Pregnancy can be an exhilarating journey, even though a woman might not feel her best for the entire duration of it. The process is not just different for each woman, but it is also different for the same woman from one pregnancy to the next. Symptoms of pregnancy vary throughout the trimesters and are usually visible after the first 4 weeks.

Conception and implantation
Between the 6th and 14th day of the menstrual cycle, follicles in one of the ovaries begin to mature. After the 14th day, a sudden surge in luteinizing hormone causes the ovary to release its egg. The egg travels from the fallopian tube to the uterus over a course of five days. 

If this mature egg comes in contact with a sperm that has made its way to the fallopian tube, they combine into one cell. This process is called fertilization. The fertilized egg travels to the uterus for further growth and development, which is known as implantation. 

Pregnancy is divided into three trimesters. Each trimester lasts for 12–13 weeks. Several changes take place in a pregnant woman’s body as well as in the developing baby in the womb during each trimester. 

First trimester
It lasts between 1–12 weeks and includes symptoms and changes such as the ones mentioned below.
A woman’s body goes through multiple changes in the first trimester as it adjusts to the hormones released. While there may not be any major changes visible, it does not mean nothing is happening. A pregnant woman may feel more tired than usual during the first trimester. This symptom is linked with a rise in the level of progesterone hormone which increases sleepiness. The need to urinate may also be more frequent as the uterus grows and presses against the bladder. 

The breasts might feel more tender and swollen, which is another sign of rising levels of the hormones. Changing hormone levels also slow down the digestive system. The reduced metabolism then leads to other symptoms such as constipation, heartburn, bloating and acidity.

Second trimester
The second trimester begins from the 13th week and lasts for 13–14 weeks. This period is believed to be the most relaxed one and comprises changes as given below. 

By the beginning of the second trimester, most of the unpleasant effects of pregnancy experienced in the first trimester tend to lessen. The body adjusts to its changing hormone levels leading to the possibility of improved energy levels and better sleep.

Things like morning sickness may stop being an issue too. However, other symptoms might begin to appear as the pregnancy progresses. Pregnant women in their second trimester might feel more pressure on their pelvis. As the uterus exerts more pressure and the pelvic floor weakens, it may become heavier and feel fuller.  A more visible baby bump appears as the uterus expands and the skin over this area might itch as it stretches. Expectant mothers may also face backaches due to the weight gained during pregnancy. 

Somewhere between 16th and 18th weeks of pregnancy, a woman may feel first fluttering movements of the baby known as quickening. It is also during this period that the baby starts moving around more in the womb. The 20th week usually marks the halfway point of the pregnancy. 

Third trimester
The third trimester is the final stage in pregnancy before a woman delivers the baby. It begins from the 28th week and lasts for 12 weeks.

The uterus is now enlarged and can push against the diaphragm (the major muscle involved in breathing). As a result, the expectant mother may fall short of breath due to the lungs having less room to expand. Additionally, slower blood circulation in the body may result in swelling in the feet and ankles due to fluid retention. 

Women in their third trimester of pregnancy also experience the frequent urge to urinate as there is increased pressure on the bladder. Backaches and pelvis and hip pain might also be experienced during this time. Aside from these, symptoms like dark patches on the skin, stretch marks on the belly, breasts, and thighs, and even varicose veins on the leg are not uncommon.  Another change observed is that while the breasts start feeling tender in the first trimester itself, they might leak a watery pre-milk liquid called colostrum. This is secreted in the first 2–3 days after delivery. The to-be mother may experience Braxton-Hicks contractions which are also called false labor as she gets closer to her due date. 

As a pregnant woman nears the due date, the cervix will become thinner and softer. This process is called effacing and it helps the birth canal to open during the birth process. The doctor will check for the same after the 39th week.