The first trimester of pregnancy is calculated from the first day of your last menstrual period up to the end of week 12. This means that during the first two weeks, you are actually not pregnant; your body is simply preparing for pregnancy. From the first day of your last menses, it takes about 2 weeks for the ovaries (ovarian follicles) to release an ovum (mature egg) into the fallopian tubes where the egg awaits fertilization by the sperm. Well, the period when the ovum is released could vary based on your cycle. So, conception takes place, you can now start celebrating as you will soon become a mother to a bouncing baby boy/girl. Your expected date of delivery is expected to be about 40 weeks from your first day of your last menses. So, what exactly happens in each week throughout the period you are pregnant? Let’s discuss that in detail:
Week 1: During the first week of pregnancy (remember you are not really pregnant), your reproductive system is in preparation for ovulation. The ovum starts to leave the ovary towards the fallopian tubes in readiness for the fertilization process. During this time, you are advised to start adjusting your diet by mainly taking folic acid supplements to increase your chances of conception. These supplements protect your unborn baby against spinal bifida. Symptoms such as mood swings, fatigue, morning sickness, and breast tenderness are common during this period. However, these changes are not universal and may not occur until the second week of your cycle.
Week 2: Now your body is preparing for the ovulation process. Your uterine wall starts to thicken, and you experience various pre-menstrual symptoms. Such signs include pain from one side of the uterus, mild cramping, breast soreness and other hormonal changes. If fertilization occurs, you cease to experience menstruation for the next 38 weeks or so. When the egg leaves the ovarian follicle, the follicle then develops what is usually referred to as the corpus luteum, which in turn releases a hormone that triggers the thickening of the lining of the uterus. The egg only survives within the fallopian tube for about 24 hours after which it moves to the uterus. If it isn’t fertilized, it disintegrates but if it is fertilized, it moves to the uterus for implantation to take place.
Week 3: After the fusion of the sperm and mature egg within the fallopian tube, fertilization process is said to have taken place. Your baby’s genes, and gender are determined at fertilization; if the sperm was carrying X chromosomes, your baby will be a girl but if it was carrying a Y chromosome, you will have a baby boy. Technically, you are not pregnant until implantation takes place even if fertilization has taken place. The fertilized ovum now moves from your fallopian tube towards the uterus for the implantation process; implantation is the attachment of the fertilized ovum (zygote) into the walls of your uterus. Initially, the egg is a single cell that then undergoes cell division to form many cells. At first, it divides into 2 identical cells referred to as blastomere, which then multiply again every 12-20 hours as it travels through the fallopian tube to get to the uterus to form a morula at a time when it has 16 cells. A few days later, the morula develops a cavity at the center with cells referred to as blastocyst. At this time, it has 46 chromosomes-23 from the mother and 23 from the father. After around five to seven days since fertilization, the blastocyst attaches to the walls of the uterus (endometrium) in what is known as implantation. At this time, different implantation connections will start forming between the mother and the embryo (the umbilical cord starts forming at this stage). You are now pregnant; congratulation! You may notice some implantation spotting (slight bleeding) about 1 or 2 days after the time of implantation. As such, implantation bleeding is an early sign of pregnancy although not everyone has it. At this time, the lining of your uterus thickens while the cervix is sealed by mucus, which stays in place until you are ready for delivery.
Week 4: You may need to visit a health center in order to confirm your pregnancy, though you may experience pregnancy-related symptoms like the implantation spotting mentioned in week 3. You have to stop taking alcohol or smoking to protect your growing baby from developing complications. The embryo now consists of three layers, the endoderm, the mesoderm and the ectoderm. The mesoderm (middle layer) will grow to become the heart, the bones, muscles and blood vessels. The ectoderm (outer layer) will grow into the nervous system, the brain, tooth enamel, nails, skin, and eye lenses. The endoderm (inner layer) will grow into digestive systems, breathing systems, gut, bladder, stomach and lungs. At this point, the amnion sac (this later develops to placenta) and yolk sac develop (this provides nourishment), with the amnion sac filling with amniotic fluid so as to protect your baby against shock. The yolk sac is vital in generating the blood and helps in proving nutrients to the embryo until the placenta is fully formed. The embryo develops a vascular network to transport oxygen, nutrients and blood though the umbilical cord. Your baby is now about the size of a poppy seed. At this time, you might experience bloating, mild bleeding and cramping, and mood swings.
