Reexamination of interpregnancy intervals and subsequent birth outcomes: Evidence from U.S. linked birth/infant death records

Abstract

This study examines the net effects of the interpregnancy interval (time period from one birth to the next pregnancy) on the risks of preterm birth, intrauterine growth retardation, and infant mortality, for blacks and whites separately, using data from 1991 U.S. Linked Birth‐Infant Death files. Results show that short (less than 7 months) and long (61+ months) intervals between pregnancies raise the risk of preterm birth and intrauterine growth retardation for both race groups, though the increase in risk is generally less than 30 per cent. Short intervals also raise (slightly) the risk of infant mortality after controlling for birthweight and gestational age.     

Birth order,gestational age,and risk of delivery related perinatal death in twins: retrospective cohort study

ObjectiveTo determine whether twins born second are at increased risk of perinatal death because of complications during labour and delivery.DesignRetrospective cohort study.SettingScotland, 1992 and 1997.ParticipantsAll twin births at or after 24 weeks'' gestation, excluding twin pairs in which either twin died before labour or delivery or died during or after labour and delivery because of congenital abnormality, non-immune hydrops, or twin to twin transfusion syndrome.ResultsOverall, delivery related perinatal deaths were recorded for 23 first twins only and 23 second twins only of 1438 twin pairs born before 36 weeks (preterm) by means other than planned caesarean section (P>0.99). No deaths of first twins and nine deaths of second twins (P=0.004) were recorded among the 2436 twin pairs born at or after 36 weeks (term). Discordance between first and second twins differed significantly in preterm and term births (P=0.007). Seven of nine deaths of second twins at term were due to anoxia during the birth (2.9 (95% confidence interval 1.2 to 5.9) per 1000); five of these deaths were associated with mechanical problems with the second delivery following vaginal delivery of the first twin. No deaths were recorded among 454 second twins delivered at term by planned caesarean section.ConclusionsSecond twins born at term are at higher risk than first twins of death due to complications of delivery. Previous studies may not have shown an increased risk because of inadequate categorisation of deaths, lack of statistical power, inappropriate analyses, and pooling of data about preterm births and term births.

What is already known on this topic

It is difficult to assess the wellbeing of second twins during labourDeliveries of second twins are at increased risk of mechanical problems, such as cord prolapse and malpresentation, after vaginal delivery of first twinsIncreased risks of perinatal death in second twins have not been shown, but the methods of these studies were flawed

What this study adds

Second twins delivered at term are at increased risk of delivery related perinatal deathsIntrapartum anoxia caused 75% of these deaths in second twins, and most of these resulted from mechanical problems after vaginal delivery of first twinsPlanned caesarean section of twins at term may prevent perinatal deaths     

Heredity counseling

Abstract

An ecological analysis of infant mortality rates is conducted using data on Texas counties for the years 1968–72. It is found that when counties along the Texas‐Mexico border (which have unreasonably low infant death rates and which are economically less advantaged than the remainder of the counties) are excluded from the analysis, the associations between socioeconomic status variables and infant mortality rates improve considerably. A significant negative correlation between neonatal mortality and per cent Spanish surname is retained and does not disappear when the effects of other relevant variables (per cent Negro, per cent urban, and per cent below poverty) are controlled using partial correlation and regression analysis. Possible explanations for this unexpected finding are suggested, and implications for further research are discussed.     

Statistical Analyses of Twins Birth Data from a Nigerian Sample

In this paper, both the linear logistic model and its analogous linear model (weighted least squares) are fitted to twin birth data from a Nigerian sample. The logits of the observed perinatal mortality rates are fitted against the birthweight of breech infants for both first born and second born twins. Results show that a quadratic response model fits the data very well, and that the WLS procedure gives a better fit. The results further show that breech births necessarily result in 7.7% and 11.2% mortality rates respectively for first born and second born twins. The results of a log-linear model analysis on the 2×2×4 contingency table formed by the factors, ‘mode of birth’, and twins with the response variable ‘Apgar Scores’-an index of morbidity-also show that both factors play significant roles in explaining the variation of the response variable. It was found that the most important factor effecting the ability of a twin infant to survive as measured by the Apgar scores is the variable ‘mode of birth’ (vertex or breech). In other words, a vertex first twin infant has the best survival chance.     

