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PubMed1995

Genesis of the retinal pigment epithelium in the macaque monkey.

The development of the retinal pigment epithelium (RPE) was studied in rhesus monkey (Macaca mulatta) fetuses, neonates, and juveniles exposed to a pulse of 3H-thymidine (3H-TdR) between embryonic day (E) 25 and postnatal day (P) 204 and examined at short and long intervals after the injection of the isotope. The RPE develops from the outer layer of the optic cup which by E45 consists of a multistratified epithelium. The outer layer appears immature near the retina's edge and gradually becomes monostratified and more mature centrally. Even at this early stage, all cells contain pigmented melanosomes, although peripherally the pigment is limited to the apical portion of the cells. Examination of autoradiograms from animals allowed to survive for several postnatal months shows that monkey RPE cell genesis begins just after E27, increasing to a peak frequency of 0.38 cells/mm at E43. Between E30 and E85 the density of radiolabelled cells varies within a restricted range of from 0.2 to 0.4 cells/mm (mean = 0.25 +/- 0.09). From the density of radiolabelled cells, and data on the overall density of RPE cells in the juvenile retina, we determined the labelling index. During the first half of gestation, between 0.38% and 0.99% (mean = 0.65 +/- 0.22) of RPE cells are generated during the short interval of isotope availability after pulse injection. Approximately 5% of RPE cells were generated by E33, and 50% by E71. After E85, RPE cytogenesis begins gradually to decrease, and 95% of the cells have been generated by the time of birth. Continued, very low density (0.01 cells/mm) cytogenesis in the RPE is seen at P17, and persists at least until seven months postnatally. RPE cell genesis begins near the fovea, and proceeds towards the periphery. Cell division largely ceases in both foveal and perifoveal regions by E56, at which time labelled cells first begin to appear peripheral to the equator. Besides the timing differences, RPE genesis in the central retina differs from that in the peripheral retina in that it proceeds at a higher rate, and lasts for a shorter time period. A prolonged postnatal period of low density RPE cell genesis persists in both central and peripheral retina. Comparison of the pattern of expansion of the area containing radiolabelled cells in the RPE and neuroretina demonstrates a remarkable spatial and temporal correspondence. Close analysis suggests that at any point on the retina, the last cells are generated in the neuroretina slightly before the last cells in the RPE.

Animals↗
PubMed1981

Factors impacting on the maternal role the first year of motherhood.

This study is exploring the nature of the relationships between key maternal and infant variables and maternal role attainment in a sample of 255 women who are experiencing motherhood for the first time. Data are being collected by instruments and semistructured interviews at 5 periods: early postpartum and at 1, 4, 8, and 12 months. Maternal variables under study include age, perception of the birth experience, early maternal-infant separation, social stress, support systems, personality traits, medical complications, child rearing attitudes, and self-concept; infant variables include temperament and illness. The objectives are to determine the form and strength of the relationships between the maternal and infant variables and maternal role attainment as measured at the 5 intervals for 3 groups of first-time mothers (age 13-19), 20-29, 30-39) and their significance in predicting the outcome of maternal role attainment upon a randomly selected subsample of the sample using multiple regression and cross validation techniques. Other factors that influence maternal role attainment will be identified and analyzed as they emerge from interviews. The currently high refusal rate to participate (48%) suggests that the final sample will not be representative. Refusals may reflect unique stressors or personality characteristics which also correlate with increased difficulties with the maternal role. A common concern and difficulty for mothers at 1 month are the unexpected demands of motherhood, although 1 cultural group has not viewed these as bothersome. Mothers' expectations for themselves and their infants range from realistic to unrealistic.

Adolescent↗
PubMedDate not supplied

Effects of exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB 126) throughout gestation and lactation on behavior (concurrent random interval-random interval and progressive ratio performance) in rats.

