Pregnancy is divided into three trimesters. The first trimester is from week one through 12 and includes conception, which is when the sperm fertilizes the egg. The fertilized egg then travels down the fallopian tube and attaches to the inside of the uterus, where it begins to form the embryo and placenta. During the first trimester, the possibility of miscarriage (natural death of embryo or fetus) is at its highest. The second trimester is from week 13 through 28. Around the middle of the second trimester, movement of the fetus may be felt. At 28 weeks, more than 90% of babies can survive outside of the uterus if provided with high-quality medical care. The third trimester is from 29 weeks through 40 weeks.
William Hunter, Anatomia uteri humani gravidi tabulis illustrata, 1774
Associated terms for pregnancy are gravid and parous. Gravidus and gravid come from the Latin word meaning "heavy" and a pregnant female is sometimes referred to as a gravida.Gravidity refers to the number of times that a female has been pregnant. Similarly, the term parity is used for the number of times that a female carries a pregnancy to a viable stage. Twins and other multiple births are counted as one pregnancy and birth. 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 is referred to as a primigravida, and a woman in subsequent pregnancies as a multigravida or as multiparous. Therefore, during a second pregnancy a woman would be described as gravida 2, para 1 and upon live delivery as gravida 2, para 2. In-progress pregnancies, abortions, miscarriages and/or stillbirths account for parity values being less than the gravida number. In the case of a multiple birth the gravida number and parity value are increased by one only. Women who have never carried a pregnancy achieving more than 20 weeks of gestation age are referred to as nulliparous.
A pregnancy is considered term at 37 weeks of gestation. It is preterm if less than 37 weeks and postterm at or beyond 42 weeks of gestation. American College of Obstetricians and Gynecologists have recommended further division with early term 37 weeks up to 39 weeks, full term 39 weeks up to 41 weeks, and late term 41 weeks up to 42 weeks. The terms preterm and postterm have largely replaced earlier terms of premature and postmature. Preterm and postterm are defined 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.
Signs and symptoms
Melasma: pigment changes to the face due to pregnancy
Breast tenderness is common during the first trimester, and is more common in women who are pregnant at a young age.
Melasma, also known as the mask of pregnancy, is a discoloration, most often of the face. It usually begins to fade several months after giving birth.
The chronology of pregnancy is, unless otherwise specified, generally given as gestational age, where the starting point is the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Sometimes, timing may also use the fertilization age which is the age of the embryo.
Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods), and using the mean gestational age of other embryos or fetuses of the same size. If the gestational age as calculated from an early ultrasound is contradictory to the one calculated directly from the last menstrual period, it is still the one from the early ultrasound that is used for the rest of the pregnancy.
Distribution of gestational age at childbirth among singleton live births, given both when gestational age is estimated by first trimester ultrasound and directly by last menstrual period. Roughly 80% of births occur between 37 and 41 weeks of gestational age.
Due date estimation basically follows two steps:
Determination of which time point is to be used as origin for gestational age, as described in the section above.
Adding the estimated gestational age at childbirth to the above time point. Childbirth on average occurs at a gestational age of 280 days (40 weeks), which is therefore often used as a standard estimation for individual pregnancies. However, alternative durations as well as more individualized methods have also been suggested.
Naegele's rule is a standard way of calculating the due date for a pregnancy when assuming a gestational age of 280 days at childbirth. The rule estimates the expected date of delivery (EDD) by adding a year, subtracting three months, and adding seven days to the origin of gestational age. Alternatively there are mobile apps, which essentially always give consistent estimations compared to each other and correct for leap year, while pregnancy wheels made of paper can differ from each other by 7 days and generally do not correct for leap year.
Furthermore, actual childbirth has only a certain probability of occurring within the limits of the estimated due date. A study of singleton live births came to the result that childbirth has a standard deviation of 14 days when gestational age is estimated by first trimester ultrasound, and 16 days when estimated directly by last menstrual period.
Fertilization (conception) is sometimes used as the initiation of pregnancy, with the derived age being termed fertilization age. Fertilization usually occurs about two weeks before the next expected menstrual period.
