Pregnancy is the carrying of one or more offspring in an embryonic or fetal stage of development by females, between the stages of conception and birth.
Childbirth usually occurs about 38 weeks from fertilization, approximately 40 weeks from the start of the last menstruation. Thus, pregnancy lasts about nine months. Though this time length is an average, the actual length of pregnancy depends on various factors, such as fetal development and health and the mother's health. In general, the first pregnancy tends to last longer than subsequent pregnancies. Fewer than 10% of births occur on the due date; 50% of births are within a week of the due date, and almost 90% are within two weeks.
The due date is typically calculated as 40 weeks from the last menstrual period.
Before pregnancy begins, a female oocyte (egg) must join with a sperm in a process referred to in medicine as "fertilization" or commonly known as "conception." Fertilization usually occurs through the act of sexual intercourse, in which a man ejaculates inside a woman's vagina, thus releasing his sperm. However, artificial insemination has made it possible for women to become pregnant when pre-existing medical conditions from either the woman or the man make fertilization through sexual intercourse difficult, or if a woman chooses to become pregnant without a male partner.
After fertilization, the combination of the egg and sperm is called a zygote. The zygote becomes embedded in the uterus wall where it can begin growth. The human zygote undergoes cellular division to become an embryo. The term embryo is used until the end of the eighth week of gestational age, when it is then called a fetus or unborn baby until birth.
Human pregnancy is divided into three trimester periods. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester, the development of the fetus can be monitored and diagnosed more easily. The third trimester often marks the beginning of viability, or the ability of the fetus to survive, with or without medical help, outside of the mother's womb.
According to the Centers for Disease Control and Prevention (CDC), nearly four million American women give birth every year in the United States.
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Once pregnancy occurs, hormonal changes take place in the body of the woman. Also, development of the fetus in the womb produces many biochemical changes in the mother.
There are signs associated with pregnancy. The most common is a missed menstrual period. However, since all women do not have regular menstrual cycles, it is important to watch for other pregnancy signs such as: breast tenderness, nausea, heartburn, extreme tiredness, and frequent urination. (see Heading:Diagnosis)
Even if a woman has some or all symptoms it is important to reconfirm the diagnosis with a pregnancy test. This test will detect the presence of a hormone called chorionic gonadotropin, which is produced by the placenta and it is present in the blood and urine of the expecting woman.
Pregnancy is typically broken into three periods, or trimesters, each of about three months. While there are no hard and fast rules, these distinctions are useful in describing the changes that take place over time.
First trimester: Traditionally, doctors have measured pregnancy from a number of convenient points, including the day of last menstruation, ovulation, fertilization, implantation, and chemical detection. In medicine, pregnancy is often defined as beginning when the developing zygote becomes implanted into the endometrial lining of a woman's uterus to begin growth.
Most pregnant women do not have any specific signs or symptoms of implantation, although it is not uncommon to experience light bleeding at implantation. In some cases where complications may have arisen, the fertilized egg might implant itself in the fallopian tubes or the cervix, causing an ectopic pregnancy. Some women will also experience cramping during their first trimester. This cramping is usually of no concern unless there is spotting or bleeding as well. The outer layers of the embryo grow and form a placenta, for the purpose of receiving essential nutrients through the uterine wall. The umbilical cord connects the unborn baby to the placenta. The developing embryo undergoes tremendous growth and changes during the process of embryonic and fetal development.
Morning sickness afflicts about 70% of all pregnant women, typically only in the first trimester. Most miscarriages occur during this period.
Second trimester: Months four through six of the pregnancy are called the second trimester. Most women feel more energized in this period than the first or third trimester and begin to put on weight as the symptoms of morning sickness subside and eventually fade away. Although the fetus begins moving and takes a recognizable human shape during the first trimester, it is not until the second trimester that movement of the fetus, often referred to as "quickening," can be felt. This typically happens by the fourth month. The teeth are now formed inside the unborn baby's gums and the reproductive organs can be recognized allowing a doctor to know the sex of the child.
