of pregnancy corresponds to weeks 9 and 13 of gestation, and also to the end of the first trimester. This month of pregnancy is marked by the formation of bones and cartilage, of the auditory canals, nostrils and elbows, so it is already possible for the baby to flex his arms. Likewise, the baby’s organs are already formed and beginning to function, but they continue to develop and mature until the end of the pregnancy. Also, the ovaries or testicles are also already fully formed.
By the end of the 3rd month , the baby is about 7.4 centimeters long and the placenta is fully formed. The woman’s belly begins to show, morning sickness is usually not as frequent and the breasts begin to become more and more voluminous, which increases the risk of stretch marks.
4 months – 14 to 17 weeks gestation
The 4th month corresponds to the beginning of the 2nd trimester of pregnancy, and in this month the baby begins to swallow amniotic fluid and develop sucking and swallowing reflexes for future breastfeeding. Also, the lungs are developing and the baby is already able to make respiratory movements, inhaling the amniotic fluid.
The baby’s skin is thin and covered by lanugo, a thin layer of hair that helps regulate body temperature, and despite the fact that the eyelids are closed, the baby is already able to move his eyes from side to side and notice the difference between light and dark.
At the end of the 4th month, the baby measures about 13.5 centimeters, measured from head to toe, and weighs about 179 grams. The woman’s belly is already noticeable and her waist takes on a more rounded appearance.
5 months – 18 to 22 weeks gestation
The 5th month of pregnancy corresponds to weeks 18 and 22 of gestation, and the baby already has well-formed ears, managing to hear the mother’s heartbeat. Likewise, the uterine tubes are already positioned in the correct place, if she is a girl, being possible to confirm the sex of the baby through a morphological ultrasound.
In this phase of pregnancy, the formation of vernix caseosa also takes place, a kind of white covering on the skin, which serves as protection and hydration of the skin, as well as preventing infections and regulating the temperature of the baby’s body.
At the end of the 5th month of pregnancy, the baby measures about 27.4 centimeters, weighs about 476 grams, and its movements can already be felt by the woman. The pregnant woman could present a darker line known as the linea nigra , which runs from the navel to the genital region and is normal and occurs due to hormonal changes during pregnancy, in addition to Braxton-Hicks contractions, which are mild and are considered normal.
6 months – 23 to 27 weeks gestation
The 6th month of pregnancy corresponds to weeks 23 and 27 and marks the end of the second trimester of pregnancy. In this month, the baby begins to open his eyes, already has a sleep routine and has a more developed sense of taste. Hearing is becoming more precise and the baby can already perceive external stimuli, responding to touch or being startled by loud noises.
At the end of this month, the baby measures about 34.7 centimeters, measured from head to toe, and weighs about 1.03 kg. The woman will be able to more easily notice the movements of the baby, which is why stroking the belly and talking to him can calm him down.
7 months – 28 to 31 weeks gestation
The 7th month of pregnancy corresponds to weeks 28 and 31 and marks the beginning of the third trimester of pregnancy. In this phase, the baby’s head is already larger and the brain is developing and expanding, so its nutritional requirements are increasing. The baby moves more lively, recognizes the mother’s voice and reacts to sounds and lights.
By the end of the 7th month, the baby is about 16 inches long and weighs about 4 pounds; also, the woman may feel pain in the back and pelvic pain due to constipation.
In this phase, it is already important to start buying the necessary items for the baby, such as clothes and a crib, and to prepare the suitcase that is going to be taken to the maternity hospital.
8 months – 32 to 35 weeks gestation
The 8th month of pregnancy corresponds to weeks 32 and 35 of gestation, and at this stage the baby’s lungs are already more developed, although they continue to mature until the end of gestation. However, they already produce pulmonary surfactant, a substance that will contribute to the exchange of oxygen during respiration after birth.
At the end of the 8th month of pregnancy, the baby is about 18 inches long and weighs about 5 pounds. At this stage, the head is beginning to move from side to side, the digestive system is already properly formed and the bones are becoming stronger, but at this time the baby has less room to move.
For women, this phase can be uncomfortable, as the legs swell and varicose veins can appear or worsen, so walking 20 minutes in the morning and resting during the day can help.
9 months – 36 to 42 weeks gestation
The 9th month of pregnancy corresponds to weeks 36 and 40, but can extend up to 42 weeks. At this stage of pregnancy, the baby continues to grow and gain weight, the skin is thinner and smoother, and the lanugo begins to disappear.
Until the 37th week, most babies are already in the proper position for birth, that is, turned head down. However, certain babies may take a little longer to turn, which should be evaluated by your obstetrician until late in pregnancy.
At the end of the 40th week of pregnancy, the baby is about 51.2 centimeters and weighs about 3.5 kg, and the birth at this time is considered full term. However, it is possible for the baby to be born up to 41 weeks and 6 days, being called late term, or up to 42 weeks, being considered post-term.
If labor does not start spontaneously until 41 weeks and 3 days, the obstetrician may choose to induce labor, which involves administering oxytocin into the mother’s bloodstream in the hospital to stimulate the uterine contractions, or perform a cesarean section.