FACTS ON PREGNANCY
Pregnant woman at 26 weeks
A woman eight months pregnant
Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the womb of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Human pregnancy is the most studied of all mammalian pregnancies. Childbirth usually occurs about 38 weeks after conception; i.e., approximately 40 weeks from the last normal menstrual period (LNMP) in humans. The World Health Organization defines normal term for delivery as between 37 weeks and 42 weeks.
Terminology
One scientific term for the state of pregnancy is gravid, and a pregnant female is sometimes referred to as a gravida.[1] Neither word is used in common speech. Similarly, the term “parity” (abbreviated as “para”) is used for the number of previous successful live births. Medically, a woman who has never been pregnant is referred to as a “nulligravida”, a woman who is (or has been only) pregnant for the first time as a “primigravida”[2], and a woman in subsequent pregnancies as a multigravida or “multiparous”.[1][3][4] Hence, during a second pregnancy a woman would be described as “gravida 2, para 1” and upon live delivery as “gravida 2, para 2”. An in-progress pregnancy, as well as abortions, miscarriages, or stillbirths account for parity values being less than the gravida number, whereas a multiple birth will increase the parity value. Women who have never carried a pregnancy achieving more than 20 weeks of gestation age are referred to as “nulliparous”.[5]
The term embryo is used to describe the developing offspring during the first 8 weeks following conception, and the term fetus is used from about 2 months of development until birth.[6][7]
In many societies’ medical or legal definitions, human pregnancy is somewhat arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of prenatal development. The first trimester carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester, the development of the fetus can be more easily monitored and diagnosed. The beginning of the third trimester often approximates the point of viability, or the ability of the fetus to survive, with or without medical help, outside of the uterus.[8]
Progression
Stages in prenatal development, with weeks and months numbered from last menstrual period.
Initiation
The initial stages of human embryogenesis.
Pregnancy occurs as the result of the female gamete or oocyte merging with the male gamete, spermatozoon, in a process referred to, in medicine, as “fertilization”, or more commonly known as “conception”. After the point of “fertilization”, it is referred to as a zygote or fertilized egg. The fusion of male and female gametes usually occurs through the act of sexual intercourse, resulting in spontaneous pregnancy. However, the advent of artificial insemination and in vitro fertilisation have also made achieving pregnancy possible in cases where sexual intercourse does not result in fertilization (e.g., through choice or male/female infertility).
Perinatal period
Perinatal defines the period occurring “around the time of birth”, specifically from 22 completed weeks (154 days) of gestation (the time when birth weight is normally 500 g) to 7 completed days after birth.[9]
Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.
Postnatal period
The postnatal period begins immediately after the birth of a child and then extends for about six weeks. During this period the mother’s body returns to prepregnancy conditions as far as uterus size and hormone levels are concerned.
Duration
The expected date of delivery (EDD) is 40 weeks counting from the first day of the last menstrual period (LMP), and birth usually occurs between 37 and 42 weeks.[10] The actual pregnancy duration is typically 38 weeks after conception. Though pregnancy begins at conception, it is more convenient to date from the first day of a woman’s last menstrual period, or from the date of conception if known. Starting from one of these dates, the expected date of delivery can be calculated. Forty weeks is 9 months and 6 days, which forms the basis of Naegele’s rule for estimating date of delivery. More accurate and sophisticated algorithms take into account other variables, such as whether this is the first or subsequent child (i.e., pregnant woman is a primip or a multip, respectively), ethnicity, parental age, length of menstrual cycle, and menstrual regularity.
Pregnancy is considered “at term” when gestation attains 37 complete weeks but is less than 42 (between 259 and 294 days since LMP). Events before completion of 37 weeks (259 days) are considered preterm; from week 42 (294 days) events are considered postterm.[11] When a pregnancy exceeds 42 weeks (294 days), the risk of complications for woman and fetus increases significantly.[10][12] As such, obstetricians usually prefer to induce labour, in an uncomplicated pregnancy, at some stage between 41 and 42 weeks.[13][dead link][14]
Recent medical literature prefers the terminology preterm and postterm to premature and postmature. Preterm and postterm are unambiguously defined as above, whereas premature and postmature have historical meaning and relate more to the infant’s size and state of development rather than to the stage of pregnancy.[15][16]
Fewer than 5% of births occur on the due date; 50% of births are within a week of the due date, and almost 90% within 2 weeks.[17] It is much more useful, therefore, to consider a range of due dates, rather than one specific day, with some online due date calculators providing this information.