Week 5: You may have confirmed your pregnancy though your abdomen does not increase up until you’re 14 weeks pregnant. Even if you haven’t gone for a pregnancy test, the fact that you have missed your period already is reason enough to know that you might be pregnant. You will experience the feeling of bloating as hormonal levels rise. Bloating is due to the effect of progesterone hormone. The vital organs of the baby are forming such as the central nervous system, the heart, the bones, and muscles, as the skeleton takes shape. As the baby’s heart grows, it should form the four chambers in order to pump blood. The ectoderm layer forms a groove, with the cells folding to form a neural tube, which develops into spinal cord and the brain. The placenta also develops to assist the umbilical cord in supplying nutrients. At this time, your baby has its blood vessels, a tube like heart and blood starts circulating. A string of blood vessels then connects you and the baby (this will grow to become the umbilical cord). Your baby looks like a tadpole at week 5. As for you, pregnancy symptoms will probably intensify at this period with the common ones including fatigue, sore breasts, and nausea just to mention a few.
Week 6: This should be the time to get your ultrasound to ensure the pregnancy is progressing well. Now, the embryo starts to develop the nose, the mouth and the ears, which may be picked by the ultrasound as black dots. Arms and legs start forming, together with the intestines, pancreases, lungs and the liver. The baby is about ¼ inch long, and may make some movements that are unnoticeable. The embryo is now covered with a thin layer of see-through skin. You will also experience different symptoms that are a characteristic of the first trimester (we will talk about these briefly later). Nonetheless, here are a few you should expect: morning sickness, tender breasts, vomiting, increased frequency in urination, moodiness, increased saliva, nausea, weird cravings etc.
Week 7: The developing baby is now about 10-13 mm in length, where facial features (mouth and tongue) are becoming pronounced. Formation of the eyes also starts with the retina and lens attaching. The baby develops a blood type as the appendix and the intestines are fully formed. The developing liver starts to synthesize red blood cells as the bones and muscles continue to grow. The embryo normally has a large forehead (this is because the brain develops much faster than other body parts). The nerve cells start to develop into the nervous system.
Week 8: At this point, you may develop varicose veins around your breasts with increased blood supply. The nipples start to discharge a yellowish substance known as colostrum’s as your body prepares for lactation. The baby is now preparing to move from embryonic to fetal stage, as the embryonic tail disappears. Measuring about 1 inch long, the baby weighs about 3 grams. The bones start to harden as the joints, wrists and elbows undergo ossification. The webbed hands and feet grows longer and start to separate into fingers; with the nose, mouth and jaw-line becoming pronounced. The placenta develops structures referred to as chorionic villi to attach to the uterus.
Week 9: As your uterus continues to grow, you experience severe mood swings as the level of hormone increases. Some physical features are in place such as the head, arms, and legs as the fetus begins to put on weight. The eyelids should now close to reopen at the 27th week of pregnancy. The gonads, mainly the ovaries or the testicles develop; though the gender may not be determinable from the appearance of organs. By now, the fetus should be about 22mm long measured from the head to bottom.
Week 10: The fetus continues to grow rapidly, and internal organs such as the brain, liver, kidneys and intestines start to work on their own. The jawbones also develop rapidly to contain the future milk teeth. The heartbeat of the fetus is now 2-3 times faster than yours, beating at 180 times a minute. You may notice the jerky movements the baby makes or see the effect on an ultrasound scan. The fetus continues to grow significantly larger over the course of the next three weeks.
Week 11: The changes in your physical appearance can now depict your pregnancy. Your abdomen distends due to slowing down of bowel movements in the small intestines. Your baby is now about 2 ½ inches long, weighing about 0.5 0unces, with the head making up half or third of the size. The fingers are countable by now, as the bones continue to harden. Still surrounded by the amniotic fluid, the fetus is learning to swallow parts of this fluid.
Week 12: This week signifies the end of your first semester. The baby’s brain can now make hormones on its own with body cells responding to the brain functions. The natural movements of your baby become more evident, such as twisting of the wrists and elbows, clenching and opening the fists as well as bending of the arms. The baby also develops the vocal cords, and the skeleton, which is formed from a soft tissue called cartilage, now starts to turn into a hard bone.