A third point in time is also considered by some people to be the true beginning of a pregnancy: This is time of implantation, when the future fetus attaches to the lining of the uterus. This is about a week to ten days after fertilization.
Development of embryo and fetus
[[File:HumanEmbryogenesis.svg|thumb|The initial stages of human embryogenesis]]
The sperm and the egg cell, which has been released from one of the female's two ovaries, unite in one of the two fallopian tubes. The fertilized egg, known as a zygote, then moves toward the uterus, a journey that can take up to a week to complete. Cell division begins approximately 24 to 36 hours after the female and male cells unite. Cell division continues at a rapid rate and the cells then develop into what is known as a blastocyst. The blastocyst arrives at the uterus and attaches to the uterine wall, a process known as implantation.
The development of the mass of cells that will become the infant is called embryogenesis during the first approximately ten weeks of gestation. During this time, cells begin to differentiate into the various body systems. The basic outlines of the organ, body, and nervous systems are established. By the end of the embryonic stage, the beginnings of features such as fingers, eyes, mouth, and ears become visible. Also during this time, there is development of structures important to the support of the embryo, including the placenta and umbilical cord. The placenta connects the developing embryo to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. The umbilical cord is the connecting cord from the embryo or fetus to the placenta.
After about ten weeks of gestational age, the embryo becomes known as a fetus. At the beginning of the fetal stage, the risk of miscarriage decreases sharply. At this stage, a fetus is about 30 mm (1.2 inches) in length, the heartbeat is seen via ultrasound, and the fetus makes involuntary motions. During continued fetal development, the early body systems, and structures that were established in the embryonic stage continue to develop. Sex organs begin to appear during the third month of gestation. The fetus continues to grow in both weight and length, although the majority of the physical growth occurs in the last weeks of pregnancy.
Electrical brain activity is first detected between the fifth and sixth week of gestation. It is considered primitive neural activity rather than the beginning of conscious thought. Synapses begin forming at 17 weeks, and begin to multiply quickly at week 28 until 3 to 4 months after birth.
Embryo at 4 weeks after fertilization. (Gestational age of 6 weeks.)
Fetus at 8 weeks after fertilization. (Gestational age of 10 weeks.)
Fetus at 18 weeks after fertilization. (Gestational age of 20 weeks.)
Fetus at 38 weeks after fertilization. (Gestational age of 40 weeks.)
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)
Breast changes as seen during pregnancy. The areolae are larger and darker.
The fetus is genetically different from its mother, and can be viewed as an unusually successful allograft. The main reason for this success is increased immune tolerance during pregnancy. Immune tolerance is the concept that the body is able to not mount an immune system response against certain triggers.
Pregnancy is typically broken into three groups of three months, each known as a trimester. Each trimester is defined as 14 weeks, for a total duration of 42 weeks, although the average duration of pregnancy is 40 weeks.
The uterus as it changes in size over the duration of the trimesters
By the end of the second trimester, the expanding uterus has created a visible "baby bump". Although the breasts have been developing internally since the beginning of the pregnancy, most of the visible changes appear after this point.
Weeks 13 to 28 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. 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 during the first trimester, it is not until the second trimester that movement, known 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. It is common for some women not to feel the fetus move until much later. During the second trimester, most women begin to wear maternity clothes.
Pregnant woman in third trimester of pregnancy (last month)
The uterus expands making up a larger and larger portion of the woman's abdomen. At left anterior view with months labeled, at right lateral view labeling the last 4 weeks. During the final stages of gestation before childbirth the fetus and uterus will drop to a lower position.
Final weight gain takes place, which is the most weight gain throughout the pregnancy. The woman's abdomen will transform in shape as it drops due to the fetus turning in a downward position ready for birth. During the second trimester, the woman's abdomen would have been upright, whereas in the third trimester it will drop down low. The fetus moves regularly, and is felt by the woman. Fetal movement can become strong and be disruptive to the woman. The woman's navel will sometimes become convex, "popping" out, due to the expanding abdomen.
