pregnancy pregnancy pregnancy is the time during which one or more offspring develops (gestates) inside a woman's uterus (womb). a multiple pregnancy involves more than one offspring, such as with twins. pregnancyother namesgestationa woman in the third trimester of pregnancyspecialtyobstetrics, midwiferysymptomsmissed periods, tender breasts, nausea and vomiting, hunger, frequent urinationcomplicationsmiscarriage, high blood pressure of pregnancy, gestational diabetes, iron-deficiency anemia, severe nausea and vomitingduration~40 weeks from the last menstrual period (38 weeks after conception)causessexual intercourse, assisted reproductive technologydiagnostic methodpregnancy testpreventionbirth control (including emergency contraception)treatmentprenatal care, abortionmedicationfolic acid, iron supplementsfrequency213 million (2012)deaths 230,600 (2016) pregnancy usually occurs by sexual intercourse, but can also occur through assisted reproductive technology procedures. a pregnancy may end in a live birth, a miscarriage, an induced abortion, or a stillbirth. childbirth typically occurs around 40 weeks from the start of the last menstrual period (lmp), a span known as the gestational age. this is just over nine months. counting by fertilization age, the length is about 38 weeks. pregnancy is "the presence of an implanted human embryo or fetus in the uterus"; implantation occurs on average 8–9 days after fertilization. an embryo is the term for the developing offspring during the first seven weeks following implantation (i.e. ten weeks' gestational age), after which the term fetus is used until birth. signs and symptoms of early pregnancy may include missed periods, tender breasts, morning sickness (nausea and vomiting), hunger, implantation bleeding, and frequent urination. pregnancy may be confirmed with a pregnancy test. methods of birth control—or, more accurately, contraception—are used to avoid pregnancy. pregnancy is divided into three trimesters of approximately three months each. the first trimester 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. 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, though babies born at this time will likely experience serious health complications such as heart and respiratory problems and long-term intellectual and developmental disabilities. prenatal care improves pregnancy outcomes. nutrition during pregnancy is important to ensure healthy growth of the fetus. prenatal care may also include avoiding recreational drugs (including tobacco and alcohol), taking regular exercise, having blood tests, and regular physical examinations. complications of pregnancy may include disorders of high blood pressure, gestational diabetes, iron-deficiency anemia, and severe nausea and vomiting. in the ideal childbirth, labor begins on its own "at term". babies born before 37 weeks are "preterm" and at higher risk of health problems such as cerebral palsy. babies born between weeks 37 and 39 are considered "early term" while those born between weeks 39 and 41 are considered "full term". babies born between weeks 41 and 42 weeks are considered "late term" while after 42 weeks they are considered "post term". delivery before 39 weeks by labor induction or caesarean section is not recommended unless required for other medical reasons. about 213 million pregnancies occurred in 2012, of which, 190 million (89%) were in the developing world and 23 million (11%) were in the developed world. the number of pregnancies in women aged between 15 and 44 is 133 per 1,000 women. about 10% to 15% of recognized pregnancies end in miscarriage. in 2016, complications of pregnancy resulted in 230,600 maternal deaths, down from 377,000 deaths in 1990. common causes include bleeding, infections, hypertensive diseases of pregnancy, obstructed labor, miscarriage, abortion, or ectopic pregnancy. globally, 44% of pregnancies are unplanned. over half (56%) of unplanned pregnancies are aborted. among unintended pregnancies in the united states, 60% of the women used birth control to some extent during the month pregnancy began. terminology 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. women who have never carried a pregnancy more than 20 weeks 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 main article: signs and symptoms of pregnancy further information: complications of pregnancy melasma: pigment changes to the face due to pregnancyin the later part of pregnancy the uterus takes up much of the abdomen. the usual signs and symptoms of pregnancy do not significantly interfere with activities of daily living or pose a health-threat to the mother or baby. however, pregnancy complications can cause other more severe symptoms, such as those associated with anemia. common signs and symptoms of pregnancy include: tiredness morning sickness constipation pelvic girdle pain back pain braxton hicks contractions. occasional, irregular, and often painless contractions that occur several times per day. peripheral edema swelling of the lower limbs. common complaint in advancing pregnancy. can be caused by inferior vena cava syndrome resulting from compression of the inferior vena cava and pelvic veins by the uterus leading to increased hydrostatic pressure in lower extremities. low blood pressure often caused by compression of both the inferior vena cava and the abdominal aorta (aortocaval compression syndrome). increased urinary frequency. a common complaint, caused by increased intravascular volume, elevated glomerular filtration rate, and compression of the bladder by the expanding uterus. urinary tract infection varicose veins. common complaint caused by relaxation of the venous smooth muscle and increased intravascular pressure. hemorrhoids (piles). swollen veins at or inside the anal area. caused by impaired venous return, straining associated with constipation, or increased intra-abdominal pressure in later pregnancy. regurgitation, heartburn, and nausea. stretch marks 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. timeline comparison of dating systems for a typical pregnancy event gestational age (from the start of the last menstrual period) fertilization age implantation age menstrual period begins day 1 of pregnancy not pregnant not pregnant has sex and ovulates 2 weeks pregnant not pregnant not pregnant fertilization; cleavage stage begins day 15 day 1 not pregnant implantation of blastocyst begins day 20 day 6 day 0 implantation finished day 26 day 12 day 6 (or day 0) embryo stage begins; also, first missed period 4 weeks day 15 day 9 primitive heart function can be detected 5 weeks, 5 days day 26 day 20 fetal stage begins 10 weeks, 1 day 8 weeks, 1 day 7 weeks, 2 days first trimester ends 13 weeks 11 weeks 10 weeks second trimester ends 26 weeks 24 weeks 23 weeks childbirth 39–40 weeks 37–38 weeks: 108 36–37 weeks 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. this model means that the woman is counted as being "pregnant" two weeks before conception and three weeks before implantation. sometimes, timing may also use the fertilization age, which is the age of the embryo since conception. start of gestational age main article: gestational age the american congress of obstetricians and gynecologists recommend the following methods to calculate gestational age: directly calculating the days since the beginning of the last menstrual period. 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. in case of in vitro fertilization, calculating days since oocyte retrieval or co-incubation and adding 14 days. trimesters pregnancy is divided into three trimesters, each lasting for approximately three months. the first trimester begins with the start of gestational age as described above, that is, the beginning of week 1, or 0 weeks + 0 days of gestational age (ga). it ends at week 12 (11 weeks + 6 days of ga) or end of week 14 (13 weeks + 6 days of ga). the second trimester is defined as starting, between the beginning of week 13 (12 weeks +0 days of ga) and beginning of week 15 (14 weeks + 0 days of ga). it ends at the end of week 27 (26 weeks + 6 days of ga) or end of week 28 (27 weeks + 6 days of ga). the third trimester is defined as starting, between the beginning of week 28 (27 weeks + 0 days of ga) or beginning of week 29 (28 weeks + 0 days of ga). it lasts until childbirth. timeline of pregnancy, including (from top to bottom): trimesters, embryo/fetus development, gestational age in weeks and months, viability and maturity stages estimation of due date 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. main article: estimated date of delivery 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. the american college of obstetricians and gynecologists divides full term into three divisions: early-term: 37 weeks and 0 days through 38 weeks and 6 days full-term: 39 weeks and 0 days through 40 weeks and 6 days late-term: 41 weeks and 0 days through 41 weeks and 6 days post-term: greater than or equal to 42 weeks and 0 days 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