Accurate dating of pregnancy is important, because it is used in calculating the results of various prenatal tests (for example, in the triple test). A decision may be made to induce labour if a fetus is perceived to be overdue. Furthermore, if LMP and ultrasound dating predict different respective due dates, with the latter being later, this might signify slowed fetal growth and therefore require closer review.
The age of viability has been receding because of continued medical progress. Whereas it used to be 28 weeks, it has been brought back to as early as 23, or even 22 weeks in some countries. Unfortunately, there has been a profound increase in morbidity and mortality associated with the increased survival to the extent it has led some to question the ethics and morality of resuscitating at the edge of viability.[citation needed]
Childbirth
Childbirth is the process whereby an infant is born. It is considered by many to be the beginning of the infant’s life, and age is defined relative to this event in most cultures.
A woman is considered to be in labour when she begins experiencing regular uterine contractions, accompanied by changes of her cervix — primarily effacement and dilation. While childbirth is widely experienced as painful, some women do report painless labours, while others find that concentrating on the birth helps to quicken labour and lessen the sensations. Most births are successful vaginal births, but sometimes complications arise and a woman may undergo a cesarean section.
During the time immediately after birth, both the mother and the baby are hormonally cued to bond, the mother through the release of oxytocin, a hormone also released during breastfeeding.
Diagnosis
The beginning of pregnancy[18] may be detected in a number of different ways, either by a pregnant woman without medical testing, or by using medical tests with or without the assistance of a medical professional.
Most pregnant women experience a number of symptoms[19] , which can signify pregnancy. The symptoms can include nausea and vomiting, excessive tiredness and fatigue, craving for certain foods not normally considered a favorite, and frequent urination particularly during the night.
A number of early medical signs are associated with pregnancy.[20][21] These signs typically appear, if at all, within the first few weeks after conception. Although not all of these signs are universally present, nor are all of them diagnostic by themselves, taken together they make a presumptive diagnosis of pregnancy. These signs include the presence of human chorionic gonadotropin (hCG) in the blood and urine, missed menstrual period, implantation bleeding that occurs at implantation of the embryo in the uterus during the third or fourth week after last menstrual period, increased basal body temperature sustained for over 2 weeks after ovulation, Chadwick’s sign (darkening of the cervix, vagina, and vulva), Goodell’s sign (softening of the vaginal portion of the cervix), Hegar’s sign (softening of the uterus isthmus), and pigmentation of linea alba – Linea nigra, (darkening of the skin in a midline of the abdomen, caused by hyperpigmentation resulting from hormonal changes, usually appearing around the middle of pregnancy).[20][21]
Pregnancy detection can be accomplished using one or more various pregnancy[18] tests, which detect hormones generated by the newly formed placenta. Clinical blood and urine tests can detect pregnancy 12 days after implantation [22], which is as early as 6 to 8 days after fertilization. Blood pregnancy tests are more accurate than urine tests.[23] Home pregnancy tests are personal urine tests, which normally cannot detect a pregnancy until at least 12 to 15 days after fertilization. Both clinical and home tests can only detect the state of pregnancy, and cannot detect the age of the embryo.
In the post-implantation phase, the blastocyst secretes a hormone named human chorionic gonadotropin, which in turn stimulates the corpus luteum in the woman’s ovary to continue producing progesterone. This acts to maintain the lining of the uterus so that the embryo will continue to be nourished. The glands in the lining of the uterus will swell in response to the blastocyst, and capillaries will be stimulated to grow in that region. This allows the blastocyst to receive vital nutrients from the woman.
Despite all the signs, some women may not realize they are pregnant until they are quite far along in their pregnancy, in some cases not even until they begin labour. This can be caused by many factors, including irregular periods (quite common in teenagers), certain medications (not related to conceiving children), and obese women who disregard their weight gain. Others may be in denial of their situation.
