Pregnancy, while one of the most stressful and uncomfortable times of a woman’s life, is also one of the most exciting and remarkable times of a woman’s life with the heavy anticipation of delivering her baby. While it may be easy to get caught up in both the tiresome and exciting aspects of pregnancy, it is important to understand the different stages and things to look out for to ensure having a healthy baby. Pregnancy in most cases lasts roughly 40 weeks, starting from the first day of the last normal menstruation cycle. The stages are divided into three different trimesters. Below, each trimester is outlined with what happens and what to expect, the duration of each, what happens to the fetus and common complications that may arise to be on the lookout for.
The first trimester lasts from weeks 1 to 12 and during this time, the mother’s body experiences a few significant changes. Hormonal changes are significant and can cause symptoms very early, in addition to a ceased menstrual cycle. Changes a woman may experience include fatigue, tender and swollen breasts, an upset stomach that may or may not result in vomiting, cravings and/or distaste for specific foods, mood swings, constipation, the need to urinate often, headaches, and weight gain or loss.
For the baby, the first trimester is critical for development. During this period, the baby’s organs will become developed and in normal pregnancies, all organs will be developed at its completion.
During weeks 1 and 2, a woman is not actually pregnant because conception occurs about two weeks after the start of the last menstrual cycle. Physicians count forward 40 weeks from start of last menstrual cycle to establish the timeframe. One of the greatest risks to pregnancy at this stage is a blighted ovum which causes about half of the miscarriages between two and six weeks (often before the woman knows she is pregnant).
Fertilization, where the sperm and egg unite within the fallopian tubes, occurs at week 3 and the two forms a one-celled entity referred to as a zygote. It is possible for more than one egg to be released and fertilized or for the fertilized egg to split into two. Both scenarios can result in multiple zygotes. Shortly after fertilization, the zygote will divide into a cluster of cells, called a morula, while it travels down the fallopian tubes to the uterus where implantation occurs.
Implantation occurs at week 4 when the blastocyst, formally called the morula, burrows in the endometrium (uterine lining). The blastocyst contains an inner group of cells that become the embryo and an outer layer that becomes the placenta, which provides nourishment to the baby through the duration of the pregnancy.
Levels of HCG hormone will rapidly increase at week 5 and causes your ovaries to stop releasing eggs and increase production of estrogen and progesterone. This increase in hormones is what causes menstruation to stop as well as help the placenta grow. At this time, the embryo now has three distinct layers. The topmost layer, called the ectoderm, is where the baby’s outer layer of skin, central and peripheral nervous systems, eyes, and inner ears are derived from. The baby’s heart, circulatory system, and foundation for bones, ligaments, kidneys, and reproductive systems come from the middle layer of cells called the mesoderm. Finally, the baby’s lungs and intestines develop within the innermost layers of cells called the endoderm.
At week 6, growth starts to occur very quickly and the neural tube along the baby’s back will start to close where the brain and spinal cord will develop from. Additionally, at this time the heart and other organs will begin to form as well as structures that are needed for the development of the eyes and ears.
The baby’s brain and face begin to grow at week 7 and you can start to see what will be the nostrils and eyes as well as legs and arms.
Over the next five weeks, the baby’s nose, toes, arms, elbows, eyes and eyelids, genitals, and fingernails will form and start to become apparent. By week 11, the baby is officially called a fetus, the face is apparent, red blood cells begin to form in the liver, and genitalia begins developing. In week 12, the baby’s intestines will be in the abdomen. At this time, the fetus is still very small at around 2 and a half inches and will weigh around a half-ounce.
It is very important that during this time to prevent neural tube defects that the mother maintains a healthy diet with sufficient amounts of folic acid. The risk of having a miscarriage is highest during the first trimester, and those risks can be minimized by taking prenatal vitamins and avoiding smoking, alcohol, and drugs, including some prescription drugs. Physicians also recommend dietary changes including cutting caffeine, deli meats, and shellfish out of the diet to reduce the chances of a miscarriage. Additionally, smoking and the consumption of drugs and alcohol can cause serious pregnancy complications and birth defects and should be stopped during the pregnancy.
Other complications in the first trimester to be aware of include bleeding, hyperemesis gravidarum which is excessive vomiting, spontaneous abortions/miscarriages, ectopic pregnancies, and molar pregnancies. Each is briefly described below.
The second trimester occurs from week 13 through week 28. At the start, most mothers find that symptoms like nausea and fatigue have started to go away, but will start to experience their abdomen expanding more and more as the pregnancy goes on. During this time, the body must make changes to accommodate the growing baby, and a mother may experience symptoms including body aches, stretch marks, a line of their skin running from the belly button to pubic hairline, patches of dark skin matching on both sides of their face, carpal tunnel syndrome which causes numb or tingling sensations in the hands, itching, and swelling of the ankles, fingers, and face. Most women find this trimester easier than the first, and before it is over, the baby will noticeably begin to move inside the womb. Additionally, the baby will become able to hear and recognize the mother’s voice during this trimester.
By this time, all of the baby’s major organs will have been formed, but they are still not developed enough where a fetus could survive out of the womb.
At week 14, the gender can sometimes be seen but not always.
Some mothers will be able to feel fetal movement at this point, which is called quickening; however, not all mothers can as some will not be able to sense any movement until closer to 25 weeks.
During this time period, hearing starts to form and further lung development has started and will continue until week 25. By the end of week 17, although the lungs are readily developing, there are no alveoli developed yet, which are where the exchange of oxygen and carbon dioxide occurs, so respiration will still not be possible yet.