Selection intensities in mothers of twins and in mothers of singletons

Abstract

Opportunity for selection was assessed in a group of mothers with twins and was compared with estimates obtained in mothers who gave birth to singletons only from the same population. Both groups were matched on a number of confounding variables in the framework of a case/control methodology. Two time periods involving demographic changes were studied separately. After appropriate adjustment for the increased family size of mothers of twins, results show that selection intensities are greater in twin‐bearing mothers than in controls. The fertility component of the selection index is lower than that of mortality if childless women are taken into account. However, the index of opportunity for selection is rather low by current standards but, given the methodology used, should reflect genetic rather than environmental selection. Notwithstanding, it would be difficult to explain the recent change in the twinning rates in the population by the actual level of selection indices.     

Contraceptive practices and fertility among Southeast Asian,black, and white mothers attending a maternal infant care program

Abstract

The purpose of this analysis was to determine if there were differences in selected fertility characteristics including parity, pregnancy spacing, age at first pregnancy, age of menarche, breastfeeding postpartum, and contraceptive practices among white, black, Hmong, and other Southeast Asian mothers attending a maternal infant care program in Minneapolis, Minnesota, during 1980–82.

White and black mothers were younger than the Hmong and other Asian mothers. The lowest mean age of first pregnancy was among blacks. Ages of first pregnancy were similar for whites, Hmong, and other Asians, although the mean age of menarche was approximately two years later for Hmong and other Southeast Asian mothers compared to the white and black mothers.

Based on self reports at the first postpartum visit one month after delivery, 39 per cent of the whites and 25 per cent of the blacks were breastfeeding. In comparison 8.7 per cent of the Hmong and 17 per cent of the other southeast Asian mothers were breastfeeding.

Maternal age and age at first pregnancy were significant predictors of parity for whites, blacks, Hmong, and the other Southeast Asians. Ever‐use of contraception was a significant predictor of parity only for Hmong.

The highest proportion of ever‐users of contraception was among the white mothers (80 per cent) followed by the blacks (69.3 per cent) and other Asian mothers (34.8 per cent). Hmong mothers had the lowest proportion having used contraception (17.1 per cent).     

The Danish Twin Registry: 127 birth cohorts of twins.

The Danish Twin Registry is the oldest national twin register in the world, initiated in 1954 by ascertainment of twins born from 1870 to 1910. During a number of studies birth cohorts have been added to the register, and by the recent addition of birth cohorts from 1931 to 1952 the Registry now comprizes 127 birth cohorts of twins from 1870 to 1996, with a total of more than 65,000 twin pairs included. In all cohorts the ascertainment has been population-based and independent of the traits studied, although different procedures of ascertainment have been employed. In the oldest cohorts only twin pairs with both twins surviving to age 6 have been included while from 1931 all ascertained twins are included. The completeness of the ascertainment after adjustment for infant mortality is high, with approximately 90% ascertained up to 1968, and complete ascertainment of all liveborn twin pairs since 1968. The Danish Twin Registry is used as a source for large studies on genetic influence on aging and age-related health problems, normal variation in clinical parameters associated with the metabolic syndrome and cardiovascular diseases, and clinical studies of specific diseases. The combination of survey data with data obtained by linkage to national health related registers enables follow-up studies both of the general twin population and of twins from clinical studies.     

The influence of birth timing upon infant growth and survival in Captive Rhesus Macaques (Macaca mulatto)

Weights, growth rates, and mortality data of 815 captive-born Macaca mulattainfants were studied to determine if date of birth influences infant growth and survival. The six groups studied displayed a unimodal spring-summer birth season that has become systematically more restricted since 1977. Males exhibited higher rates of stillbirth and neonatal death and were more frequently born outside the normal birth season, when infant mortality was more common. Within the normal birth season, infant weight increased linearly with birth date, and infant growth rate declined linearly with birth date. Female infants with weights and growth rates near the developmental norm, especially those born in the middle of the birth season, have the greatest probability of survival. Males are more likely to survive if their weights and growth rates exceed the developmental norm, and thus male infants might be initially more costly to produce than female infants. These results are inconsistent with the hypothesis that offspring of high-ranking males, which conceived predominantly in the first third of the breeding season, enjoy a selective advantage.     

