Differences in the epidemiology of prematurity and intrauterine growth retardation

Effects of national smoke-free legislation on the rates of preterm births and low birthweights in Taiwan

This study evaluated the effects of partial and complete island-wide smoking bans on perinatal outcomes in Taiwan. Trends were determined in the yearly prevalence rates for preterm births and low birth weight (LBW) for a 1978 to 1997 pre-ban period, a 1998 to 2008 Phase 1 partial ban period, and a 2009 to 2016 Phase 2 complete ban period. Poisson regression with a yearly time-series model was employed to determine alterations in trends in prevalence rates for preterm births and LBW. Compared with pre-ban period, the rate ratio (RR) for Phase 1 preterm births was 0.969 (95% confidence interval [CI] = 0.968-0.971) and Phase 2 0.995 (95% CI = 0.992-0.998). The Phase 1 RR LBW fell 0.4% (95% CI = 0.2%-0.5%), but Phase 2 RR rose 1.7% (95% CI = 1.4%-2.1%). Data indicated that the risk of preterm births and LBW in Taiwan was reduced significantly after implementation of the smoking ban. These findings are in agreement with growing evidence suggesting that smoke-free legislation exerted a beneficial health effect on pregnant women and their newborn infants.

The nutritional consequences of pregnancy sickness : A critique of a hypothesis

The purpose of this paper is to assess Profet's (1992) and others' hypothesis that nausea and vomiting in pregnancy (NVP) is adaptive. A number of studies have found an association between NVP and a decreased risk for early fetal loss (<20 weeks). It is assumed that the adaptive benefits of improved survivorship associated with NVP outweigh the minimal nutritional consequences. However, in populations that experience marginal levels of nutrition, NVP may have important nutritional consequences. To test these potential consequences, a study on NVP, nutritional status, and pregnancy outcome was conducted among Turkana pastoralists, who experience seasonal and chronic nutritional stress. Interviews and anthropometric assessments were conducted on 68 pregnant Turkana women of Kenya during a 1993-1994 field season. The results from the case study suggest that women who experience NVP do encounter nutritional consequences in the later stages of pregnancy and are more likely to experience poor pregnancy outcomes. These results suggest that NVP may not be adaptive in all environmental settings, particularly among marginally nourished populations.

Low birth weight at term and its determinants in a tertiary hospital of Nepal: a case-control study

Birth weight of a child is an important indicator of its vulnerability for childhood illness and chances of survival. A large number of infant deaths can be averted by appropriate management of low birth weight babies and prevention of factors associated with low birth weight. The prevalence of low birth weight babies in Nepal is estimated to be about 12-32%.Our study aimed at identifying major determinants of low birth weight among term babies in Nepal. A hospital-based retrospective case control study was conducted in maternity ward of Tribhuvan University Teaching Hospital from February to July 2011. A total of 155 LBW babies and 310 controls were included in the study. Mothers admitted to maternity ward during the study period were interviewed, medical records were assessed and anthropometric measurements were done. Risk factors, broadly classified into proximal and distal factors, were assessed for any association with birth of low-birth weight babies. Regression analysis revealed that a history of premature delivery (adjusted odds ratio; aOR5.24, CI 1.05-26.28), hard physical work during pregnancy (aOR1.48, CI 0.97-2.26), younger age of mother (aOR1.98, CI 1.15-3.41), mothers with haemoglobin level less than 11gm/dl (aOR0.51, CI0.24-1.07) and lack of consumption of nutritious food during pregnancy (aOR1.99, CI 1.28-3.10) were significantly associated with the birth of LBW babies. These factors should be addressed with appropriate measures so as to decrease the prevalence of low birth weight among term babies in Nepal.

Impact of a stepwise introduction of smoke-free legislation on the rate of preterm births: analysis of routinely collected birth data

OBJECTIVE

To investigate the incidence of preterm delivery in the Belgian population after implementation of smoke-free legislation in three phases (in public places and most workplaces January 2006, in restaurants January 2007, and in bars serving food January 2010).