Head engagement, where the fetal head descends into cephalic presentation, relieves pressure on the upper abdomen with renewed ease in breathing. It also severely reduces bladder capacity, and increases pressure on the pelvic floor and the rectum.
It is also during the third trimester that maternal activity and sleep positions may affect fetal development due to restricted blood flow. For instance, the enlarged uterus may impede blood flow by compressing the vena cava when lying flat, which is relieved by lying on the left side.
Childbirth, referred to as labor and delivery in the medical field, is the process whereby an infant is born.
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. Studies show that skin-to-skin contact between a mother and her newborn immediately after birth is beneficial for both the mother and baby. A review done by the World Health Organization found that skin-to-skin contact between mothers and babies after birth reduces crying, improves mother-infant interaction, and helps mothers to breastfeed successfully. They recommend that neonates be allowed to bond with the mother during their first two hours after birth, the period that they tend to be more alert than in the following hours of early life.
In the ideal childbirth labor begins on its own when a woman is "at term".
Events before completion of 37 weeks are considered preterm.Preterm birth is associated with a range of complications and should be avoided if possible.
Sometimes if a woman's water breaks or she has contractions before 39 weeks, birth is unavoidable. However, spontaneous birth after 37 weeks is considered term and is not associated with the same risks of a pre-term birth. Planned birth before 39 weeks by Caesarean section or labor induction, although "at term", results in an increased risk of complications. This is from factors including underdeveloped lungs of newborns, infection due to underdeveloped immune system, feeding problems due to underdeveloped brain, and jaundice from underdeveloped liver.
Babies born between 39 and 41 weeks gestation have better outcomes than babies born either before or after this range. This special time period is called "full term". Whenever possible, waiting for labor to begin on its own in this time period is best for the health of the mother and baby. The decision to perform an induction must be made after weighing the risks and benefits, but is safer after 39 weeks.
Events after 42 weeks are considered postterm. When a pregnancy exceeds 42 weeks, the risk of complications for both the woman and the fetus increases significantly. Therefore, in an otherwise uncomplicated pregnancy, obstetricians usually prefer to induce labour at some stage between 41 and 42 weeks.
The postnatal period, also referred to as the puerperium, begins immediately after delivery and extends for about six weeks. During this period, the mother's body begins the return to pre-pregnancy conditions that includes changes in hormone levels and uterus size.
The beginning of pregnancy may be detected either based on symptoms by the woman herself, or by using pregnancy tests. However, an important condition with serious health implications that is quite common is the denial of pregnancy by the pregnant woman. About one in 475 denials will last until around the 20th week of pregnancy. The proportion of cases of denial, persisting until delivery is about 1 in 2500. Conversely, some non-pregnant women have a very strong belief that they are pregnant along with some of the physical changes. This condition is known as a false pregnancy.
Darkening of the nipples and areolas due to an increase in hormones.
Pregnancy detection can be accomplished using one or more various pregnancy tests, which detect hormones generated by the newly formed placenta, serving as biomarkers of pregnancy. Blood and urine tests can detect pregnancy 12 days after implantation. Blood pregnancy tests are more sensitive than urine tests (giving fewer false negatives). Home pregnancy tests are urine tests, and normally detect a pregnancy 12 to 15 days after fertilization. A quantitative blood test can determine approximately the date the embryo was conceived because HCG doubles every 36 to 48 hours. A single test of progesterone levels can also help determine how likely a fetus will survive in those with a threatened miscarriage (bleeding in early pregnancy).
Flowchart showing the recommended weight limits for lifting at work during pregnancy as a function of lifting frequency, weeks of gestation, and the position of the lifted object relative to the lifter's body.
Pre-conception counseling is care that is provided to a woman and/ or couple to discuss conception, pregnancy, current health issues and recommendations for the period before pregnancy.
Prenatal medical care is the medical and nursing care recommended for women during pregnancy, time intervals and exact goals of each visit differ by country. Women who are high risk have better outcomes if they are seen regularly and frequently by a medical professional than women who are low risk. A woman can be labeled as high risk for different reasons including previous complications in pregnancy, complications in the current pregnancy, current medical diseases, or social issues.
