Maternal Age: The age of the mother in PREGNANCY.Pregnancy: The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.Paternal Age: Age of the biological father.Down Syndrome: A chromosome disorder associated either with an extra chromosome 21 or an effective trisomy for chromosome 21. Clinical manifestations include hypotonia, short stature, brachycephaly, upslanting palpebral fissures, epicanthus, Brushfield spots on the iris, protruding tongue, small ears, short, broad hands, fifth finger clinodactyly, Simian crease, and moderate to severe INTELLECTUAL DISABILITY. Cardiac and gastrointestinal malformations, a marked increase in the incidence of LEUKEMIA, and the early onset of ALZHEIMER DISEASE are also associated with this condition. Pathologic features include the development of NEUROFIBRILLARY TANGLES in neurons and the deposition of AMYLOID BETA-PROTEIN, similar to the pathology of ALZHEIMER DISEASE. (Menkes, Textbook of Child Neurology, 5th ed, p213)Birth Order: The sequence in which children are born into the family.Pregnancy, High-Risk: Pregnancy in which the mother and/or FETUS are at greater than normal risk of MORBIDITY or MORTALITY. Causes include inadequate PRENATAL CARE, previous obstetrical history (ABORTION, SPONTANEOUS), pre-existing maternal disease, pregnancy-induced disease (GESTATIONAL HYPERTENSION), and MULTIPLE PREGNANCY, as well as advanced maternal age above 35.Infant, Newborn: An infant during the first month after birth.Amniocentesis: Percutaneous transabdominal puncture of the uterus during pregnancy to obtain amniotic fluid. It is commonly used for fetal karyotype determination in order to diagnose abnormal fetal conditions.Parity: The number of offspring a female has borne. It is contrasted with GRAVIDITY, which refers to the number of pregnancies, regardless of outcome.Pregnancy Outcome: Results of conception and ensuing pregnancy, including LIVE BIRTH; STILLBIRTH; SPONTANEOUS ABORTION; INDUCED ABORTION. The outcome may follow natural or artificial insemination or any of the various ASSISTED REPRODUCTIVE TECHNIQUES, such as EMBRYO TRANSFER or FERTILIZATION IN VITRO.Birth Weight: The mass or quantity of heaviness of an individual at BIRTH. It is expressed by units of pounds or kilograms.Gestational Age: The age of the conceptus, beginning from the time of FERTILIZATION. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last MENSTRUATION which is about 2 weeks before OVULATION and fertilization.Prenatal Diagnosis: Determination of the nature of a pathological condition or disease in the postimplantation EMBRYO; FETUS; or pregnant female before birth.Trisomy: The possession of a third chromosome of any one type in an otherwise diploid cell.Pregnancy Trimester, First: The beginning third of a human PREGNANCY, from the first day of the last normal menstrual period (MENSTRUATION) through the completion of 14 weeks (98 days) of gestation.Pregnancy Complications: Conditions or pathological processes associated with pregnancy. They can occur during or after pregnancy, and range from minor discomforts to serious diseases that require medical interventions. They include diseases in pregnant females, and pregnancies in females with diseases.Congenital Abnormalities: Malformations of organs or body parts during development in utero.Nondisjunction, Genetic: The failure of homologous CHROMOSOMES or CHROMATIDS to segregate during MITOSIS or MEIOSIS with the result that one daughter cell has both of a pair of parental chromosomes or chromatids and the other has none.Abortion, Spontaneous: Expulsion of the product of FERTILIZATION before completing the term of GESTATION and without deliberate interference.Birth Certificates: Official certifications by a physician recording the individual's birth date, place of birth, parentage and other required identifying data which are filed with the local registrar of vital statistics.Crown-Rump Length: In utero measurement corresponding to the sitting height (crown to rump) of the fetus. Length is considered a more accurate criterion of the age of the fetus than is the weight. The average crown-rump length of the fetus at term is 36 cm. (From Williams Obstetrics, 18th ed, p91)Nuchal Translucency Measurement: A prenatal ultrasonography measurement of the soft tissue behind the fetal neck. Either the translucent area below the skin in the back of the fetal neck (nuchal translucency) or the distance between occipital bone to the outer skin line (nuchal fold) is measured.Aneuploidy: The chromosomal constitution of cells which deviate from the normal by the addition or subtraction of CHROMOSOMES, chromosome pairs, or chromosome