Evaluating 2 year outcome in twins < or = 30 weeks gestation at birth: a regional perinatal unit's experience.

With improved technology in assisted reproductive medicine, there has been an absolute increase in the numbers of twin pregnancies with an associated increase in perinatal mortality and morbidity. This increase in perinatal mortality and morbidity is largely due to a higher incidence of delivering preterm as compared to singletons. Twin pregnancies have their unique complications that include abnormal placental communication and discordant growth which are associated with perinatal mortality and morbidity. The objectives of this study were two-fold: i) to determine if the morbidity/mortality outcome at 18-24 months corrected age seen in a cohort of twins born between 24-30 weeks gestation was significantly different as compared to singleton preterm infants of the same gestation; and ii) to determine and evaluate any differences between monochorionic (MC) and dichorionic (DC) twins. Twins 24-30 weeks gestation at birth born between 01/01/97-30/06/99 were identified and prospectively followed to 18-24 months corrected age (c.a.). They were matched with a singleton infant of the same gender and within 1 week of the same gestation. Obstetrical, neonatal and neurodevelopmental data were gathered and analyzed. The primary outcome was death or the presence of a severe neurodevelopmental deficit at 18-24 months corrected age. Of the 56 sets of twins identified, 52 sets were followed prospectively with 101 infants available for matching. In this cohort, twin pregnancies had a lower incidence of pregnancy-induced hypertension and premature rupture of membranes than singletons (p < 0.05). The two groups were comparable in neonatal characteristics. The incidence of death or severe disability was 29.7% in twins vs. 22.8% in singletons (p = 0.337, Fisher's exact test). The major area of defect was in the cognitive category for both groups, 9.9% vs. 7.9% respectively. MC twins made up 35.6%; DC twins 64.4%. Twin to twin transfusion syndrome (TTTS) occurred in 6.9%. Discordant growth occurred more frequently in MC pregnancies (p = 0.016). MC twins tended to be more premature, lower in birth weight, and experience neonatal morbidity in the form of patent ductus arteriosus and sepsis (p < 0.05) as compared to DC twins. However, the primary outcome of death or severe neurodevelopmental deficit at 18-24 months c.a. was not significantly different between the two groups, 38.9% (MC) vs. 24.6% (DC), (p = 0.173, Fisher's exact test). Neurodevelopmental morbidity or mortality in twins with TTTS was 42%. Mortality and severe neurodevelopmental morbidity were not signif cantly higher in twins as compared to singletons in this cohort. However, the trend is slightly higher in twins, which may have clinical significance. Though not statistically significant, the incidence of 38.9% in adverse outcome wth MC twins may be clinically significant. With the number of twins steadily increasing, further monitor ng is required to determine future directions in intervention and research. Early recognition of monochorionicity remains essential to optimize care and neurodevelopment for these infants.     

Extrinsic Mortality Effects on Reproductive Strategies in a Caribbean Community

Extrinsic mortality is a key influence on organisms’ life history strategies, especially on age at maturity. This historical longitudinal study of 125 women in rural Domenica examines effects of extrinsic mortality on human age at maturity and pace of reproduction. Extrinsic mortality is indicated by local population infant mortality rates during infancy and at maturity between the years 1925 and 2000. Extrinsic mortality shows effects on age at first birth and pace of reproduction among these women. Parish death records show huge historical variation in age-specific mortality rates. The infant mortality rate (IMR) in the early 1920s was low, increased dramatically beginning in 1929, and reached a maximum in the 1950s, at which point IMR declined steadily to its present low rate. The mortality rate early in life showed a quadratic association with age at first birth. Women who experienced conditions of low IMR early in life reproduced relatively late in life. Those born into moderately high levels of infant mortality tended to reproduce earlier than those born at low levels. At very high infant mortality levels early in life, women went on to delay reproduction until relatively late, possibly as a result of somatic depletion and energetic stress associated with the conditions that lead to high IMR. Population mortality rates at age of maturity also showed a quadratic association with age at first birth. The pace of reproduction, estimated as number of surviving offspring controlled for maternal age, showed a similar quadratic effect. There were complex interactions between population mortality rates in infancy and at maturity. When extrinsic mortality was high during infancy, extrinsic mortality later in life had little effect on timing of first birth. When extrinsic mortality was low to moderate in infancy, extrinsic mortality later in life had significant effects on adult reproduction. I speculate that these effects are mediated through development of personality facets associated with reproduction.     