The aim of good prenatal care is prevention, early identification, and treatment of any medical complications. A basic prenatal visit consists of measurement of blood pressure, fundal height, weight and fetal heart rate, checking for symptoms of labor, and guidance for what to expect next.
Nutrition during pregnancy is important to ensure healthy growth of the fetus. Nutrition during pregnancy is different from the non-pregnant state. There are increased energy requirements and specific micronutrient requirements. Women benefit from education to encourage a balanced energy and protein intake during pregnancy. Some women may need professional medical advice if their diet is affected by medical conditions, food allergies, or specific religious/ ethical beliefs.
Adequate periconceptional (time before and right after conception) folic acid (also called folate or Vitamin B9) intake has been shown to decrease the risk of fetal neural tube defects, such as spina bifida. The neural tube develops during the first 28 days of pregnancy, a urine pregnancy test is not usually positive until 14 days post-conception, explaining the necessity to guarantee adequate folate intake before conception. Folate is abundant in green leafy vegetables, legumes, and citrus. In the United States and Canada, most wheat products (flour, noodles) are fortified with folic acid.
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.
Several micronutrients are important for the health of the developing fetus, especially in areas of the world where insufficient nutrition is common. Women living in low and middle income countries are suggested to take multiple micronutrient supplements containing iron and folic acid. These supplements have been shown to improve birth outcomes in developing countries, but do not have an effect on perinatal mortality. Adequate intake of folic acid, and iron is often recommended. In developed areas, such as Western Europe and the United States, certain nutrients such as Vitamin D and calcium, required for bone development, may also require supplementation. Vitamin E supplementation has not been shown to improve birth outcomes. Zinc supplementation has been associated with a decrease in preterm birth, but it is unclear whether it is causative. Daily iron supplementation reduces the risk of maternal anemia. Studies of routine daily iron supplementation for pregnant women found improvement in blood iron levels, without a clear clinical benefit. The nutritional needs for women carrying twins or triplets are higher than those of women carrying one baby.
Women are counseled to avoid certain foods, because of the possibility of contamination with bacteria or parasites that can cause illness. Careful washing of fruits and raw vegetables may remove these pathogens, as may thoroughly cooking leftovers, meat, or processed meat. Unpasteurized dairy and deli meats may contain Listeria, which can cause neonatal meningitis, stillbirth and miscarriage. Pregnant women are also more prone to Salmonella infections, can be in eggs and poultry, which should be thoroughly cooked. Cat feces and undercooked meats may contain the parasite Toxoplasma gondii and can cause toxoplasmosis. Practicing good hygiene in the kitchen can reduce these risks.
Women are also counseled to eat seafood in moderation and to eliminate seafood known to be high in mercury because of the risk of birth defects. Pregnant women are counseled to consume caffeine in moderation, because large amounts of caffeine are associated with miscarriage. However, the relationship between caffeine, birthweight, and preterm birth is unclear.
The amount of healthy weight gain during a pregnancy varies. Weight gain is related to the weight of the baby, the placenta, extra circulatory fluid, larger tissues, and fat and protein stores. Most needed weight gain occurs later in pregnancy.
The Institute of Medicine recommends an overall pregnancy weight gain for those of normal weight (body mass index of 18.5-24.9), of 11.3-15.9 kg (25-35 pounds) having a singleton pregnancy. Women who are underweight (BMI of less than 18.5), should gain between 12.7-18 kg (28-40 lbs), while those who are overweight (BMI of 25-29.9) are advised to gain between 6.8-11.3 kg (15-25 lbs) and those who are obese (BMI>30) should gain between 5-9 kg (11-20 lbs). These values reference the expectations for a term pregnancy.
Around 50% of women of childbearing age in developed countries like the United Kingdom are overweight or obese before pregnancy. Diet modification is the most effective way to reduce weight gain and associated risks in pregnancy.