fragments. In a normally diploid cell (DIPLOIDY) the loss of a chromosome pair is termed nullisomy (symbol: 2N-2), the loss of a single chromosome is MONOSOMY (symbol: 2N-1), the addition of a chromosome pair is tetrasomy (symbol: 2N+2), the addition of a single chromosome is TRISOMY (symbol: 2N+1).Chromosome Disorders: Clinical conditions caused by an abnormal chromosome constitution in which there is extra or missing chromosome material (either a whole chromosome or a chromosome segment). (from Thompson et al., Genetics in Medicine, 5th ed, p429)Risk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Cesarean Section: Extraction of the FETUS by means of abdominal HYSTEROTOMY.Pregnancy Trimester, Second: The middle third of a human PREGNANCY, from the beginning of the 15th through the 28th completed week (99 to 196 days) of gestation.Infant, Low Birth Weight: An infant having a birth weight of 2500 gm. (5.5 lb.) or less but INFANT, VERY LOW BIRTH WEIGHT is available for infants having a birth weight of 1500 grams (3.3 lb.) or less.Ultrasonography, Prenatal: The visualization of tissues during pregnancy through recording of the echoes of ultrasonic waves directed into the body. The procedure may be applied with reference to the mother or the fetus and with reference to organs or the detection of maternal or fetal disease.Infant Mortality: Postnatal deaths from BIRTH to 365 days after birth in a given population. Postneonatal mortality represents deaths between 28 days and 365 days after birth (as defined by National Center for Health Statistics). Neonatal mortality represents deaths from birth to 27 days after birth.Chorionic Gonadotropin, beta Subunit, Human: The beta subunit of human CHORIONIC GONADOTROPIN. Its structure is similar to the beta subunit of LUTEINIZING HORMONE, except for the additional 30 amino acids at the carboxy end with the associated carbohydrate residues. HCG-beta is used as a diagnostic marker for early detection of pregnancy, spontaneous abortion (ABORTION, SPONTANEOUS); ECTOPIC PREGNANCY; HYDATIDIFORM MOLE; CHORIOCARCINOMA; or DOWN SYNDROME.Pregnancy, Multiple: The condition of carrying two or more FETUSES simultaneously.Fetal Death: Death of the developing young in utero. BIRTH of a dead FETUS is STILLBIRTH.Premature Birth: CHILDBIRTH before 37 weeks of PREGNANCY (259 days from the first day of the mother's last menstrual period, or 245 days after FERTILIZATION).Mothers: Female parents, human or animal.Pregnancy-Associated Plasma Protein-A: A product of the PLACENTA, and DECIDUA, secreted into the maternal circulation during PREGNANCY. It has been identified as an IGF binding protein (IGFBP)-4 protease that proteolyzes IGFBP-4 and thus increases IGF bioavailability. It is found also in human FIBROBLASTS, ovarian FOLLICULAR FLUID, and GRANULOSA CELLS. The enzyme is a heterotetramer of about 500-kDa.Hernia, Umbilical: A HERNIA due to an imperfect closure or weakness of the umbilical ring. It appears as a skin-covered protrusion at the UMBILICUS during crying, coughing, or straining. The hernia generally consists of OMENTUM or SMALL INTESTINE. The vast majority of umbilical hernias are congenital but can be acquired due to severe abdominal distention.Gastroschisis: A congenital defect with major fissure in the ABDOMINAL WALL lateral to, but not at, the UMBILICUS. This results in the extrusion of VISCERA. Unlike OMPHALOCELE, herniated structures in gastroschisis are not covered by a sac or PERITONEUM.Preimplantation Diagnosis: Determination of the nature of a pathological condition or disease in the OVUM; ZYGOTE; or BLASTOCYST prior to implantation. CYTOGENETIC ANALYSIS is performed to determine the presence or absence of genetic disease.Prenatal Care: Care provided the pregnant woman in order to prevent complications, and decrease the incidence of maternal and prenatal mortality.Fertilization in Vitro: An assisted reproductive technique that includes the direct handling and manipulation of oocytes and sperm to achieve fertilization in vitro.Live Birth: The event that a FETUS is born alive with heartbeats or RESPIRATION regardless of GESTATIONAL AGE. Such liveborn is called a newborn infant (INFANT, NEWBORN).Stillbirth: The event that a FETUS is born dead or stillborn.Perinatal Mortality: Deaths occurring from the 28th week of GESTATION to the 28th day after birth in a given population.Birth Intervals: The lengths of intervals between births to women in the population.Reproductive Techniques, Assisted: Clinical and laboratory techniques used to enhance fertility in humans and animals.Infant, Small for Gestational Age: An infant having a birth weight lower than expected