Blood group and behavioral differences among dizygotic twins: A failure to replicate

Abstract

The relationship between the age of mother and pregnancy outcome is examined using the matched birth‐infant death data for Arkansas. Indicators of pregnancy outcome are examined in relation to measures of SES and access to health care. The hypothesis that the elevated rate of newborn mortality and morbidity among infants delivered by adolescents as a consequence of biologic immaturity is examined. The analysis suggests that the higher levels of obstetric risk observed among teenage mothers is an artifact of lower SES and inferior access to health care and not biological immaturity as previously assumed.     

Etiology of individual differences in birth weight of twins as a function of maternal smoking during pregnancy.

Birth weight is in large extent influenced by gestational age. In addition genetic and environmental factors determine intrauterine growth and birth weight. The contributions of these factors may be influenced by maternal smoking during pregnancy. We examined birth weight and maternal smoking in a sample of 2930 twin pairs from the Netherlands Twin Register using structural equation modelling. Gestational age accounted for 27-44% of the variance in birth weight. A lower variability of birth weight and a lower association of birth weight with gestational age was found in twins whose mothers smoked during pregnancy. The variance not associated with gestational age was independent of maternal smoking during pregnancy. A systematic smaller part of the variability in birth weight was associated with variability in gestational age in second born twins compared to first born twins. The heritability of interindividual differences in birth weight was modest (10% for twins with non-smoking mothers and 11% for twins with smoking mothers). Common environmental influences other than gestational age accounted for a slightly larger part of the variance not associated with gestational age (17-20%).     

Factors influencing genetic counseling attendance rate: A geographically based study

Abstract

A study of factors influencing genetic counseling attendance rate has been conducted in the Bouches‐du‐Rhône area, in the south of France. In this area, a birth defects monitoring system (Eurocat n°22) annually covers 23,000 births. All the genetic services are delivered by only one genetic center located in Marseilles, and the data collected are computerized. The comparison of these two data bases gives an opportunity to estimate the rate of genetic counseling attendance after the occurrence of an affected stillbirth or live birth. Among the parents of 358 infants born in 1983–84 in this area with a pathology requiring genetic counseling, 226 (63 per cent) attended the Genetic Center within the first year after birth. The rate of attendance is statistically higher (p < 0.01) for the parents who had a stillbirth (78 per cent) than for those who had a live birth (57 per cent). It is also higher (p < 0.01) for the Marseilles maternities group (68 per cent) than for the group outside Marseilles (50 per cent). The referral delays are also analyzed according to malformation etiology and to viability of the child by the eighth day of lue. Besides evaluating a particular genetic center's effectiveness in diffusing information to the public concerned, this work shows that couples’ request is strongly dependent on a psychological need.     

Relationships between pregnancy spacing,sex of infants,maternal age,and birth order,and neonatal and post‐neonatal mortality in Bangladesh

Abstract

The relationships between length of the interpregnancy interval, outcome of the pregnancy preceding the interval, sex of the infants, pregnancy order, maternal age, and maternal history of previous child deaths and neonatal and postneonatal mortality were explored in a rural Bangladeshi population using a multiple regression analysis. Specific interactions between the interpregnancy interval, outcome of the pregnancy preceding the interval, sex of the infants, and history of previous child deaths were examined. An inverse relationship was observed between postneonatal mortality and the length of the interpregnancy interval when the pregnancy preceding the interval was a surviving infant. No such trend was observed for neonatal mortality. Post‐neonatal mortality rates among children whose mothers had experienced two or more previous child deaths were essentially the same as that for infants whose mothers had experienced 0–1 child deaths when the interpregnancy intervals were more than 24 months. Although female infants have a lower neonatal mortality than male infants, the neonatal mortality rate for female infants conceived less than twelve months following a male infant birth was higher than for a male infant conceived less than twelve months following another male infant birth. Post‐neonatal mortality is consistently higher for female compared to male infants in all interval categories.     