Drugs used during pregnancy can have temporary or permanent effects on the fetus. Anything (including drugs) that can cause permanent deformities in the fetus are labeled as teratogens. In the U.S., drugs were 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, including some 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.
Ethanol during pregnancy can cause one or more fetal alcohol spectrum disorders. According to the CDC, there is no known safe amount of alcohol during pregnancy and no safe time to drink during pregnancy, including before a woman knows that she is pregnant.
Pregnant women can also be exposed to toxins in the workplace, including airborne particles. The effects of wearing N95 filtering facepiece respirators are similar for pregnant women as for non-pregnant women, and wearing a respirator for one hour does not affect the fetal heart rate.
Most women can continue to engage in sexual activity throughout pregnancy. Most research suggests that during pregnancy both sexual desire and frequency of sexual relations decrease. In context of this overall decrease in desire, some studies indicate a second-trimester increase, preceding a decrease during the third trimester.
Sex during pregnancy is a low-risk behavior except when the healthcare provider advises that sexual intercourse be avoided for particular medical reasons. For a healthy pregnant woman, there is no safe or right way to have sex during pregnancy. Pregnancy alters the vaginal flora with a reduction in microscopic species/genus diversity.
The Clinical Practice Obstetrics Committee of Canada recommends that "All women without contraindications should be encouraged to participate in aerobic and strength-conditioning exercises as part of a healthy lifestyle during their pregnancy". Although an upper level of safe exercise intensity has not been established, women who were regular exercisers before pregnancy and who have uncomplicated pregnancies should be able to engage in high intensity exercise programs. In general, participation in a wide range of recreational activities appears to be safe, with the avoidance of those with a high risk of falling such as horseback riding or skiing or those that carry a risk of abdominal trauma, such as soccer or hockey.
The American College of Obstetricians and Gynecologists reports that in the past, the main concerns of exercise in pregnancy were focused on the fetus and any potential maternal benefit was thought to be offset by potential risks to the fetus. However, they write that more recent information suggests that in the uncomplicated pregnancy, fetal injuries are highly unlikely. They do, however, list several circumstances when a woman should contact her health care provider before continuing with an exercise program: vaginal bleeding, dyspnea before exertion, dizziness, headache, chest pain, muscle weakness, preterm labor, decreased fetal movement, amniotic fluid leakage, and calf pain or swelling (to rule out thrombophlebitis).
It has been suggested that shift work and exposure to bright light at night should be avoided at least during the last trimester of pregnancy to decrease the risk of psychological and behavioral problems in the newborn.
In low risk pregnancies, most health care providers approve flying until about 36 weeks of gestational age. Most airlines allow pregnant women to fly short distances at less than 36 weeks, and long distances at less than 32 weeks. Many airlines require a doctor's note that approves flying, specially at over 28 weeks. During flights, the risk of deep vein thrombosis is decreased by getting up and walking occasionally, as well as by avoiding dehydration.
Thyroid disease in pregnancy can, if uncorrected, cause adverse effects on fetal and maternal well-being. The deleterious effects of thyroid dysfunction can also extend beyond pregnancy and delivery to affect neurointellectual development in the early life of the child. Demand for thyroid hormones is increased during pregnancy, which may cause a previously unnoticed thyroid disorder to worsen.
About 213 million pregnancies occurred in 2012 of which 190 million were in the developing world and 23 million were in the developed world. This is about 133 pregnancies per 1,000 women between the ages of 15 and 44. About 10% to 15% of recognized pregnancies end in miscarriage. Globally, 44% of pregnancies are unplanned. Over half (56%) of unplanned pregnancies are aborted. In countries where abortion is prohibited, or only carried out in circumstances where the mother's life is at risk, 48% of unplanned pregnancies are aborted illegally. Compared to the rate in countries where abortion is legal, at 69%.
Of pregnancies in 2012, 120 million occurred in Asia, 54 million in Africa, 19 million in Europe, 18 million in Latin America and the Caribbean, 7 million in North America, and 1 million in Oceania. Pregnancy rates are 140 per 1000 women of childbearing age in the developing world and 94 per 1000 in the developed world.