There is evidence that polychlorinated biphenyl (PCB) congeners have differential effects on endpoints of neurotoxicity depending on their chemical structure: specifically, that ortho-substituted congeners are neurotoxic while coplanar (dioxin-like) congeners are relatively inactive in producing neurotoxic effects. This study extends research on the effects of developmental exposure to the coplanar congener 3,3',4,4',5-pentachlorobiphenyl (PCB 126) in Long-Evans rats. Dams were dosed with 0, 0.25, or 1 microg/kg/day Monday to Friday beginning 5 weeks before and continuing through gestation and lactation. The first 2-week breeding period produced 10, 7, and 13 litters in the three dose groups, respectively, used in behavioral assessment. Breeding females from the control and low-dose group that did not conceive were rebred after 76 days of dosing, producing six and six litters used in behavioral testing. This regimen of PCB exposure produced reduced weight gain between birth and weaning in cohort 1, and decreased thyroxine levels and changes in hematology and serum biochemistry parameters in both cohorts. One female and male from each litter were tested under a series of three concurrent random interval-random interval (RI-RI) schedules of reinforcement beginning at about 400 days of age, followed immediately by assessment under a progressive ratio (PR) schedule. The concurrent RI-RI allows assessment of performance during steady state and during behavior in transition (learning). The PR schedule provides the opportunity to assess the strength of the reinforcing event independent of response rate. During the first RI-RI schedule, the high-dose group apportioned responses less accurately than controls with respect to the scheduled relative reinforcement density on the two levers. There was also some evidence for differences in performance between treated and control groups on the third RI-RI schedule of reinforcement. There was no evidence for differences in the relative strength of the reinforcing event as assessed by PR performance. These same rats failed to exhibit PCB-induced impairment on a spatial delayed alternation task or under multiple fixed interval-fixed ratio or DRL schedules of reinforcement, performed prior to the current experiments. These data extend previous findings concerning the pattern of behavioral effects as a consequence of gestational and lactational exposure to a dioxin-like PCB congener.

Animals↗
PubMed1993

Biological determinants of pregnancy weight gain in a Filipino population.

Patterns of pregnancy weight gain and predictors of first trimester and total weight gain were investigated in a sample of 1367 women from Cebu, Philippines, with pregnancy intervals of < 2 y. The mean total weight gain based on actual measurements of prepregnant weight was 8.4 kg. Controlling for gestational week when weight was measured, multivariate-regression models predicted higher first trimester weight gain with higher parity, lower prepregnant body mass index (BMI), and longer nonpregnant intervals. Higher total weight gain was associated with longer nonpregnant intervals, lower prepregnant BMI, taller maternal stature, and relatively high dietary energy intakes. Lactation into the third trimester of pregnancy and maternal age over 35 y had significant negative effects on total weight gain. Given the importance of maternal weight gain in predicting birth outcome, this study provides information on modifiable risk factors that should be considered when developing maternal-infant health policy and programs.

Adolescent↗
PubMed2000

Early pregnancy predictors of preterm birth: the role of a prolonged menstruation-conception interval.