Assortative mating in monozygotic twins

Abstract

This study investigated assortative mating in a series of monozygotic twins in terms of anthropométrie variables. Initially the twins were analyzed independent of each other, and the results showed fairly clear homogamy among female MZ twins and their spouses, after correcting for age. Further, when stature was partialled out, several anthropometric measures remained significantly correlated. The results for male MZ twins and their spouses were not nearly so clear‐cut. A second analysis treated the co‐twins together, and once again, the female MZ sets tended to show assortative mate choice for stature while the male MZ twins/spouses were not significantly correlated. A follow‐up analysis investigated whether husbands of the female twins were correlated to each other, and negative results were found for all of the 46 anthropometric variables. An apparent contradiction was resolved in the case of stature by regressing spouse stature against that of the co‐twins. It was found that although each of the twins was assortatively mating, one member of the twin set consistently married a taller husband, but the difference was not constant. This had the effect of producing divergent regression lines.     

Neurological sequelae in twins born after assisted conception: controlled national cohort study

Objective To compare neurological sequelae in twins born after assisted conception with singletons after assisted conception and naturally conceived twins and to assess neurological sequelae in children conceived after in vitro fertilisation (IVF) compared with intracytoplasmic sperm injection (ICSI).Design Controlled, national register based, cohort study.Participants Twins (n = 3393) and singletons (n = 5130) conceived by using assisted reproductive technologies and naturally conceived twins (n = 10 239) born in Denmark between 1995 and 2000. The children''s age at time of follow up was 2-7 years.Data sources Children were identified by cross linkage of the national medical birth registry and the national registry for in vitro fertilisation. Neurological and psychiatric diagnoses were retrieved from the national patients'' registry and the Danish psychiatric central registry.Main outcome measures Neurological sequelae, defined as cerebral palsy, mental retardation, severe mental developmental disturbances, and retarded psychomotor development. Further we made separate analyses on the specific cerebral palsy diagnosis.Results The crude prevalence rates per 1000 of neurological sequelae in twins and singletons after assisted conception and in naturally conceived twins were 8.8, 8.2, and 9.6, and of cerebral palsy 3.2, 2.5, and 4.0, respectively. In twins after assisted conception compared with control twins, the odds ratios of neurological sequelae and specifically of cerebral palsy, adjusted for child sex and year of birth, were 0.9 (95% confidence interval 0.6 to 1.4) and 0.8 (0.4 to 1.6), respectively. The corresponding odds ratios for twins after assisted conception compared with singletons after assisted conception were 1.1 (0.7 to 1.7) for neurological sequelae and 1.3 (0.6 to 2.9) for cerebral palsy. The odds ratio of neurological sequelae in children conceived by ICSI was 0.9 (0.5 to 1.7) ν children conceived by IVF.Conclusions Twins from assisted conception have a similar risk of neurological sequelae as their naturally conceived peers and singletons from assisted conception. Children born after ICSI have the same risk of neurological sequelae as children born after IVF.     

Early sexual maturity among Pumé foragers of Venezuela: fitness implications of teen motherhood

Because humans have slow life histories, discussions of the optimal age at first birth have stressed the benefits of delayed reproduction. However, given the diversity of ecological, fertility, and mortality environments in which humans live, reproductive maturity is expected to be highly variable. This article uses reproductive histories to examine a pattern of early menarche and first birth among the Pume, a group of South American foragers. Age at menarche and first birth are constructed using both retrospective and cross‐sectional data for females over the age of 10 (n = 83). The objectives are first to define these patterns and then discuss their reproductive consequences. On average, Pume girls reach menarche at age 12.9, and give birth to their first child at age 15.3–15.5 (retrospective and cross‐sectional data, respectively). This populational average falls several years prior to what often is considered the human norm. Two questions are then considered. What are the infant mortality costs across a mother's reproductive career? How does surviving fertility vary with age at first birth? Results indicate that the youngest of first‐time mothers (<14) are four times more likely to loose their firstborns than older first‐time mothers (≥17). Given parity‐specific mortality rates, the optimal strategy to minimize infant mortality and maximize reproductive span is to initiate childbearing in the midteens. Women gain no additional advantage in surviving fertility by delaying childbearing until their late teens. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.     