The rate of pregnancy, as well as the ages at which it occurs, differ by country and region. It is influenced by a number of factors, such as cultural, social and religious norms; access to contraception; and rates of education. The total fertility rate (TFR) in 2013 was estimated to be highest in Niger (7.03 children/woman) and lowest in Singapore (0.79 children/woman).
In Europe, the average childbearing age has been rising continuously for some time. In Western, Northern, and Southern Europe, first-time mothers are on average 26 to 29 years old, up from 23 to 25 years at the start of the 1970s. In a number of European countries (Spain), the mean age of women at first childbirth has crossed the 30-year threshold.
This process is not restricted to Europe. Asia, Japan and the United States are all seeing average age at first birth on the rise, and increasingly the process is spreading to countries in the developing world like China, Turkey and Iran. In the US, the average age of first childbirth was 25.4 in 2010.
In most cultures, pregnant women have a special status in society and receive particularly gentle care. At the same time, they are subject to expectations that may exert great psychological pressure, such as having to produce a son and heir. In many traditional societies, pregnancy must be preceded by marriage, on pain of ostracism of mother and (illegitimate) child.
Overall, pregnancy is accompanied by numerous customs that are often subject to ethnological research, often rooted in traditional medicine or religion. The baby shower is an example of a modern custom.
Pregnancy is an important topic in sociology of the family. The prospective child may preliminarily be placed into numerous social roles. The parents' relationship and the relation between parents and their surroundings are also affected.
A belly cast may be made during pregnancy as a keepsake.
Images of pregnant women, especially small figurines, were made in traditional cultures in many places and periods, though it is rarely one of the most common types of image. These include ceramic figures from some Pre-Columbian cultures, and a few figures from most of the ancient Mediterranean cultures. Many of these seem to be connected with fertility. Identifying whether such figures are actually meant to show pregnancy is often a problem, as well as understanding their role in the culture concerned.
Among the oldest surviving examples of the depiction of pregnancy are prehistoric figurines found across much of Eurasia and collectively known as Venus figurines. Some of these appear to be pregnant.
The unhappy scene usually called Diana and Callisto, showing the moment of discovery of Callisto's forbidden pregnancy, is sometimes painted from the Renaissance onwards. Gradually, portraits of pregnant women began to appear, with a particular fashion for "pregnancy portraits" in elite portraiture of the years around 1600.
Pregnancy, and especially pregnancy of unmarried women, is also an important motif in literature. Notable examples include Hardy's Tess of the d'Urbervilles and Goethe's Faust.
An abortion is the termination of an embryo or fetus, either naturally or via medical methods. When done electively, it is more often done within the first trimester than the second, and rarely in the third. Not using contraception, contraceptive failure, poor family planning or rape can lead to undesired pregnancies. Legality of socially indicated abortions varies widely both internationally and through time. In most countries of Western Europe, abortions during the first trimester were a criminal offense a few decades ago[when?] but have since been legalized, sometimes subject to mandatory consultations. In Germany, for example, as of 2009 less than 3% of abortions had a medical indication.
Many countries have various legal regulations in place to protect pregnant women and their children. Maternity Protection Convention ensures that pregnant women are exempt from activities such as night shifts or carrying heavy stocks. Maternity leave typically provides paid leave from work during roughly the last trimester of pregnancy and for some time after birth. Notable extreme cases include Norway (8 months with full pay) and the United States (no paid leave at all except in some states). Moreover, many countries have laws against pregnancy discrimination.
In the United States, some actions that result in miscarriage or stillbirth are considered crimes. One law that does so is the federal Unborn Victims of Violence Act. In 2014, the American state of Tennessee passed a law which allows prosecutors to charge a woman with criminal assault if she uses illegal drugs during her pregnancy and her fetus or newborn is considered harmed as a result.