At this time, the ears will become clearly visible and the fetus may begin to start responding to sound.
At week 19, the ears, nose, and lips will become clearly apparent.
By week 20, the fetus will develop fine hair on its body; it will develop some scalp hair, and will become capable of producing two different types of antibodies, IgG and IgM.
At week 21, the fetus will on average be about 10.5 inches, able to suck and grasps, and may even have spells of hiccups.
At this point, a fetus has roughly a 33% chance of survival out of the womb, but survival without major disease is 2%. Additionally, the fetus will begin to have rapid eye movements during sleep.
At week 24, the lungs are becoming more and more developed and now, a fetus has roughly a 65% chance of survival out of the womb and survival without major disease around 9%.
At this end of this week, lung development is coming to an end and respiration becomes possible. A fetus now will have roughly an 81% chance of survival out of the womb and survival without major disease around 25%.
At week 26, the fetus will be able to open and close its eyelids as well as respond to surrounding sounds.
Finally, at the completion of the second trimester, the fetus will on average weigh 2.3 pounds and is roughly 14.2 inches long. At this point, the chance of survival outside of the womb jumps to 94% with a chance of survival without major disease at 50%.
During this time period, a mother should consider having screening test performed based on medical history, family history, or genetic issues that could cause complications and the baby at risk. It is also important to make sure that the baby’s heart, lungs, kidneys, and brain are functioning properly, which can be determined by an anatomy ultrasound. Gestational diabetes can also arise during the second trimester from weeks 26-28. A mother should be tested to ensure that her body is reacting correctly to sugar during the pregnancy.
While the risks of a miscarriage are reduced once you reach the second trimester, infections or abnormalities of the uterus or placenta can cause a miscarriage. One of the most common complications seen in the second trimester is an incompetent cervix, where the cervix is both weaker and softer than it needs to be and may open too early. The cervix can become dilated and shorten as the baby becomes larger and pressure is increased, which can ultimately result in miscarriage, early delivery, or early rupture of the membranes. If caught early, there are treatments available that can significantly reduce the risks of a miscarriage or early delivery.
Additionally, placental abruptions are also a common complication seen during the second trimester. A placental abruption occurs when the placenta separates from the uterus too early and when half or more separates, a miscarriage becomes possible. Trauma to the abdomen and consumption of drugs, alcohol, and smoking significantly increase the risks of having a placental abruption. Symptoms to be aware of include bleeding and both cramping and tenderness of the uterus.
During the final stage of pregnancy, a mother will likely experience many of the same discomforts as in the previous two trimesters, and additionally, they may experience some difficulty breathing and more frequent urination. There is no need for concern, however, as these symptoms are just results of the baby growing and putting more pressure on the surrounding organs. Mothers may also experience heartburn, increased swelling of the ankles, fingers, and face, hemorrhoids, difficulty sleeping, contractions, tender breast, leaking of colostrum which is watery premature milk, and their belly button may stick out.
At this point, the fetus will have eyelashes and be covered with caseosa, a substance that provides a protective film with anti-infective properties.
By the end of the 31 week, the fetus will be on average 16.4 inches in length and roughly 4 pounds.
The fetus will now be in the process of forming muscle and storing body fat. Additionally, in males the testicles will have begun to descend.
At this point, the fetus is now a preterm.
The fetus now is considered an early term and on average roughly 20 inches long 7 pounds.
The fetus is now finally full term.
Gestational diabetes can arise during the third trimester and causes high blood sugar that could affect both your baby’s health and your pregnancy. This can be controlled by diet, exercise, and medication. If your blood sugar is not under control, complications during birth are more likely to occur. Usually, in the case of gestational diabetes, blood sugar will return to normal levels after delivery. It is important to note, however, that if you have a history of gestational diabetes; it can put you at higher risks of type 2 diabetes.
Preeclampsia is another third trimester complication to be aware of. Preeclampsia results in high blood pressure and damage to other organs, usually, the liver and kidneys. The only cure for preeclampsia is an early delivery and if left untreated, can lead to serious and sometimes fatal complications for you and the baby.
Preterm labor may also arise in the third trimester, and occurs when your body prepares to give birth too early, characterized as earlier than three weeks prior to your due date. In some cases premature labor will lead to premature delivery, however, there are many treatments a physician can provide to delay or prevent a premature delivery.
Preterm rupture of the membranes, where the amniotic membrane that surrounds the baby ruptures before the week 37, may also occur. If it does, there is an increased risk of infection as well as a premature delivery.
It is also important to be aware of placenta previa, which is a condition where the placenta comes out first and blocks the opening of the cervix. If you have previously had a cesarean section or uterine surgery you are at greater risks for this complication. Additionally, smoking significantly enhances the risks of developing this condition.
Intrauterine growth restriction is a condition where the fetus is not growing at the normal rate and as a result, the unborn baby is smaller than it should be. This puts the baby at risks for certain problems including low birth weight, difficulty undergoing the stress of delivery, reduced oxygen levels, hypoglycemia, an insufficient immune system, body temperature abnormalities, and very high counts of red blood cells. This complication is often able to be managed, but in the most serious cases it can lead to long-term growth problems in the child as well as stillbirth.
Post-term pregnancy is a complication where they baby, after 42 weeks, has still not been born. This can result in risks for both the mother and infant, but is often treated by inducing labor.
Lastly, malpresentation is a complication that sometimes arises where the infants head is in abnormal positions relative to where it should be. This can result in both prolonged and sometimes obstructed labor where a caesarean section may be necessary.