Each of the stages of pregnancy, known as trimesters, has its own unique characteristics. The first trimester is defined as the period from the date of conception through week 12. The second trimester lasts from week 12 through week 24 and the third trimester is week 24 to the moment the child is born.
First trimester of pregnancy (from the date of conception to week 12)
Due to the new demands of fetal development, the body of a pregnant woman undergoes complicated protective and adaptive changes. The central nervous system and endocrine glands perform regulatory functions controlling the reorganization of body.
After implantation of the embryo into the endometrial lining of the uterus, the woman’s body starts producing the sex hormone progesterone. It has an immediate influence on the development of the embryo and changes in the mother’s body. The ovaries continue to produce progesterone for about 9 or 10 weeks and after that time, the fetoplacental system (adrenal cortex and liver of the pregnant woman and the fetus) takes responsibility for hormonal function.
There are two developmental stages: embryonic period (first 8 weeks of pregnancy) and fetal period (from the 9th week to the birth). During the embryonic period, the formation of various types of tissues occurs. The fetal period is characterized by the growth of the baby, and the development of its organs and functional systems.
Under the influence of progesterone, breasts tend to enlarge; nipples uplift and the skin surrounding them (areola) become darker and wider. Progesterone can also cause constipation, as it causes relaxation of smooth intestinal muscles, and therefore decreases the strength and the frequency of bowel contractions. It is advisable to drink plenty of fluids in order to prevent constipation.
Often, in the first weeks of pregnancy women suffer from queasiness and nausea which are triggered by the hormonal changes the body undergoes. These discomforts usually go away as the pregnancy proceeds. However, sometimes they continue during all the stages of pregnancy.
Fatigue is common during this period, but this feeling will subside by the second trimester. It is related to the changes in body and energy drain. The real cure for the first trimester fatigue is to sleep 9 or 10 hours every night.
During the first trimester, miscarriage and ectopic pregnancy are possible.
Ectopic pregnancy is a complication where the fertilized egg implants outside the uterine cavity, usually in the fallopian tubes. The growth of the embryo here may result in the major internal hemorrhage and is the reason why an ectopic pregnancy is a potential medical emergency requiring surgery.
Another complication of pregnancy in the first trimester is if the fetal heartbeat stops. In this case the pregnancy will not continue. Dilation (or dilatation) and curettage is performed with laboratory examination to follow.
Second trimester of pregnancy (from week 12 to week 24)
The hormones of the fetoplacental system are responsible for many of the physiological changes in the in the woman’s body. They regulate water-salt metabolism (the retention of sodium at the same time can lead to swelling or edema), increase the volume of circulating blood and stimulate the growth of the uterus and breasts.
Due to lower levels of progesterone, queasiness and nausea subside. In the middle of the second trimester, a woman experiences the first feelings of fetal movement. The breasts may start producing yellowish fluid – the first milk, called colostrum. As the growing uterus presses on the intestines, constipation may become more common and heartburn may occur.
During the second trimester of pregnancy, the baby’s organs are forming and changes in the woman’s body continue. Complications of this period are the following: late miscarriage, bleedings (the usual reason is the presentation of placenta), iron-deficiency anemia, and oxygen starvation (hypoxia) of the fetus. It is very important for the fetus to get enough oxygen in the second trimester, because this period is characterized by the intensive development of the brain. A lack of oxygen can quickly begin to take its toll: the movements of the fetus change, and the fetal heart rate is affected.
During the third trimester the uterus is actively growing, fetal movements are increasing, and labor pains may sometimes occur. They should only last for several minutes and stop after the body position changes. These labor pains push the fetus towards the maternal passages. That is why there is no reason to be scared. However, in the case of frequent labor pains (several times per hour) it is important to consult a doctor.
The increased pressure of the uterus on the urinary bladder may cause frequent urination. As the expanding uterus pushes the diaphragm, and the baby requires enough oxygen, the woman may feel shortness of breath. The pregnant woman may feel tired and suffer from sleeping problems. The reason for it is increasing physical and emotional stress.
Some kinds of malformation and swellings can be detected during the third trimester. Often, the general condition of the pregnant woman (late pregnancy toxemia, for example) can trigger blood flow problems in the uterine vessels, as well as placental and umbilical vessels. These changes can be the cause of abnormalities of fetal growth and development, and oxygen starvation.
An incorrect positioning of the fetus can also be revealed during this period and it is vital to detect any abnormalities beforehand as it defines the steps to be taken during the birth process.
All pregnant women should regularly consult their obstetrician-gynecologist, who will be able to detect and explain all changes over the course of pregnancy.