Third trimester: In the last or third trimester, final weight gain takes place and the fetus begins to move regularly. The mother's belly button will sometimes protrude due to her growing belly. This period of her pregnancy can be uncomfortable, causing symptoms such as weak bladder control and back-ache. Movement of the fetus becomes stronger and more frequent and the fetus prepares for viability outside the womb through improved brain, eye, and muscle function. The mother can feel the unborn baby moving and rolling, which may cause pain or discomfort around the mother's ribs.
If a fetus is born early or prematurely in the third trimester, advanced medical technology can help the baby survive. In most systems of human pregnancy, prematurity is considered to occur when the baby is born sooner than 37 weeks after the beginning of the last menstrual period (LMP). The opposite condition, postmature birth, is defined as birth more than 42 weeks after the LMP.
Getting early and regular prenatal care is one of the best ways to promote a healthy pregnancy. Prenatal care is more than just healthcare. Prenatal care includes education and counseling about how to handle different aspects of pregnancy, such as nutrition and physical activity, what to expect from the birth itself, and basic skills for caring for the infant.
Prenatal visits also give the woman and her family a chance to talk to a healthcare provider about any questions or concerns related to pregnancy, birth, or parenthood.
Many healthcare providers recommend that a woman who is only thinking about getting pregnant see a healthcare provider about preconception health. Also, if the individual thinks they are pregnant she should also see a healthcare provider. There are steps she can take to reduce the risk of certain problems. The objective of prenatal care is to monitor the health of the pregnant mother and her unborn baby. It is important to visit the doctor as soon as an individual suspects they are pregnant. At each visit, a doctor will examine the individual and make sure that the baby and the mother are healthy. This examination includes: monitoring weight gain or loss, blood pressure, circumference of the abdomen, position of the fetus, and fetal heartbeat. Such variables are closely followed during the course of the pregnancy.
A doctor may schedule monthly visits during the first two trimesters (from week one to week 28 of pregnancy), every two weeks from 28-36 of pregnancy, and weekly after week 36 (until the day of delivery that could be between week 38-40 weeks).
Food and nutrition during pregnancy: It is important for an expectant mother to eat a healthy diet. Unless she has a specific health problem (such as diabetes mellitus or heart disease) common sense nutritional advice should be followed: balancing carbohydrates, fat, and proteins and eating a variety of foods, including dairy products and several fruits and vegetables, daily. A pregnant woman should consult her obstetrician for specific advice. Some specific nutritional needs for pregnancy include:
Folic acid, also called folate or vitamin B9, is strongly recommended by healthcare professionals at the start of pregnancy and even before conception. Folic acid is needed for the closing of fetus' neural tube. The neural tube is the fetus's precursor to the brain and spinal cord. Folic acid thus helps prevent spina bifida, a very serious birth defect. Folates are abundant in spinach (fresh, frozen or canned) and are also found in green vegetables, salads, melon, and eggs. In the United States and Canada, most wheat products, such as flour or noodles, are supplemented with folic acid.
Minerals, such as calcium and iron, are particularly needed by the rapidly growing fetus. Pregnant women should eat enough dairy products (for calcium) and red meat (for iron) if they are not lactose intolerant or vegetarian. Women who do not eat dairy or meat can obtain calcium and iron from fortified soy milk and juice, soybeans, and certain leafy greens. Calcium is effective only if women also obtain enough vitamin D. Vitamin D can be made in the body after exposure to ultraviolet rays from the sun or from food sources. Although milk is fortified with vitamin D, dairy products made from milk, such as cheese and ice creams, are generally not fortified with vitamin D. Cold water fish such as salmon, mackerel, tuna, and sardines also good sources of vitamin D.
Healthcare providers may prescribe iron supplements if pregnant women develop anemia. Anemia, one of the more common blood disorders, occurs when the level of healthy red blood cells (RBCs) in the body becomes too low. RBCs contain hemoglobin, which carries oxygen to the body's tissues.
Fluoride helps to build strong teeth by changing the nature of calcium crystals. If drinking water or table salt does not contain fluoride, it is recommended by healthcare professionals to take fluoride supplements at the end of pregnancy and during breastfeeding. However, high doses of fluoride are toxic. In many American cities, drinking water is supplemented with fluoride.
