Pregnancy (latin "graviditas") 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.
One scientific term for the state of pregnancy is gravid , and a pregnant female is sometimes referred to as a gravida . 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", and a woman in subsequent pregnancies as a multigravida or "multiparous". 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".
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.
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.
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 an 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 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.
Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.
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.
The expected date of delivery (EDD) is 40 weeks counting from the last menstrual period (LMP), and birth usually occurs between 37 and 42 weeks. 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. When a pregnancy exceeds 42 weeks (294 days), the risk of complications for woman and fetus increases significantly. As such, obstetricians usually prefer to induce labour, in an uncomplicated pregnancy, at some stage between 41 and 42 weeks.
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.
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. 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.
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.
The beginning of pregnancy 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 , 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. 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).
Pregnancy detection can be accomplished using one or more of various pregnancy tests, which detect hormones generated by the newly formed placenta. Clinical blood and urine tests can detect pregnancy 12 days after implantation , which is as early as 6 to 8 days after fertilization. Blood pregnancy tests are mo
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