^Tunón K, Eik-Nes SH, Grøttum P, Von Düring V, Kahn JA (January 2000). "Gestational age in pregnancies conceived after in vitro fertilization: a comparison between age assessed from oocyte retrieval, crown-rump length and biparietal diameter". Ultrasound in Obstetrics & Gynecology. 15 (1): 41-46. doi:10.1046/j.1469-0705.2000.00004.x. PMID10776011.
^ abHoffman CS, Messer LC, Mendola P, Savitz DA, Herring AH, Hartmann KE (November 2008). "Comparison of gestational age at birth based on last menstrual period and ultrasound during the first trimester". Paediatric and Perinatal Epidemiology. 22 (6): 587-596. doi:10.1111/j.1365-3016.2008.00965.x. PMID19000297.
^Qasim SM, Callan C, Choe JK (October 1996). "The predictive value of an initial serum beta human chorionic gonadotropin level for pregnancy outcome following in vitro fertilization". Journal of Assisted Reproduction and Genetics. 13 (9): 705-708. doi:10.1007/BF02066422. PMID8947817.
^ abCole LA, Khanlian SA, Sutton JM, Davies S, Rayburn WF (January 2004). "Accuracy of home pregnancy tests at the time of missed menses". American Journal of Obstetrics and Gynecology. 190 (1): 100-105. doi:10.1016/j.ajog.2003.08.043. PMID14749643.
^Nguyen TH, Larsen T, Engholm G, Møller H (July 1999). "Evaluation of ultrasound-estimated date of delivery in 17,450 spontaneous singleton births: do we need to modify Naegele's rule?". Ultrasound in Obstetrics & Gynecology. 14 (1): 23-28. doi:10.1046/j.1469-0705.1999.14010023.x. PMID10461334.
^Pyeritz RE (2014). Current Medical Diagnosis & Treatment 2015. McGraw-Hill.
^MacDonald, Leslie A.; Waters, Thomas R.; Napolitano, Peter G.; Goddard, Donald E.; Ryan, Margaret A.; Nielsen, Peter; Hudock, Stephen D. (2013). "Clinical guidelines for occupational lifting in pregnancy: evidence summary and provisional recommendations". American Journal of Obstetrics and Gynecology. 209 (2): 80-88. doi:10.1016/j.ajog.2013.02.047. ISSN0002-9378. PMID23467051.
^Dowswell T, Carroli G, Duley L, Gates S, Gülmezoglu AM, Khan-Neelofur D, Piaggio G, et al. (American College of Obstetricians Gynecologists Committee on Health Care for Undeserved Women) (July 2015). "Alternative versus standard packages of antenatal care for low-risk pregnancy". The Cochrane Database of Systematic Reviews (7): CD000934. doi:10.1002/14651858.cd000934.pub3. PMID26184394.
^Ota E, Hori H, Mori R, Tobe-Gai R, Farrar D (June 2015). "Antenatal dietary education and supplementation to increase energy and protein intake". The Cochrane Database of Systematic Reviews. 6 (6): CD000032. doi:10.1002/14651858.CD000032.pub3. PMID26031211.
^Klusmann A, Heinrich B, Stöpler H, Gärtner J, Mayatepek E, Von Kries R (November 2005). "A decreasing rate of neural tube defects following the recommendations for periconceptional folic acid supplementation". Acta Paediatrica. 94 (11): 1538-1542. doi:10.1080/08035250500340396. PMID16303691.
^Stevenson RE, Allen WP, Pai GS, Best R, Seaver LH, Dean J, Thompson S (October 2000). "Decline in prevalence of neural tube defects in a high-risk region of the United States". Pediatrics. 106 (4): 677-683. doi:10.1542/peds.106.4.677. PMID11015508.
^Centers for Disease Control Prevention (CDC) (January 2008). "Use of supplements containing folic acid among women of childbearing age--United States, 2007". MMWR. Morbidity and Mortality Weekly Report. 57 (1): 5-8. PMID18185493.
^ abGuesnet P, Alessandri JM (January 2011). "Docosahexaenoic acid (DHA) and the developing central nervous system (CNS) - Implications for dietary recommendations". Biochimie. Bioactive Lipids, Nutrition and Health. 93 (1): 7-12. doi:10.1016/j.biochi.2010.05.005. PMID20478353.