OBJECTIVE: To study early pregnancy characteristics as possible risk factors associated with preterm birth. DESIGN: Retrospective analysis of prospectively collected maternity data. POPULATION: 21,069 singleton deliveries with record of a specified last menstrual period and a midtrimester dating scan. SETTING: Catchment area of tertiary centre serving a general maternity population. METHODS: Univariate and multivariate analysis. Variables included: maternal age; height; weight at first visit; parity; ethnic group; cigarette smoking and alcohol consumption recorded in early pregnancy; history of abortion; history of preterm birth; and discrepancy between menstrual dates and ultrasound dates. MAIN OUTCOME MEASURES: Adjusted odds ratios for factors associated with preterm birth, stratified according to parity (nulliparae vs multiparae) and gestational age (early preterm, 24-33 weeks; late preterm, 34-36 weeks; all preterm, < 37 weeks). Population attributable risk (aetiologic fraction) of the significant variables for preterm birth. RESULTS: The overall preterm (< 37 weeks) delivery rate according to scan dates was 7 x 0%. Preterm birth was associated with young (< 20 years), short (< or = 155 cm) and underweight (< or = 52 kg) mothers, non-Europeans, cigarette smokers, previous abortion or previous preterm delivery, and a prolonged menstruation-conception interval. Preterm births which followed the spontaneous onset of labour (72%) had results which were similar to the overall group, while there were too few iatrogenic preterm deliveries for separate analysis. Logistic regression showed that associations varied in different parity and gestational age groups. For nulliparae, smoking was not associated with preterm birth, but it was strongly associated with multiparous women (adjusted OR 1 x 8, 95% CI 1 x 6-2 x 1). A past history of premature delivery had the highest risk for birth before 34 weeks in the index pregnancy (adjusted OR 5 x 1, 95% CI 3 x 4-7 x 6). A discrepancy between menstrual and scan dates of greater than +7 days, suggestive of a prolonged interval between last menstruation and conception, was present in 23 x 3% of all pregnancies, and was associated with an increased risk of preterm delivery in all gestational age categories for nulliparae (adjusted OR 1 x 5, 95% CI 1 x 3-1 x 8) and multiparae (adjusted OR 1 x 9, 95% CI 1 x 6-2 x 2). Because of its high prevalence, this variable constituted a relatively high population-attributable risk for premature birth for both nulliparae (10 x 7%) and multiparae (16 x 6%). CONCLUSIONS: A discrepancy of more than +7 days between menstrual and scan dates, indicating a prolonged interval between last menstruation and conception, is a significant predictor of preterm birth. This effect is independent of other factors such as maternal age, height, weight and smoking which are also associated with prematurity. In a maternity population with ultrasound scan dates and recorded last menstrual period, this variable can be easily calculated and used as a marker for increased surveillance.

Analysis of Variance↗
PubMed1987

Formation of primary and secondary myotubes in rat lumbrical muscles.

Numbers of myoblasts, primary myotubes and secondary myotubes in developing rat embryo hindlimb IVth lumbrical muscles were counted at daily intervals up until the time of birth, using electron microscopy. Motoneurone death at the spinal cord level supplying the lumbricals was assessed by counting axons in the 4th lumbar ventral root. Death of the motoneurones that supply the intrinsic muscles of the hindfoot was monitored by comparing the timecourse of development of total muscle choline acetyltransferase activity in control embryos with that in embryos where motoneurone death was inhibited by chronic paralysis with TTX, and by counting axons in the mixed nerve trunks at the level of the ankle at daily intervals. Condensations of undifferentiated cells marking the site of formation of the muscle were seen on embryonic day 15 (E15). Primary myotubes began to appear on E16 and reached a stable number (102 +/- 4) by E17. Secondary myotubes first appeared two days later, on E19, and numbered 280 at the time of birth (E22). The adult total of about 1000 muscle fibres, derived from both primary and secondary myotubes, was reached at postnatal day 7 (PN7) so considerable generation of secondary myotubes occurred after birth. There was a linear correlation between the number of undifferentiated mononucleate cells in a muscle and the rate of formation of secondary myotubes. The major period of motoneurone death in lumbar spinal cord was during E16-E17, when axon numbers in the L4 ventral root fell from 12,000 to 4000, but a discontinuity in the curve of muscle ChAT activity versus time indicated that death in the lumbrical motor pool occurred during E17-E19, after all primary myotubes had formed and before generation of secondary myotubes began. We suggest that motoneurone death, by regulating the final size of the motoneurone pool, regulates the ratio of secondary to primary myotube numbers in a muscle.

Animals↗
PubMed1975

Nosocomial and maternally acquired herpesvirus hominis infections. A report of four fatal cases in neonates.

Four fatal cases of neonatal herpes simplex infection occurred during a two-month period in the perinatal intensive care unit of a hospital. Virus isolation or serologic studies, or both, implicated herpesvirus hominis type 2 in all four cases. Three of the infants developed symptoms in the first week of life and were probably infected in utero or at delivery. The fourth infant did not develop signs of illness until age 6 weeks, an interval much longer than that expected with disease acquired at birth. An epidemiologic investigation indicated that the most likely source of this fourth infant's herpes infection was by indirect contact with one of the other three infected neonates. Nosocomial spread of herpes simplex virus within a hospital nursery, although uncommon, may pose an added risk to the newborn infant if nursery techniques among infants are compromised.