DESIGN

Logistic regression analyses on routinely collected birth data from January 2002 to December 2011.

SETTING

Flanders, Belgium.

POPULATION

All live born singleton births delivered at 24-44 weeks of gestation (n = 606,877, with n = 448,520 spontaneous deliveries).

MAIN OUTCOME MEASURES

Preterm birth (gestational age <37 weeks).

RESULTS

We found reductions in the risk of preterm birth after the introduction of each phase of the smoking ban. No decreasing trend was evident in the years or months before the bans. We observed a step change in the risk of spontaneous preterm delivery of -3.13% (95% CI -4.37% to -1.87%; P<0.01) on 1 January 2007 (ban on smoking in restaurants), and an annual slope change of -2.65% (-5.11% to -0.13%; P=0.04) after 1 January 2010 (ban on smoking in bars serving food). The analysis for all births gave similar results: a step change of -3.18% (-5.38% to -0.94%; P<0.01) on 1 January 2007, and an annual slope change of -3.50% (-6.35% to -0.57%; P=0.02) after 1 January 2010. These changes could not be explained by personal factors (infant sex, maternal age, parity, socioeconomic status, national origin, level of urbanisation); time related factors (underlying trends, month of the year, day of the week); or population related factors (public holidays, influenza epidemics, and short term changes in apparent temperature and particulate air pollution).

CONCLUSION

Our study shows a consistent pattern of reduction in the risk of preterm delivery with successive population interventions to restrict smoking. This finding is not definitive but it supports the notion that smoking bans have public health benefits from early life.

Maternal supplementation differentially affects the mother and newborn

Although studying the effect of supplementation on maternal health or the outcome of pregnancy was not a primary goal of the Institute of Nutrition of Central America and Panama Oriente Longitudinal Study, many important findings in these areas were produced. As part of the study, a food supplementation program was implemented. Two villages received Atole, a gruel containing protein and energy, and 2 matched villages received a refreshing, low-energy drink containing no protein. Both drinks contained micronutrients. Some women did not choose to consume the supplements and those who did consumed widely varying amounts. More volume of Fresco was consumed than Atole. The energy in the supplements improved birthweight, with no apparent additional benefit from protein or micronutrients. Researchers identified several groups of women who benefited from supplementation more than others by having babies with higher birthweights, including those with poorer current nutritional status and those who consumed high amounts of the supplement continuously from one pregnancy to the next. Results from the study provided an early indication that supplementation might increase the duration of gestation and, thus, reduce preterm birth. On the other hand, maternal supplementation did not substantially alter the duration of postpartum amenorrhea once concurrent infant supplementation was taken into account. Finally, findings from this study provided evidence of a biological trade-off between maintenance of maternal nutritional status and increasing fetal size that was responsive to both current maternal nutritional status and supplement intake but not to the mother's nutritional status earlier in life.

Prenatal therapy for fetal growth restriction

The choice of therapy for fetal growth restriction (FGR) depends on the nature of the insult that led to the development of FGR. Many etiologic factors are either not amenable to therapy or fetal growth has not been improved by treatments that benefit the mother. Many therapeutic approaches have been used to improve fetal condition. None of the approaches have been of value in a consistent manner. We present the numerous approaches, and their rationale for their use, that have been tried to treat the growth impaired fetus. The evidence from the randomized clinical trials is summarized and their conclusions given.

Air pollution and very low birth weight infants: a target population?

OBJECTIVE

The goal was to examine systematically the association between maternal exposure to particulate matter of <10 microm and very low birth weight (<1500 g) delivery for evidence of an effect on duration of gestation and/or intrauterine growth restriction.