^Theobald HE (2007). "Eating for pregnancy and breast-feeding". The Journal of Family Health Care. 17 (2): 45-49. PMID17476978.
^Basile LA, Taylor SN, Wagner CL, Quinones L, Hollis BW (September 2007). "Neonatal vitamin D status at birth at latitude 32 degrees 72': evidence of deficiency". Journal of Perinatology. 27 (9): 568-571. doi:10.1038/sj.jp.7211796. PMID17625571.
^Kuoppala T, Tuimala R, Parviainen M, Koskinen T, Ala-Houhala M (July 1986). "Serum levels of vitamin D metabolites, calcium, phosphorus, magnesium and alkaline phosphatase in Finnish women throughout pregnancy and in cord serum at delivery". Human Nutrition. Clinical Nutrition. 40 (4): 287-293. PMID3488981.
^Ota E, Mori R, Middleton P, Tobe-Gai R, Mahomed K, Miyazaki C, Bhutta ZA (2 February 2015). "Zinc supplementation for improving pregnancy and infant outcome". Cochrane Database of Systematic Reviews (2): CD000230. doi:10.1002/14651858.cd000230.pub5. PMID25927101.
^Jahanfar S, Jaafar SH (9 June 2015). "Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcomes". Cochrane Database of Systematic Reviews (6): CD006965. doi:10.1002/14651858.cd006965.pub4. PMID26058966.
^ abcViswanathan M, Siega-Riz AM, Moos MK, et al. (May 2008). Outcomes of Maternal Weight Gain. Evidence Reports/Technology Assessments, No. 168. Agency for Healthcare Research and Quality. Archived from the original on 28 May 2013. Retrieved 2013.
^ abcInstitute for Quality and Efficiency in Health Care. "Weight gain in pregnancy". Fact sheet. Institute for Quality and Efficiency in Health Care. Archived from the original on 14 December 2013. Retrieved 2013.
^Domenjoz I, Kayser B, Boulvain M (October 2014). "Effect of physical activity during pregnancy on mode of delivery". American Journal of Obstetrics and Gynecology. 211 (4): 401.e1-411. doi:10.1016/j.ajog.2014.03.030. PMID24631706.
^ abDavies GA, Wolfe LA, Mottola MF, MacKinnon C, Arsenault MY, Bartellas E, Cargill Y, Gleason T, Iglesias S, Klein M, Martel MJ, Roggensack A, Wilson K, Gardiner P, Graham T, Haennel R, Hughson R, MacDougall D, McDermott J, Ross R, Tiidus P, Trudeau F (June 2003). "Exercise in pregnancy and the postpartum period". Journal of Obstetrics and Gynaecology Canada. 25 (6): 516-529. doi:10.1016/s1701-2163(16)30313-9. PMID12806453.
^Reiter RJ, Tan DX, Korkmaz A, Rosales-Corral SA (2014). "Melatonin and stable circadian rhythms optimize maternal, placental and fetal physiology". Human Reproduction Update. 20 (2): 293-307. doi:10.1093/humupd/dmt054. PMID24132226.
^ abLeveno K (2013). "52". Williams manual of pregnancy complications. New York: McGraw-Hill Medical. pp. 323-334. ISBN978-0-07-176562-6.
^Tersigni C, Castellani R, de Waure C, Fattorossi A, De Spirito M, Gasbarrini A, Scambia G, Di Simone N (2014). "Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms". Human Reproduction Update. 20 (4): 582-593. doi:10.1093/humupd/dmu007. PMID24619876.
^Saccone G, Berghella V, Sarno L, Maruotti GM, Cetin I, Greco L, Khashan AS, McCarthy F, Martinelli D, Fortunato F, Martinelli P (February 2016). "Celiac disease and obstetric complications: a systematic review and metaanalysis". American Journal of Obstetrics and Gynecology. 214 (2): 225-234. doi:10.1016/j.ajog.2015.09.080. PMID26432464.