Adolescent↗
PubMed2003

Plasma sex steroid hormones and breast cancer risk in Chinese women.

Estrogens regulate the growth and differentiation of mammary cells and play an important role in the development of breast cancer. High circulating levels of estrogens are associated with increased risk of breast cancer in Caucasian women. Because Asian women have low estrogens in the circulation compared with their Caucasian counterparts, the effect of estrogens on breast cancer risk in populations with low circulating estrogens remains to be elucidated. We conducted a population-based case-control study in China to evaluate the association of sex steroid hormones with breast cancer risk in Chinese women. Our study included 300 incident cases with primary breast cancer and 300 age- and menopausal status-matched healthy controls randomly selected from the general population in Shanghai. Fasting blood samples were collected from cases prior to any treatment and from their matched controls. Commercial immunoassays were used to measure plasma concentrations of estradiol, estrone, estrone sulfate, testosterone, progesterone, dehydroepiandrosteindian sulfate (DHEA-S) and steroid hormone-binding globulin (SHBG). Conditional logistic regression analysis was performed to examine the association between steroid hormones and breast cancer risk. The results showed that breast cancer risk was elevated with increasing levels of estrone and testosterone (p for trend < 0.05) but not with DHEA-S, estradiol, estrone sulfate, progesterone or SHBG. The estimated relative risks between upper and lower tertiles were 2.07 (95% confidence interval [CI] 0.97-4.41) for estrone in postmenopausal women, 2.01 (95% CI 0.96-4.21) for testosterone in premenopausal women, and 2.40 (95% CI 1.11-5.21) for testosterone in postmenopausal women, after adjusting for age at first live birth, waist-to-hip ratio, total calorie intake, a history of fibroadenoma, a family history of breast cancer and SHBG. These results, in general, are consistent with the findings in Caucasian women and indicate that high sex steroid hormones in the circulation, both androgen and estrogen, are associated with increased risk of breast cancer even in populations with relatively low sex hormones.

Adult↗
PubMed1998

Perinatal mortality in breech presentation sibships.

OBJECTIVE: To compare perinatal mortality in breech presentation delivered vaginally and by cesarean in individual births and in sibships. METHODS: A national, population registry-based study, 1967-1994, was conducted, with maternal record linkage of sibships, comprising the first to the third birth of a mother. The main outcome was perinatal mortality. Odds ratios of perinatal mortality were calculated and adjusted by logistic regression analysis. RESULTS: The overall relative perinatal mortality was 4.3 (95% confidence interval [CI] 4.1, 4.5) in breech compared with nonbreech presentation and 5.4 (95% CI 4.7, 6.2) in vaginal compared with cesarean delivery. The relative perinatal mortality in breech compared with nonbreech presentation was lowest in birth order one compared with birth orders two and three. In breech vaginal delivery compared with cesarean delivery, the opposite effect of birth order was found. The highest perinatal mortality was found in a current breech presentation of a sibship with no previous breech births. In birth subsequent to breech births, perinatal mortality was more or less independent of current presentation, without respect to delivery method. The increased perinatal mortality in breech presentation is explained partly by its association with other risk factors for perinatal death. CONCLUSION: Women with recurring breech presentation represent a lower risk of adverse perinatal outcome. This might be explained by a biologic mechanism or by increased quality of antenatal care. An increased mortality in subsequent nonbreech siblings after a breech presentation was surprising.

Breech Presentation↗
PubMed2005

Breastfeeding prevalence and practices among Singaporean Chinese, Malay and Indian mothers.