METHODS

This case-control study took place between April 1, 1986, and March 30, 1988, in Georgia Health Care District 9 and included 128 mothers of very low birth weight infants, all of whom were preterm and were classified as either small for gestational age or appropriate for gestational age, and 197 mothers of term, appropriate-for-gestational-age infants weighing > or = 2500 g. Maternal exposure to particulate matter of <10 microm was estimated with 2 exposure measures, namely, a county-level measure based on residence in a county with an industrial point source and an environmental transport model based on the geographic location of the birth home.

RESULTS

Considering preterm/appropriate-for-gestational-age infants as cases and term/appropriate-for-gestational-age infants as controls, adjusted odds ratios for maternal exposure to particulate matter of <10 microm were statistically significant (adjusted odds ratio for county-level model: 4.31; adjusted odds ratio for environmental transport model: 3.68). Although elevated, no statistically significant association was found between maternal exposure and preterm/appropriate-for-gestational-age delivery when compared to preterm/small-for-gestational-age delivery.

CONCLUSIONS

There are increased odds of maternal exposure to ambient particulate matter of <10 microm for very low birth weight preterm/appropriate-for-gestational-age delivery, compared with term/appropriate-for-gestational-age delivery, which suggests that the observed association between maternal exposure to air pollution and low infant birth weight (particularly <1500 g) is at least partially attributable to an effect on duration of gestation.

The nutrient intakes of mothers of low birth weight babies - a comparison of ethnic groups in East London, UK

The objective of this paper was to compare the nutrient intakes of mothers of different ethnic origins after they had given birth to a low birth weight (LBW) baby (< 2.5 kg). A total of 165 participants from East London, UK completed a prospective 7-day diet diary using household measures, between 8 and 12 weeks post-partum. The data were originally collected as baseline data prior to two separate nutrition intervention studies and were combined and re-interrogated for the purpose of this paper. Folate and iron intakes were low in all ethnic groups compared to the Reference Nutrient Intakes (RNI). Half did not meet the RNI for folate and 88% did not meet the RNI for iron. Nearly a quarter of the group did not achieve the Lower Reference Nutrient Intake (LRNI) for iron. The mean vitamin D and calcium intakes were significantly different between the ethnic groups (P = 0.007, P = 0.001, respectively). African women had the highest vitamin D intakes (4.72 microg d(-1)) and Caucasians and Asians the lowest (2.4 microg d(-1)). Caucasians had the highest calcium intakes (780 mg d(-1)) and Africans the lowest (565 mg d(-1)). Over two-thirds of African, Asian and African-Caribbean women did not meet the RNI for calcium. Thirty-one per cent of Africans did not meet the LRNI for calcium. Our data show a high prevalence of inadequate nutrition among women who deliver LBW babies with differences in nutrient intake between ethnic groups. This information can be used to target specific appropriate dietary advice to ethnic minorities for the prevention or repetition of LBW.

Effects of antenatal multiple micronutrient supplementation on birthweight and gestational duration in Nepal: double-blind, randomised controlled trial

BACKGROUND

Neonatal mortality is the biggest contributor to global mortality of children younger than 5 years, and low birthweight is a crucial underlying factor. We tested the hypotheses that antenatal multiple micronutrient supplementation would increase infant birthweight and gestational duration.

METHODS

We did a double-blind, randomised controlled trial in Dhanusha district, Nepal. Women attending for antenatal care with singleton pregnancies at up to 20 weeks' gestation were invited to participate. Participants were randomly allocated either routine iron and folic acid supplements (control; n=600) or a multiple micronutrient supplement providing a recommended daily allowance of 15 vitamins and minerals (intervention; n=600). Supplementation began at a minimum of 12 weeks' gestation and continued until delivery. Primary outcome measures were birthweight and gestational duration. Analysis was by intention to treat. The study is registered as an International Standard Randomised Controlled Trial, number ISRCTN88625934.