An early sonograph can determine the age of the pregnancy fairly accurately. In practice, doctors typically express the age of a pregnancy (i.e., an “age” for an embryo) in terms of “menstrual date” based on the first day of a woman’s last menstrual period, as the woman reports it. Unless a woman’s recent sexual activity has been limited, she has been charting her cycles, or the conception is the result of some types of fertility treatment (such as IUI or IVF), the exact date of fertilization is unknown. Without symptoms such as morning sickness, often the only visible sign of a pregnancy is an interruption of the woman’s normal monthly menstruation cycle, (i.e., a “late period”). Hence, the “menstrual date” is simply a common educated estimate for the age of a fetus, which is an average of 2 weeks later than the first day of the woman’s last menstrual period. The term “conception date” may sometimes be used when that date is more certain, though even medical professionals can be imprecise with their use of the two distinct terms. The due date can be calculated by using Naegele’s rule. The expected date of delivery may also be calculated from sonogram measurement of the fetus. This method is slightly more accurate than methods based on LMP.[24] The beginning of labour, which is variously called confinement or childbed, begins on the day predicted by LMP 3.6% of the time and on the day predicted by sonography 4.3% of the time.[citation needed]
Diagnostic criteria are: Women who have menstrual cycles and are sexually active, a period delayed by a few days or weeks is suggestive of pregnancy; elevated B-hcG to around 100,000 mIU/mL by 10 weeks of gestation.[2]
Physiology
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 embryo becomes implanted into the endometrial lining of a woman’s uterus. 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. Most pregnant women do not have any specific signs or symptoms of implantation, although it is not uncommon to experience minimal bleeding at implantation. Some women will also experience cramping during their first trimester. This is usually of no concern unless there is spotting or bleeding as well. After implantation the uterine endometrium is called the decidua. The placenta, which is formed partly from the decidua and partly from outer layers of the embryo, is responsible for transport of nutrients and oxygen to, and removal of waste products from the fetus. The umbilical cord is the connecting cord from the embryo or fetus to the placenta. The developing embryo undergoes tremendous growth and changes during the process of fetal development.
Morning sickness occurs in about seventy percent of all pregnant women and typically improves after the first trimester.[25][dead link] Although it is described as “morning sickness” many woman experience this sickness during afternoon, evening, and even throughout the entire day.
In the first 12 weeks of pregnancy, the nipples and areolas darken due to a temporary increase in hormones.[26]
Most miscarriages occur during this period.[citation needed]
Second trimester
Weeks 12 to 24 of the pregnancy are called the second trimester. Most women feel more energized in this period, and begin to put on weight as the symptoms of morning sickness subside and eventually fade away.
In the 20th week the uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy. Although the fetus begins to move 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 in the fourth month, more specifically in the 20th to 21st week, or by the 19th week if the woman has been pregnant before. However, it is not uncommon for some women not to feel the fetus move until much later. The placenta fully functions at this time and the fetus makes insulin and urinates. The reproductive organs distinguish the fetus as male or female.
Third trimester
Comparison of growth of the abdomen between 26 weeks and 40 weeks gestation.
Final weight gain takes place, which is the most weight gain throughout the pregnancy. The fetus will be growing the most rapidly during this stage, gaining up to 28g per day. The woman’s belly will transform in shape as the belly drops due to the fetus turning in a downward position ready for birth. During the second trimester, the woman’s belly would have been very upright, whereas in the third trimester it will drop down quite low, and the woman will be able to lift her belly up and down. The fetus begins to move regularly, and is felt by the woman. Fetal movement can become quite strong and be disruptive to the woman. The woman’s navel will sometimes become convex, “popping” out, due to her expanding abdomen. This period of her pregnancy can be uncomfortable, causing symptoms like weak bladder control and backache. Movement of the fetus becomes stronger and more frequent and via improved brain, eye, and muscle function the fetus is prepared for ex utero viability. The woman can feel the fetus “rolling” and it may cause pain or discomfort when it is near the woman’s ribs and spine.
There is head engagement in the third trimester, that is, the fetal head descends into the pelvic cavity so that only a small part (or nothing) of it can be felt abdominally.[27]
It is during this time that a baby born prematurely may survive. The use of modern medical intensive care technology has greatly increased the probability of premature babies surviving, and has pushed back the boundary of viability to much earlier dates than would be possible without assistance.[28] In spite of these developments, premature birth remains a major threat to the fetus, and may result in ill-health in later life, even if the baby survives.