The National Breastfeeding Survey 2001 was the first comprehensive study on breastfeeding conducted on a national level in Singapore. It aimed to establish the prevalence of breastfeeding among Chinese, Malay and Indian mothers and to identify factors influencing breastfeeding. A total of 2098 mothers were interviewed in this two-phase study, with the first interview conducted 2 months after delivery and the second interview 6 months after birth among mothers who were still breastfeeding at 2 months. Frequency distributions of breastfeeding prevalence and types of breastfeeding practices at different time intervals (from birth to 6 months) were produced. Multivariate logistic regression was carried out to construct a model with predictive information on factors which influence continued breastfeeding till 2 months and 6 months after delivery respectively. The study found that about 94.5% of the mothers attempted breastfeeding. At 1 month, 71.6% were still breastfeeding, 49.6% continued to do so at 2 months, and 29.8% persisted till 4 months. By 6 months, the breastfeeding prevalence rate fell to 21.1%. The results of this study show higher breastfeeding prevalence rates compared to past studies in Singapore. Despite this, exclusive breastfeeding is still not a common practice. Various factors were found to be significant in influencing mothers' decision to breastfeed. Factors such as ethnicity, age, educational attainment, religion and baby's sex are non-modifiable in the short term or at an individual level. However, factors such as awareness of breastfeeding benefits, advice from health professionals and previous breastfeeding experience are potentially modifiable. Efforts aimed at promoting breastfeeding in Singapore need to take these modifiable factors into consideration so as to better tailor health promotion efforts on breastfeeding to women.

Adult↗
PubMed1994

Validation of the Gail et al. model for predicting individual breast cancer risk.

BACKGROUND: The Gail et al. model is considered the best available means for estimating an individual woman's risk of developing breast cancer. Such estimates are useful in decision making on the part of women, in designing prevention trials, and in targeting screening and prevention efforts. PURPOSE: Our purpose was to evaluate the ability of the model to accurately predict individual breast cancer risk, using a large population independent of the one from which the model was derived. METHODS: We compared the number of cancer cases predicted by the model to the actual number of cases observed in the Nurses' Health Study. The study population was 115,172 women who did not have breast cancer at the beginning of the study. Questionnaires were sent to participants every 2 years, seeking data on risk factors and diagnoses of breast cancer. Follow-up compliance was 95% over the 12-year study period. RESULTS: The model over-predicted absolute breast cancer risk by 33% (95% confidence interval [CI] = 28%-39%), with the overprediction more than twofold among premenopausal women (95% CI = 1.9-2.2), among women with extensive family history of breast cancer (95% CI = 1.1-3.9), and among women with age at first birth younger than 20 years (95% CI = 1.3-4.7). The correlation coefficient between observed and predicted risk was 0.67, indicating that the model is less than satisfactory for ranking individual levels of breast cancer risk. Overprediction occurred at all deciles of predicted risk. CONCLUSIONS: The model's performance is unsatisfactory for estimating breast cancer risk for individual women aged 25-61 years who do not participate in annual screening. Lower mammography screening rates in the Nurses' Health Study may account for some, but not all, of the discrepancy between observed and predicted cases. IMPLICATIONS: A recent modification of the model by the tamoxifen trial investigators is likely to have provided accurate power calculations. This modified form of the model should be useful for planning other large, population-based studies.

Adult↗
PubMed1997

Unintended childbearing, maternal beliefs, and delay of prenatal care.

BACKGROUND: Delay of prenatal care is an important risk for poor birth outcome, yet its association with maternal knowledge and beliefs remains insufficiently studied. This research examined the relationship of unintended childbearing and beliefs about the importance of prenatal care with initiation after the first trimester, adjusting for key sociodemographic determinants. METHODS: One hundred fifty-four Texas hospitals accounting for 80 percent of state births were asked to collect surveys from all women delivering infants during a one-week interval in 1986. Seventy-four percent of hospitals and 70 percent of women participated (n = 2032). No differences occurred between the sample and the population on rates of delayed care and low birthweight or maternal demographics. RESULTS: Since delayed prenatal care is more frequent among low-income women, analyses were limited to those below the 200 percent poverty level. After adjustment for maternal age, marital status, education, parity, race, and health insurance status employing logistic regression, unintended births were 1.6 times more likely to involve delayed care. Mothers who believed prenatal care was unimportant were 2.1 times more likely to delay care. These coefficients exceeded or about equaled those for the covariates. CONCLUSIONS: Preconception education about the value of prenatal care and family planning programs to prevent unintended pregnancies should be conducted together with efforts to overcome financial and structural barriers if progress toward national prenatal care objectives is to be achieved.

