Pregnancy is divided into three trimesters. Each of them lasts between 12 and 13 weeks. During each trimester, the baby develops, and changes take place in the pregnant woman’s body. Pregnancies normally last about 40 weeks. They are counted from the first day of the woman’s last menstrual period, which is two weeks before fertilisation actually happens.
Before the stages of pregnancy can begin, fertilisation needs to happen. Fertilisation happens when a man and a woman have sex and the man’s sperm meets a woman’s egg. At fertilisation, the sex of the baby is already determined. The sex depends on which chromosome the sperm was carrying. Chromosomes are part of the genetic material that both the mother and the father pass on to the baby. If the egg receives an X chromosome from the sperm, the baby will be a girl. If the egg receives a Y chromosome, the baby will be a boy.
FIRST TRIMESTER (WEEKS 1 TO 12) – CHANGES IN THE MOTHER
During the first trimester, the pregnancy may not be showing outside of the woman’s body yet, but inside many changes are taking place. For example, important hormones in the female reproductive system like oestrogen and hCG rise in concentration. These may be responsible for the waves of nausea and vomiting that many women feel during the first few months of pregnancy. Women also feel more tired during the first trimester, their breasts feel more tender and they often need to urinate more. Many parts of the woman’s body have to work harder during the pregnancy. This includes the heart, which needs to circulate enough blood to supply both the mother and the baby.
FIRST TRIMESTER (WEEKS 1 TO 12) – CHANGES IN THE BABY
The baby also changes a lot during the first three months. During the first month, its heart and lungs begin to develop, and the arms, legs, brain, spinal cord and nerves begin to form. By the end of the first month, it will be around the size of a pea. In the second month, the ankles, wrists, fingers and eyelids form, bones appear, and the genitals and inner ear begin to develop. By the end of the second month, the baby has grown to the size of a kidney bean. During the third month, bones and muscles begin to grow. The intestines also begin to form. At this point, the baby is about 7-10cm long or the length of a finger.
SECOND TRIMESTER (WEEKS 13-27) – CHANGES IN THE MOTHER
By the second trimester, a baby bump starts to appear. The size of the bump depends on how the baby is positioned inside the woman’s body and her own body structure. Some of the side effects of pregnancy may become less intense as the woman’s body adjusts to the changing hormone levels. For many women, sleeping becomes easier, they have more energy again and they feel less nausea. At the same time, other symptoms like more pelvic pressure and back pain may start to appear. It is during this trimester that the mother can start feeling the baby move around.
SECOND TRIMESTER (WEEKS 13-27) – CHANGES IN THE BABY
The baby grows a lot during the second trimester. By the fourth month of pregnancy, eyelashes, fingernails and the neck start to form. The kidneys start working and the baby can swallow and hear. By the fifth month, the baby sleeps and wakes up on regular cycles and becomes more active in its movements. In the sixth month, its hair begins to grow, the eyes begin to open, and the brain is rapidly developing.
THIRD TRIMESTER (WEEKS 28-40) – CHANGES IN THE MOTHER
In the last trimester, the baby becomes so big that it pushes against the muscles involved in the mother’s breathing. This makes many women feel short of breath. Their ankles, hands, feet and face often swell because they retain more fluid and blood circulation slows down. Because the baby is also putting more pressure on the mother’s bladder, she will need to pee more often. Her backaches may start to become worse as her hips and pelvis start to relax in preparation for the delivery of the baby. A lot of women’s faces start to develop dark patches of skin, stretch marks appear on their bellies, thighs and breasts. The woman’s breasts may leak some yellow liquid. This is called the colostrum and will be the first thing the baby eats. Some women also experience a ‘false labour’, contractions which last for a short time but then go away again. The baby is so big at this point that a lot of women have trouble finding a comfortable position to sleep in.
THIRD TRIMESTER (WEEKS 28-40) – CHANGES IN THE BABY
By the seventh month of pregnancy, the baby can kick and stretch. It can also respond to light and sounds. It can open and close its eyes. During the last months, the baby gains a lot of weight and the bones harden. In the last month of pregnancy, the baby gets ready for the birth by turning into a head-down position inside the woman’s belly.
After 39 to 40 weeks of pregnancy, the baby is born.