Oils from salmon, trout, tuna, herring, sardine, mackerel, eggs, and some chicken contain omega-3 fatty acids that are needed to build brain tissue. Intake of omega-3 fatty acids during pregnancy may provide nutrition for proper brain and retina development of the fetus. However, large fish such as tuna and swordfish may contain high levels of mercury. Mercury can be toxic to the fetus and the mother. Eating omega-3 rich fish two or three times a week is recommended (no more than 12 ounces/week of low mercury fish should be consumed). Omega-3 fatty acids are also present in walnuts, flaxseed, and seaweed.
Dangerous bacteria or parasites, particularly Listeria and Toxoplasma, may contaminate foods. To avoid those two hazards, hygiene rules should be strictly adhered to, including carefully washing of fruits and raw vegetables, cooking leftovers and meats appropriately, and avoiding raw-milk cheeses (due to Listeria). The label will state if the cheese is from raw milk. It is best to try to avoid contact with cat feces (due to Toxoplasma).
It is best to maintain a healthy weight and diet and get regular physical activity before, during, and after pregnancy. It is recommended by healthcare professionals to avoid smoking, alcohol, or drug use before, during, and after pregnancy. These factors increase the chances of damage to the growing fetus.
Labor and delivery
Labor and delivery, or childbirth, is the process by which an infant is born. When a baby is ready to be born, the mother will go through labor.
Common signs of labor: A common sign that labor is near is lightening or when the baby "drops" or moves into position within the pelvis. Lightening may occur two to four weeks prior to labor in first-time mothers and often not until labor begins in mothers who have previously had children.
The mother's abdomen usually appears lower and more protruding.
The mother may experience a greater ease in breathing, relief from heartburn, and an ability to eat larger portions. However, the lower position of the baby together with its greater size can lead to: increased backache and sacroiliac (the two joints where the hip bones connect to the sacrum) discomfort; increased awkwardness in walking; and increased frequency of urination.
Frequent bowel movements may be experienced within 48 hours of labor, cleansing the lower bowel in preparation for birth.
Diarrhea or flu-like symptoms without fever may be felt before labor. Indigestion, nausea, or vomiting are common a day or so before labor begins.
Increased vaginal discharge during the last few weeks of pregnancy as the body prepares for the passage of the baby through the birth canal may occur.
Increased Braxton-Hicks contractions during the last weeks of pregnancy, which are "practice" contractions that prepare the uterus for labor and may cause some effacement and dilation (thinning and opening) of the cervix, may occur. These contractions do not ordinarily cause pain but may be sufficiently strong and regular to be confused with true labor. This is referred to as false labor.
Possible "bloody show" or the release of slightly brown, pink, or blood-tinged mucus from effacement and dilation (the thinning and opening) of the cervix, causing the mucus plug to be released from the cervix, may occur.
An initial sign of labor is when the "water breaks." The amniotic sac is a fluid-filled membrane that cushions the fetus in the uterus. The sac leaks or breaks releasing amniotic fluid before labor begins. If this happens, the individual may notice a trickle of fluid or a more obvious gush.
Labor contractions are the periodic tightening and relaxing of the uterine muscle, the largest muscle in a woman's body. Contractions let the woman know labor is starting. Most doctors suggest going to a hospital when the contractions are five minutes apart and lasting 60 seconds and the individual has had this activity for about an hour. Contractions range from mild tightening to constant muscle spasms in the abdominal area. Contractions may be irregular at first but usually become regular. They get longer, stronger, and closer together as time progresses. Many mothers describe contractions that occur in early labor as similar to menstrual cramps, or as severe gas pains, which may be confused with flu symptoms or intestinal disorders. Walking usually makes the contractions stronger. Lying down does not make them go away. Often, the contractions begin in the back and move to the front.