Embryonic and fetal development
Prenatal development is divided into two primary biological stages. The first is the embryonic stage, which lasts for about two months. At this point, the fetal stage begins. At the beginning of the fetal stage, the risk of miscarriage decreases sharply,[29] all major structures including hands, feet, head, brain, and other organs are present, and they continue to grow and develop. When the fetal stage commences, a fetus is typically about 30 mm (1.2 inches) in length, and the heart can be seen beating via sonograph; the fetus bends the head, and also makes general movements and startles that involve the whole body.[30] Some fingerprint formation occurs from the beginning of the fetal stage.[31]
Electrical brain activity is first detected between the 5th and 6th week of gestation, though this is still considered primitive neural activity rather than the beginning of conscious thought, something that develops much later in fetation. Synapses begin forming at 17 weeks, and at about week 28 begin multiply at a rapid pace which continues until 3–4 months after birth. It isn’t until week 23 that the fetus can survive, albeit with major medical support, outside of the womb. It is not until then that the fetus possesses a sustainable human brain.[32]
 Embryo at 4 weeks after fertilization[33] |
 Fetus at 8 weeks after fertilization[34] |
 Fetus at 18 weeks after fertilization[35] |
 Fetus at 38 weeks after fertilization[36] |
 Relative size in 1st month (simplified illustration) |
 Relative size in 3rd month (simplified illustration) |
 Relative size in 5th month (simplified illustration) |
 Relative size in 9th month (simplified illustration) |
One way to observe prenatal development is via ultrasound images. Modern 3D ultrasound images provide greater detail for prenatal diagnosis than the older 2D ultrasound technology.[37] While 3D is popular with parents desiring a prenatal photograph as a keepsake,[38] both 2D and 3D are discouraged by the FDA for non-medical use,[39][dead link] but there are no definitive studies linking ultrasound to any adverse medical effects.[40] The following 3D ultrasound images were taken at different stages of pregnancy:
 75-mm fetus (about 14 weeks gestational age) |
 Fetus at 17 weeks |
 Fetus at 20 weeks |
Some people are confused about the differences between an ultrasound and a sonogram. An ultrasound is the actual machine that lets you observe pregnancy. A sonogram is the image of the baby that the ultrasound produces. 4D Ultrasounds take 3D sonograms. Some people refer to the procedure as prenatal imaging, 3D imaging, a 3D scan, or 4D scan.
Maternal physiological changes
During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications. The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required. Levels of progesterone and oestrogens rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle. The woman and the placenta also produce many hormones.
Management
Prenatal medical care is the medical and nursing care recommended for women before and during pregnancy. The aim of good prenatal care is to detect any potential problems early, to prevent them if possible (through recommendations on adequate nutrition, exercise, vitamin intake etc), and to direct the woman to appropriate specialists, hospitals, etc. if necessary.
Nutrition
A balanced, nutritious diet is an important aspect of a healthy pregnancy. Eating a healthy diet, balancing carbohydrates, fat, and proteins, and eating a variety of fruits and vegetables, usually ensures good nutrition. Those whose diets are affected by health issues, religious requirements, or ethical beliefs may choose to consult a health professional for specific advice.
Adequate periconceptional folic acid (also called folate or Vitamin B9) intake has been proven to limit fetal neural tube defects, preventing spina bifida, a very serious birth defect. The neural tube develops during the first 28 days of pregnancy, explaining the necessity to guarantee adequate periconceptional folate intake.[41][42] Folates (from folia, leaf) are abundant in spinach (fresh, frozen, or canned), and are found in green leafy vegetables e.g. salads, beets, broccoli, asparagus, citrus fruits and melons, chickpeas (i.e. in the form of hummus or falafel), and eggs. In the United States and Canada, most wheat products (flour, noodles) are fortified with folic acid.[43] Cosmetically, a deficiency in B vitamins can become apparent through increased pigmentation over areas of the body such as the forehead and cheeks (a condition known as ‘pregnancy mask’ or melasma).[44]
DHA omega-3 is a major structural fatty acid in the brain and retina, and is naturally found in breast milk. It is important for the woman to consume adequate amounts of DHA during pregnancy and while nursing to support her well-being and the health of her infant. Developing infants cannot produce DHA efficiently, and must receive this vital nutrient from the woman through the placenta during pregnancy and in breast milk after birth.[45]
Several micronutrients are important for the health of the developing fetus, especially in areas of the world where insufficient nutrition is prevalent.[46] In developed areas, such as Western Europe and the United States, certain nutrients such as Vitamin D and calcium, required for bone development, may require supplementation.[47][48][49]
Dangerous bacteria or parasites may contaminate foods, particularly Listeria and toxoplasma, toxoplasmosis agent. Careful washing of fruits and raw vegetables may remove these pathogens, as may thoroughly cooking leftovers, meat, or processed meat. Soft cheeses may contain Listeria; if milk is raw, the risk may increase. Cat feces pose a particular risk of toxoplasmosis. Pregnant women are also more prone to Salmonella infections from eggs and poultry, which should be thoroughly cooked. Practicing good hygiene in the kitchen can reduce these risks.[50]
Weight gain
Caloric intake must be increased to ensure proper development of the fetus. The amount of weight gained during pregnancy varies among women. The National Health Service recommends that overall weight gain during the 9 month period for women who start pregnancy with normal weight be 10 to 12.5 kilograms (22–28 lb).[51] During pregnancy, insufficient weight gain can compromise the health of the fetus. Likewise, excessive weight gain can pose risks to the woman and the fetus. Women who are prone to being overweight may choose to plan a healthy diet and exercise to help moderate the amount of weight gained.Immune tolerance
The fetus inside a pregnant woman may be viewed as an unusually successful allograft, since it genetically differs from the woman.[52] In the same way, many cases of spontaneous abortion may be described in the same way as maternal transplant rejection.[52]
Medication use
Drugs used during pregnancy can have temporary or permanent effects on the fetus. Therefore many physicians would prefer not to prescribe for pregnant women, the major concern being over teratogenicity of the drugs.