for its gestational age.Fetal Diseases: Pathophysiological conditions of the FETUS in the UTERUS. Some fetal diseases may be treated with FETAL THERAPIES.Abortion, Eugenic: Abortion performed because of possible fetal defects.Pregnancy in Adolescence: Pregnancy in human adolescent females under the age of 19.Chromosome Aberrations: Abnormal number or structure of chromosomes. Chromosome aberrations may result in CHROMOSOME DISORDERS.Polar Bodies: Minute cells produced during development of an OOCYTE as it undergoes MEIOSIS. A polar body contains one of the nuclei derived from the first or second meiotic CELL DIVISION. Polar bodies have practically no CYTOPLASM. They are eventually discarded by the oocyte. (from King & Stansfield, A Dictionary of Genetics, 4th ed)Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.Delivery, Obstetric: Delivery of the FETUS and PLACENTA under the care of an obstetrician or a health worker. Obstetric deliveries may involve physical, psychological, medical, or surgical interventions.Birth Rate: The number of births in a given population per year or other unit of time.Chromosomes, Human, Pair 21: A specific pair of GROUP G CHROMOSOMES of the human chromosome classification.Chorionic Villi Sampling: A method for diagnosis of fetal diseases by sampling the cells of the placental chorionic villi for DNA analysis, presence of bacteria, concentration of metabolites, etc. The advantage over amniocentesis is that the procedure can be carried out in the first trimester.Obstetric Labor Complications: Medical problems associated with OBSTETRIC LABOR, such as BREECH PRESENTATION; PREMATURE OBSTETRIC LABOR; HEMORRHAGE; or others. These complications can affect the well-being of the mother, the FETUS, or both.Twins: Two individuals derived from two FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother. Twins are either monozygotic (TWINS, MONOZYGOTIC) or dizygotic (TWINS, DIZYGOTIC).Logistic Models: Statistical models which describe the relationship between a qualitative dependent variable (that is, one which can take only certain discrete values, such as the presence or absence of a disease) and an independent variable. A common application is in epidemiology for estimating an individual's risk (probability of a disease) as a function of a given risk factor.Chromosomes, Human, Pair 18: A specific pair of GROUP E CHROMOSOMES of the human chromosome classification.Chromosomes, Human, 21-22 and Y: The short, acrocentric human chromosomes, called group G in the human chromosome classification. This group consists of chromosome pairs 21 and 22 and the Y chromosome.Marital Status: A demographic parameter indicating a person's status with respect to marriage, divorce, widowhood, singleness, etc.Karyotyping: Mapping of the KARYOTYPE of a cell.Odds Ratio: The ratio of two odds. The exposure-odds ratio for case control data is the ratio of the odds in favor of exposure among cases to the odds in favor of exposure among noncases. The disease-odds ratio for a cohort or cross section is the ratio of the odds in favor of disease among the exposed to the odds in favor of disease among the unexposed. The prevalence-odds ratio refers to an odds ratio derived cross-sectionally from studies of prevalent cases.Neck: The part of a human or animal body connecting the HEAD to the rest of the body.Prenatal Exposure Delayed Effects: The consequences of exposing the FETUS in utero to certain factors, such as NUTRITION PHYSIOLOGICAL PHENOMENA; PHYSIOLOGICAL STRESS; DRUGS; RADIATION; and other physical or chemical factors. These consequences are observed later in the offspring after BIRTH.Registries: The systems and processes involved in the establishment, support, management, and operation of registers, e.g., disease registers.Socioeconomic Factors: Social and economic factors that characterize the individual or group within the social structure.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Case-Control Studies: Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.Sex Ratio: The number of males per 100 females.Breast Feeding: The nursing of an infant at the breast.Chromosomes, Human, Pair 13: A specific pair of GROUP D CHROMOSOMES of the human chromosome classification.Maternal Exposure: Exposure of the female parent, human or animal, to potentially harmful chemical, physical, or biological agents in the environment or to environmental factors that may include ionizing radiation, pathogenic organisms, or toxic chemicals that may affect offspring. It includes pre-conception maternal exposure.Obstetric Labor, Premature: Onset of OBSTETRIC LABOR before term (TERM BIRTH) but