Adult↗
PubMed1996

Maternal HIV and drug use: effect on health and social morbidity.

A retrospective analysis of routine child health surveillance information was performed on health visitor records of 459 children, to examine the independent effects of maternal HIV infection and drug use during pregnancy on morbidity in the first 3 years of life. No significant differences were observed in the developmental progress of children born to HIV infected or drug using women when compared to community controls. The pattern of medical consultations in the first 18 months of life was significantly different, maternal drug use exerting a negative influence on outpatient visits (odds ratio 0.6, 95% confidence interval 0.4 to 1.0). At 6 weeks, the majority of children lived with their birth parent(s), and no differences were observed between the groups. By 10 months of age, only 81% of children born to HIV infected drug using women lived with their parent(s). While maternal drug use and HIV did not have adverse effects on child health and development, these findings highlight the social implications for children affected by the heterosexual spread of HIV.

Adult↗
PubMed1989

Dietary folate as a risk factor for neural-tube defects: evidence from a case-control study in Western Australia.

A population-based case-control study was conducted to test the hypothesis that the risk of the occurrence of neural-tube defects in infants with no other birth defects (isolated neural-tube defects) is associated inversely with the maternal dietary intake of free and/or total folate in early pregnancy. Information was collected from the mothers of 77 case subjects with isolated neural-tube defects who were born in Western Australia from 1982 to 1984, from the mothers of 77 control subjects with birth defects other than neural-tube defects (control group 1) and from the mothers of 154 control subjects with no birth defects (control group 2). The case and control subjects were matched individually by the date of the mother's last menstrual period. Odds ratios were adjusted for a number of potentially-confounding variables, such as the country of birth of the parents, paternal social class, previous pregnancy outcome, interval between index and previous pregnancy and pregnancy order. Crude and adjusted odds ratios showed a protective effect of an increasing intake of free folate in the first six weeks of pregnancy. Adjusted odds ratios, with reference to the lowest quartile of intake, (and their 95% confidence intervals) were 0.72 (0.25-2.08), 0.37 (0.11-1.23) and 0.31 (0.10-0.97) for quartiles 2-4 when control group 1 was used, and 0.44 (0.17-1.13), 0.34 (0.13-0.90) and 0.16 (0.06-0.49) when control group 2 was used. Similar, but weaker, trends were seen when total folate intake was the exposure variable. These findings support the hypothesis that the dietary intake of folate in early pregnancy protects against the occurrence of isolated neural-tube defects in infants. Measures of postpartum dietary folate and of postpartum serum and red-cell folate levels showed no association with the occurrence of neural-tube defects in infants.

Diet↗
PubMed1996

Lactose metabolism and time to pregnancy.

OBJECTIVE: To investigate whether, in the absence of galactosemia, relatively high intestinal lactase activity or low activity of an enzyme involved in galactose catabolism reduces fertility, as it does in the presence of galactosemia. DESIGN: Retrospective cohort study. SETTING: Healthy women selected from the community. PATIENTS: Fifty-three married women. INTERVENTION: Urinary galactose after an oral lactose challenge (a measure of intestinal lactase activity), erythrocyte galactose-1-phosphate uridyltransferase (transferase) activity, and transferase polymorphisms by isoelectric focusing. MAIN OUTCOME MEASURE: Pregnancy rate (number of pregnancies divided by number of months at risk) in the 12 months after stopping use of birth control to become pregnant. RESULTS: Relatively high urinary galactose was not related to a decreased rate of pregnancy during the first 12 months (> or = 24.6 compared with < or = 14.3 mg: relative risk [RR] = 1.9; 95% confidence interval [CI] = 0.86 to 4.0). Relatively high transferase activity was not related to an increased rate of pregnancy (> or = 19.5 compared with < or = 17.2 mumol/h per g hemoglobin: RR = 1.1; 95% CI = 0.56 to 2.4). Low-activity transferase polymorphisms were not related to a decreased rate (RR = 1.2; 95% CI = 0.58 to 2.5). CONCLUSION: Our study does not support the hypothesis that the biologic variation in galactose metabolism that exists in the general population influences infertility.