Drugs have been classified into categories A,B,C,D and X based on the Food and Drug Administration (FDA) rating system to provide therapeutic guidance based on potential benefits and fetal risks. Drugs like multivitamins that have demonstrated no fetal risks after controlled studies in humans are classified as Category A. On the other hand drugs like thalidomide with proven fetal risks that outweigh all benefits are classified as Category X.[53]
Exposure to toxins
Various toxins pose a significant hazard to fetuses during development:
- Alcohol ingestion during pregnancy may cause fetal alcohol syndrome, a permanent and often devastating birth-defect syndrome. A number of studies have shown that light to moderate drinking during pregnancy might not pose a risk to the fetus, although no amount of alcohol during pregnancy can be guaranteed to be absolutely safe.[54][55][56]
- Women who have suffered mercury poisoning in pregnancy have sometimes given birth to children with serious birth defects, termed Minamata disease.
Sexual activity during pregnancy
Most pregnant women can enjoy sexual activity during pregnancy throughout gravidity. Most research suggests that, during pregnancy, both sexual desire and frequency of sexual relations decrease.[57][58] In context of this overall decrease in desire, some studies indicate a second-trimester increase, preceding a decrease.[59] However, these decreases are not universal: a significant number of women report greater sexual satisfaction throughout their pregnancies.[60]
Abortion
An abortion is termination of the fetus either naturally or via medical methods. Natural abortion (miscarriage) is rare more than two months after fertilization.[29]
Stem cell collection
Two different types of stem cells can be collected before childbirth: amniotic stem cells and umbilical cord blood stem cells. The collection of amniotic stem cells is part of the process of amniocentesis. Umbilical cord blood stem cells can be stored in both public and private banks, such as the Biocell Center in Boston.[61][62][63].
Complications and complaints
Each year, according to the WHO, ill-health as a result of pregnancy is experienced (sometimes permanently) by more than 20 million women around the world. Furthermore, the “lives of eight million women are threatened, and more than 500,000 women are estimated to have died in 1995 as a result of causes related to pregnancy and childbirth”.[64]
The following are complaints that may occur during pregnancy:
- Back pain. A particularly common complaint in the third trimester when the patient’s center of gravity has shifted.
- Carpal tunnel syndrome in between an estimated 21% to 62% of cases, possibly due to edema.[65]
- Constipation. A complaint that is caused by decreased bowel motility secondary to elevated progesterone (normal in pregnancy), which can lead to greater absorption of water.
- Braxton Hicks contractions. Occasional, irregular, and often painless contractions that occur several times per day.
- Edema (swelling). Common complaint in advancing pregnancy. Caused by compression of the inferior vena cava (IVC) and pelvic veins by the uterus leads to increased hydrostatic pressure in lower extremities.
- Regurgitation, heartburn, and nausea. Common complaints that may be caused by Gastroesophageal Reflux Disease (GERD); this is determined by relaxation of the lower esophageal sphincter (LES) and increased transit time in the stomach (normal in pregnancy), as well as by increased intraabdominal pressure, caused by the enlarging uterus.
- Haemorrhoids. Complaint that is often noted in advancing pregnancy. Caused by increased venous stasis and IVC compression leading to congestion in venous system, along with increased abdominal pressure secondary to the pregnant space-occupying uterus and constipation.
- Pelvic girdle pain. PGP disorder is complex and multi-factorial and likely to be represented by a series of sub-groups with different underlying pain drivers from peripheral or central nervous system,[66] altered laxity/stiffness of muscles,[67] laxity to injury of tendinous/ligamentous structures[68] to ‘mal-adaptive’ body mechanics.[69] Musculo-Skeletal Mechanics involved in gait and weightbearing activities can be mild to grossly impaired. PGP can begin peri or postpartum. There is pain, instability or dysfunction in the symphysis pubis and/or sacroiliac joints.
- Round Ligament Pain. Pain experienced when the ligaments positioned under the uterus stretch and expand to support the woman’s growing uterus
- Increased urinary frequency. A common complaint referred by the gravida, caused by increased intravascular volume, elevated GFR (glomerular filtration rate), and compression of the bladder by the expanding uterus.
- Varicose veins. Common complaint caused by relaxation of the venous smooth muscle and increased intravascular pressure.
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