usually after the FETUS has become viable. In humans, it occurs sometime during the 29th through 38th week of PREGNANCY. TOCOLYSIS inhibits premature labor and can prevent the BIRTH of premature infants (INFANT, PREMATURE).Pre-Eclampsia: A complication of PREGNANCY, characterized by a complex of symptoms including maternal HYPERTENSION and PROTEINURIA with or without pathological EDEMA. Symptoms may range between mild and severe. Pre-eclampsia usually occurs after the 20th week of gestation, but may develop before this time in the presence of trophoblastic disease.Sperm Injections, Intracytoplasmic: An assisted fertilization technique consisting of the microinjection of a single viable sperm into an extracted ovum. It is used principally to overcome low sperm count, low sperm motility, inability of sperm to penetrate the egg, or other conditions related to male infertility (INFERTILITY, MALE).Nasal Bone: Either one of the two small elongated rectangular bones that together form the bridge of the nose.Diabetes, Gestational: Diabetes mellitus induced by PREGNANCY but resolved at the end of pregnancy. It does not include previously diagnosed diabetics who become pregnant (PREGNANCY IN DIABETICS). Gestational diabetes usually develops in late pregnancy when insulin antagonistic hormones peaks leading to INSULIN RESISTANCE; GLUCOSE INTOLERANCE; and HYPERGLYCEMIA.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Educational Status: Educational attainment or level of education of individuals.Embryo Transfer: The transfer of mammalian embryos from an in vivo or in vitro environment to a suitable host to improve pregnancy or gestational outcome in human or animal. In human fertility treatment programs, preimplantation embryos ranging from the 4-cell stage to the blastocyst stage are transferred to the uterine cavity between 3-5 days after FERTILIZATION IN VITRO.Regression Analysis: Procedures for finding the mathematical function which best describes the relationship between a dependent variable and one or more independent variables. In linear regression (see LINEAR MODELS) the relationship is constrained to be a straight line and LEAST-SQUARES ANALYSIS is used to determine the best fit. In logistic regression (see LOGISTIC MODELS) the dependent variable is qualitative rather than continuously variable and LIKELIHOOD FUNCTIONS are used to find the best relationship. In multiple regression, the dependent variable is considered to depend on more than a single independent variable.Risk: The probability that an event will occur. It encompasses a variety of measures of the probability of a generally unfavorable outcome.Abortion, Habitual: Three or more consecutive spontaneous abortions.Gravidity: The number of pregnancies, complete or incomplete, experienced by a female. It is different from PARITY, which is the number of offspring borne. (From Stedman, 26th ed)NorwayFetal Macrosomia: A condition of fetal overgrowth leading to a large-for-gestational-age FETUS. It is defined as BIRTH WEIGHT greater than 4,000 grams or above the 90th percentile for population and sex-specific growth curves. It is commonly seen in GESTATIONAL DIABETES; PROLONGED PREGNANCY; and pregnancies complicated by pre-existing diabetes mellitus.Age Factors: Age as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or the effect of a circumstance. It is used with human or animal concepts but should be differentiated from AGING, a physiological process, and TIME FACTORS which refers only to the passage of time.SicilyPregnancy Trimester, Third: The last third of a human PREGNANCY, from the beginning of the 29th through the 42nd completed week (197 to 294 days) of gestation.Pregnancy, Twin: The condition of carrying TWINS simultaneously.Multiple Birth Offspring: The offspring in multiple pregnancies (PREGNANCY, MULTIPLE): TWINS; TRIPLETS; QUADRUPLETS; QUINTUPLETS; etc.Social Class: A stratum of people with similar position and prestige; includes social stratification. Social class is measured by criteria such as education, occupation, and income.Hypertension, Pregnancy-Induced: A condition in pregnant women with elevated systolic (>140 mm Hg) and diastolic (>90 mm Hg) blood pressure on at least two occasions 6 h apart. HYPERTENSION complicates 8-10% of all pregnancies, generally after 20 weeks of gestation. Gestational hypertension can be divided into several broad categories according to the complexity and associated symptoms, such as EDEMA; PROTEINURIA; SEIZURES; abnormalities in BLOOD COAGULATION and liver functions.DenmarkFetal Growth Retardation: The failure of a FETUS to attain its expected FETAL GROWTH at any GESTATIONAL