During the first stage of labor, the cervix slowly opens, or dilates, to about four inches wide. At the same time, the cervix becomes thinner. This is called effacement. The individual should not push until the uterus is fully effaced and dilated. As the cervix dilates, some individuals describe cramping and pressure, similar to what would be felt during menstruation. When is the cervix is completely dilated, the baby delivery stage starts. Crowning is when the baby's scalp comes into view. Shortly afterward, the baby is born. The placenta that nourished the baby follows. Mothers and babies are monitored closely during labor. Most women are healthy enough to have a baby through normal vaginal delivery, meaning that the baby comes down the birth canal without surgery.
Pain in labor is a nearly universal experience for childbearing women giving birth naturally. Tears (rips) in the vagina during delivery will occur. In order to prevent these vaginal tears from occurring, doctors will often perform an episiotomy. In this procedure, an incision is made in the perineum, which is the area between the vagina and the anus. This incision allows the vaginal opening to enlarge, thereby giving the baby more space to emerge from.
A typical labor for a first time mother is eight to 14 hours, and is usually shorter for a second or subsequent birth.
Labor induction: Sometimes, if labor has not started on its own, doctors use medicines to make a woman's labor begin so that she can deliver the baby vaginally. This is called "labor induction" or induced labor. The most common reason for labor induction is that the pregnancy has gone two weeks or more past the due date. The baby may get too big if the mother carries it this far past the due date. The fetus may not be able to get enough food from inside the body. A doctor might also recommend labor induction if: the woman's water breaks before she goes into labor; she has high blood pressure; she has a serious infection; or if she has diabetes.
There are several ways to induce labor. Toward the end of pregnancy, the cervix (the opening to the uterus, or womb) gets soft. It may even open up a little. A doctor will check to see if the cervix is getting soft and opening up. If it is not, a doctor may put a medicine, called oxytocin (Pitocin®), into the woman's vagina near the cervix. Oxytocin will soften and open the cervix up, helping to start the contractions and get them strong and regular. A doctor may also "break the water" or use a finger to separate the cervix from the membranes (tissues) around the baby's head. This often makes labor start. Sometimes it may take two to three days to induce labor, but this is rare.
C-section: If labor will not start with medicine, a cesarean section (also called a "C" section) may be necessary.. A Cesarean section (C-section) is surgery to deliver a baby. The baby is taken out through the mother's abdomen. In the United States, about one in four women have their babies this way. Most C-sections are done when unexpected problems happen during delivery. These include: carrying more than one baby; health problems in the mother, such as diabetes or high blood pressure; the position of the baby; not enough room for the baby to go through the vagina; or signs of distress in the baby. The surgery is relatively safe for mother and baby. Still, it is major surgery and carries risks. It also takes longer to recover from a C-section than from vaginal birth. After healing, the incision may leave a weak spot in the wall of the uterus. This could cause problems with an attempted vaginal birth later. However, more than half of women who have a C-section can give vaginal birth later. Individuals can discuss options during childbirth before the due date in order to alleviate any added stress during labor and delivery.
causes of pregnancy
Pregnancy occurs with the fertilization of a woman's egg by a man's sperm, called conception. Fertility drugs, such as clomiphene (Clomid®), may improve a woman's odds of achieving pregnancy. Some of the most common causes of female infertility include polycystic ovarian syndrome, fibroids, and endometriosis. However, there are several other reasons why a woman may experience fertility problems, such as ovulatory disorders (like anovulation or the inability to ovulate), premature ovarian failure, and uterine factors. Egg quality also plays a role in infertility in many women. There are good and bad eggs from the very start in any female's body, but usually the number of eggs of superior quality are present at a higher volume at a younger age than after 30. Egg quality is also affected by external sources like radiation therapy, smoking, chemotherapy, and health conditions like endometriosis. Endometriosis is a condition in which the tissue that normally lines the uterus (endometrium) grows in other areas of the body, causing pain, irregular bleeding, and possible infertility. In men, hormone disorders, illness, reproductive anatomy trauma and obstruction, and sexual dysfunction can temporarily or permanently affect sperm and prevent conception. Some disorders become more difficult to treat the longer they persist without treatment. According to the National Institutes of Health (NIH), male infertility is involved in approximately 40% of the 2.6 million infertile married couples in the United States. One-half of these men experience irreversible infertility and cannot father children, and a small number of these cases are caused by a treatable medical condition.