Adolescent↗
PubMed2000

Identification of quantitative trait loci affecting birth characters and accumulation of backfat and weight in a Meishan-White Composite resource population.

A search for genomic regions affecting birth characters and accretion of weight and backfat was conducted in a Meishan-White Composite reciprocal backcross resource population. Birth traits analyzed (n = 750) were vigor score, number of nipples, and birth weight. Subsequent measures on gilts and barrows (n = 706) analyzed were weaning weight, 8-wk weight, ADG from 8 to 18 wk of age, ADG from 18 to 26 wk of age, 26-wk weight, and backfat over the first rib, last rib, and last lumbar vertebrae at 14 and 26 (n = 599) wk of age. Feed intake and growth of 92 individually penned barrows were also analyzed. A genomic scan was conducted with microsatellite markers spaced at approximately 20-cM intervals, a least squares regression interval analysis was implemented, and significance values were converted to genomewide levels. No associations were detected for traits measured at birth except for number of nipples, where one significant and two suggestive regions were identified on chromosomes (SSC) 10, 1, and 3, respectively. Early growth was affected by a region on SSC 1 as evidenced by associations with weights collected at weaning and 8 wk of age and ADG from 8 to 18 wk of age. Other regions detected for early growth rate were on SSC 2, 12, and X. Chromosomal regions on SSC 6 and 7 affected ADG from 18 to 26 wk of age. All measures of backfat were affected by regions on SSC 1 and X, whereas SSC 7 consistently affected backfat measures recorded at 26 wk of age. Suggestive evidence for QTL affecting backfat at 14 wk of age was also detected on SSC 2, 6, 8, and 9. These results have improved our knowledge about the genetics of growth rate and fat accretion at the molecular level in swine.

Adipose Tissue↗
PubMed2001

Rates of preterm delivery among Black women and White women in the United States over two decades: an age-period-cohort analysis.

The authors assessed the influence of age, period, and cohort effects on rates of preterm delivery in the United States. Rates of preterm delivery for singleton births (<37 weeks) in seven age groups (15-19, 20-24,., 45-49 years), five periods (1975, 1980, 1985, 1990, 1995), and 11 maternal birth cohorts (1926-1930, 1931-1935,., 1976-1980) were examined. Over the 20-year study interval, preterm delivery increased by 3.6% among Blacks (from 15.5% in 1975 to 16.0% in 1995) and by 22.3% among Whites (from 6.9% to 8.4%). Among Black primigravid women, rates of preterm delivery increased from 1975 to 1990 and began to decline thereafter; among Whites, the rates increased between 1975 and 1995. In Blacks, women aged 25-29 years had the lowest rates for the first and second births, and women aged 30-34 years had the lowest rate for subsequent births. In Whites, the age groups with the lowest preterm delivery rates were 20-24 years for first births and 25-29 years for subsequent births. Cohort-specific rates of preterm delivery remained fairly constant across age strata and periods for Whites, but a small trend was apparent for Blacks aged 30-44 years. The consistency of the observed age effects across periods and cohorts suggests that the age effect is partly due to biologic factors. The presence of period effects might be linked to the increased survival of premature infants or to increased viability among births occurring at lower lengths of gestation.

Adolescent↗
PubMed1992

Characteristics of second labor occurring 10 or more years after the first.

Labor characteristics in 89 women undergoing a second vaginal delivery 10-18 years after the first were compared retrospectively with those of 136 women with an interval of 1-4 years between their first and second vaginal deliveries and with those of 128 nulliparous women. The pelvic findings on admission, average length of stages 1 and 2 of labor, average cervical dilation per hour and rates of surgical intervention in relation to arrest disorders were similar in the two multiparous groups and significantly different from these parameters in the nulliparous group. Women with long intervals between their first and second vaginal deliveries should be managed in the same way as are other multiparas and not like nulliparas with respect to such issues as indications for oxytocin treatment, surgical intervention and use of conduction anesthesia.

Adult↗