AGE.Estriol: A hydroxylated metabolite of ESTRADIOL or ESTRONE that has a hydroxyl group at C3, 16-alpha, and 17-beta position. Estriol is a major urinary estrogen. During PREGNANCY, a large amount of estriol is produced by the PLACENTA. Isomers with inversion of the hydroxyl group or groups are called epiestriol.Meiosis: A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells.Perinatal Care: The care of women and a fetus or newborn given before, during, and after delivery from the 28th week of gestation through the 7th day after delivery.Apgar Score: A method, developed by Dr. Virginia Apgar, to evaluate a newborn's adjustment to extrauterine life. Five items - heart rate, respiratory effort, muscle tone, reflex irritability, and color - are evaluated 60 seconds after birth and again five minutes later on a scale from 0-2, 0 being the lowest, 2 being normal. The five numbers are added for the Apgar score. A score of 0-3 represents severe distress, 4-7 indicates moderate distress, and a score of 7-10 predicts an absence of difficulty in adjusting to extrauterine life.Prevalence: The total number of cases of a given disease in a specified population at a designated time. It is differentiated from INCIDENCE, which refers to the number of new cases in the population at a given time.Infertility: Inability to reproduce after a specified period of unprotected intercourse. Reproductive sterility is permanent infertility.Abortion, Induced: Intentional removal of a fetus from the uterus by any of a number of techniques. (POPLINE, 1978)Sudden Infant Death: The abrupt and unexplained death of an apparently healthy infant under one year of age, remaining unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. (Pediatr Pathol 1991 Sep-Oct;11(5):677-84)Triplets: Three individuals derived from three FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.Pregnant Women: Human females who are pregnant, as cultural, psychological, or sociological entities.Parturition: The process of giving birth to one or more offspring.Labor, Induced: Artificially induced UTERINE CONTRACTION. Generally, LABOR, OBSTETRIC is induced with the intent to cause delivery of the fetus and termination of pregnancy.Infant, Premature: A human infant born before 37 weeks of GESTATION.Smoking: Inhaling and exhaling the smoke of burning TOBACCO.Fertility: The capacity to conceive or to induce conception. It may refer to either the male or female.SwedenNew YorkChromosomes, Human, 19-20: The short, metacentric human chromosomes, called group F in the human chromosome classification. This group consists of chromosome pairs 19 and 20.Anencephaly: A malformation of the nervous system caused by failure of the anterior neuropore to close. Infants are born with intact spinal cords, cerebellums, and brainstems, but lack formation of neural structures above this level. The skull is only partially formed but the eyes are usually normal. This condition may be associated with folate deficiency. Affected infants are only capable of primitive (brain stem) reflexes and usually do not survive for more than two weeks. (From Menkes, Textbook of Child Neurology, 5th ed, p247)Sex Chromosome Aberrations: Abnormal number or structure of the SEX CHROMOSOMES. Some sex chromosome aberrations are associated with SEX CHROMOSOME DISORDERS and SEX CHROMOSOME DISORDERS OF SEX DEVELOPMENT.Heart Rate, Fetal: The heart rate of the FETUS. The normal range at term is between 120 and 160 beats per minute.Pregnancy in Diabetics: The state of PREGNANCY in women with DIABETES MELLITUS. This does not include either symptomatic diabetes or GLUCOSE INTOLERANCE induced by pregnancy (DIABETES, GESTATIONAL) which resolves at the end of pregnancy.Family Characteristics: Size and composition of the family.Maternal Mortality: Maternal deaths resulting from complications of pregnancy and childbirth in a given population.Mosaicism: The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from a single ZYGOTE, as opposed to CHIMERISM in which the different cell populations are derived from more than one zygote.Fetal Mortality: Number of fetal deaths with stated or presumed gestation of 20 weeks or more in a given population. Late fetal mortality is death after of 28 weeks or more.Infant Welfare: Organized efforts by communities or organizations to improve the health and well-being of infants.Chromosomes, Human, 13-15: The medium-sized, acrocentric human chromosomes, called group D in the human chromosome classification. This group consists of chromosome pairs 13, 14, and 15.Oocytes: Female germ cells derived from OOGONIA and termed OOCYTES when they enter MEIOSIS. The primary