Causes of low utilization of amniocentesis by women of advanced maternal age

Abstract

The objectives of this study were to determine current usage of amniocentesis by women of advanced maternal age in a southwestern Ohio county and to determine potential usage levels by surveying women not utilizing the procedure to understand their reasons. For women age 35 and older giving birth in Hamilton County, Ohio, the estimated percentage using amniocentesis was 3.9 in 1978, 7.6 in 1979, and 13.3 in 1980. Approximately comparable statewide utilization rates were 7.0, 11.5, and 17.2 respectively. A telephone survey during the summer of 1980 of 81 Hamilton County women age 35 and older recently giving birth to a normal baby found four main reasons why they did not utilize amniocentesis: (1) they did not feel at an increased risk (29.6 per cent); (2) they had never heard of the test (24.7 per cent); (3) they were opposed to abortion (21.0 per cent); and (4) no one suggested they have the test done (19.8 per cent). Their physicians reported that 81 per cent of these women had received prenatal counseling. Thus, of those counseled, over two‐thirds apparently missed at least one essential message of the counseling they were presumably provided. These findings, coupled with 47.7 per cent of women who knew about amniocentesis saying they would most likely use it if they became pregnant again and their physician recommended it, indicate that utilization of prenatal diagnosis by at least 50 per cent of women age 35 and older is likely with greater public education and greater support of the procedure by obstetricians.     

Mortality among twins after age 6: fetal origins hypothesis versus twin method.

OBJECTIVE--To test the validity of the fetal origins hypothesis and the classic twin method. DESIGN--Follow up study of pairs of same sex twins in which both twins survived to age 6. SETTING--Denmark. SUBJECTS--8495 twin individuals born 1870-1900, followed through to 31 December 1991. MAIN OUTCOME MEASURES--Mortality calculated on a cohort basis. RESULTS--Mortality among twins and the general population was not significantly different except among females aged 60-89, in whom mortality among twins was 1.14 times (SE 0.03) higher than in the general population. Mortality among female dizygotic twins was 1.77 times (0.18) higher than among monozygotic twins at age 30-59. Otherwise, mortality for monozygotic and dizygotic twins did not consistently differ after age 6. CONCLUSION--According to the fetal origins hypothesis the risk of adult morbidity and mortality is heightened by retardation in intrauterine growth. Twins, and in particular monozygotic twins, experience growth retardation in utero. The findings in the present study suggest that the fetal origins hypothesis is not true for the retardation in intrauterine growth experienced by twins. Furthermore, the data are inconsistent with the underlying assumption of a recent claim that the classic twin method is invalid for studies of adult diseases. The present study is, however, based on the one third of all pairs of twins in which both twins survived to age 6. The possible impact of this selection can be evaluated in future studies of cohorts of younger twins with lower perinatal and infant mortality.     

Predicted birthweight for singletons and twins.

This population-based study determined the impact of co-twin gender on twin intrauterine growth in addition to their infant gender, maternal height, maternal age and parity on intrauterine growth rate of singletons and twins. All singletons and twins born in Western Australia during the period of 1980 to 1995 were considered for the study. The multiple linear regression models showed that 76% of the variance in the mean birthweight was explained by the selected variables for twins and 51% for singletons. Twins grew more slowly than singletons from 26 weeks gestation. Among twins, opposite-sex twin pairs grew consistently faster than like-sex twins. Primiparous twin pairs grew more slowly than subsequently born twins. These regression equations can be used to assess the appropriateness of intrauterine growth in twin pairs of various gender combinations.