oocytes begin meiosis but are arrested at the diplotene state until OVULATION at PUBERTY to give rise to haploid secondary oocytes or ova (OVUM).Maternal Welfare: Organized efforts by communities or organizations to improve the health and well-being of the mother.European Continental Ancestry Group: Individuals whose ancestral origins are in the continent of Europe.Infertility, Female: Diminished or absent ability of a female to achieve conception.Incidence: The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from PREVALENCE, which refers to all cases, new or old, in the population at a given time.Term Birth: CHILDBIRTH at the end of a normal duration of PREGNANCY, between 37 to 40 weeks of gestation or about 280 days from the first day of the mother's last menstrual period.Maternal Behavior: The behavior patterns associated with or characteristic of a mother.EnglandNepalIllegitimacy: The state of birth outside of wedlock. It may refer to the offspring or the parents.Adult Children: Children who have reached maturity or the legal age of majority.Extraction, Obstetrical: Extraction of the fetus by means of obstetrical instruments.Body Height: The distance from the sole to the crown of the head with body standing on a flat surface and fully extended.Fetus: The unborn young of a viviparous mammal, in the postembryonic period, after the major structures have been outlined. In humans, the unborn young from the end of the eighth week after CONCEPTION until BIRTH, as distinguished from the earlier EMBRYO, MAMMALIAN.Abnormalities, Drug-Induced: Congenital abnormalities caused by medicinal substances or drugs of abuse given to or taken by the mother, or to which she is inadvertently exposed during the manufacture of such substances. The concept excludes abnormalities resulting from exposure to non-medicinal chemicals in the environment.Fetal Development: Morphological and physiological development of FETUSES.Reproductive History: An important aggregate factor in epidemiological studies of women's health. The concept usually includes the number and timing of pregnancies and their outcomes, the incidence of breast feeding, and may include age of menarche and menopause, regularity of menstruation, fertility, gynecological or obstetric problems, or contraceptive usage.Twins, Dizygotic: Two offspring from the same PREGNANCY. They are from two OVA, fertilized at about the same time by two SPERMATOZOA. Such twins are genetically distinct and can be of different sexes.WalesFathers: Male parents, human or animal.Siblings: Persons or animals having at least one parent in common. (American College Dictionary, 3d ed)Pregnancy Rate: The ratio of the number of conceptions (CONCEPTION) including LIVE BIRTH; STILLBIRTH; and fetal losses, to the mean number of females of reproductive age in a population during a set time period.Continental Population Groups: Groups of individuals whose putative ancestry is from native continental populations based on similarities in physical appearance.Placenta Previa: Abnormal placentation in which the PLACENTA implants in the lower segment of the UTERUS (the zone of dilation) and may cover part or all of the opening of the CERVIX. It is often associated with serious antepartum bleeding and PREMATURE LABOR.United StatesPregnancy Complications, Infectious: The co-occurrence of pregnancy and an INFECTION. The infection may precede or follow FERTILIZATION.Postpartum Period: In females, the period that is shortly after giving birth (PARTURITION).BrazilGenetic Testing: Detection of a MUTATION; GENOTYPE; KARYOTYPE; or specific ALLELES associated with genetic traits, heritable diseases, or predisposition to a disease, or that may lead to the disease in descendants. It includes prenatal genetic testing.alpha-Fetoproteins: The first alpha-globulins to appear in mammalian sera during FETAL DEVELOPMENT and the dominant serum proteins in early embryonic life.African Continental Ancestry Group: Individuals whose ancestral origins are in the continent of Africa.Confidence Intervals: A range of values for a variable of interest, e.g., a rate, constructed so that this range has a specified probability of including the true value of the variable.Body Mass Index: An indicator of body density as determined by the relationship of BODY WEIGHT to BODY HEIGHT. BMI=weight (kg)/height squared (m2). BMI correlates with body fat (ADIPOSE TISSUE). Their relationship varies with age and gender. For adults, BMI falls into these categories: below 18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0 and above (obese). (National Center for Health Statistics, Centers for Disease Control and Prevention)