FINDINGS

Birthweight was available for 523/600 infants in the control group and 529/600 in the intervention group. Mean birthweight was 2733 g (SD 422) in the control group and 2810 g (453) in the intervention group, representing a mean difference of 77 g (95% CI 24-130; p=0.004) and a relative fall in the proportion of low birthweight by 25%. No difference was recorded in the duration of gestation (0.2 weeks [-0.1 to 0.4]; p=0.12), infant length (0.3 cm [-0.1 to 0.6]; p=0.16), or head circumference (0.2 cm [-0.1 to 0.4]; p=0.18).

INTERPRETATION

In a poor community in Nepal, consumption of a daily supplement containing a recommended daily allowance of 15 micronutrients in the second and third trimesters of pregnancy was associated with increased birthweight when compared with a standard iron and folic acid preparation. The effects on perinatal morbidity and mortality need further comparisons between studies. Published online March 3, 2005 http://image.thelancet.com/extras/04art11045web.pdf.

Effect of air pollution on preterm birth among children born in Southern California between 1989 and 1993

We evaluated the effect of air pollution exposure during pregnancy on the occurrence of preterm birth in a cohort of 97,518 neonates born in Southern California. We used measurements of carbon monoxide (CO), nitrogen dioxide, ozone, and particulate matter less than 10 microm (PM10) collected at 17 air-quality-monitoring stations to create average exposure estimates for periods of pregnancy. We calculated crude and adjusted risk ratios (RRs) for premature birth by period-specific ambient pollution levels. We observed a 20% increase in preterm birth per 50-microg increase in ambient PM10 levels averaged over 6 weeks before birth [RRcrude = 1.20; 95% confidence interval (CI) = 1.09-1.33] and a 16% increase when averaging over the first month of pregnancy (RRcrude = 1.16; 95% CI = 1.06-1.26). PM10 effects showed no regional pattern. CO exposure 6 weeks before birth consistently exhibited an effect only for the inland regions (RRcrude = 1.13; 95% CI = 1.08-1.18 per 3 parts per million), and during the first month of pregnancy, the effect was weak for all stations (RRcrude = 1.04; 95% CI = 1.01-1.09 per 3 parts per million). Exposure to increased levels of ambient PM10 and possibly CO during pregnancy may contribute to the occurrence of preterm births in Southern California.

The effect of heavy maternal workload on fetal growth retardation and preterm delivery. A study among southern Thai women

Heavy maternal workloads are considered to be hazardous to the fetus. The effects of physical activity during pregnancy on low birth weight (LBW), small for gestational age (SGA), and prematurity were assessed from a sample of 1797 women in a follow-up study at the antenatal clinic of two hospitals in southern Thailand. The women were interviewed twice, at 17 and 32 gestational weeks. Outcome data were obtained from medical records and the newborn gestational age determined using Dubowitz's score. The risk of SGA was elevated for women working > 50 hours/week, squatting in work, commuting > 1 hour/day, and having high psychological job demands; the risk of preterm delivery was increased with obstetrical complications. Women who worked long hours and had demanding work conditions had an elevated risk of giving birth to SGA infants but not of preterm delivery.

The influence of fetal and maternal factors on the distribution of birthweight

This review of common risk factors for low birthweight emphasizes the usefulness of examining the entire distribution of birthweight. Of the factors we examined, only short gestational age seemed to affect the low end of the birthweight distribution in the form of skewness. Most factors, such as maternal race, infant sex, plurality, altitude, education, and smoking seem to affect the entire birthweight distribution, indicating a generalized effect. With the exceptions of race, infant sex, parity, and altitude, these factors seemed to have similar associations with both low birthweight and infant mortality. However, only the effects of race and sex on mortality have been repeatedly studied in detail for different combinations of gestational age and birthweight. A few of the factors examined, notably infant sex and parity, have opposite associations with birthweight and infant mortality. Female infants and firstborn infants have lower birthweights than their counterparts, but are more likely to survive. For factors that significantly affect the birthweight distribution, but do not affect mortality equally across the birthweight distribution, the development and use of population-based standards may result in less misclassification of IUGR. Separate standards by infant sex, altitude, and perhaps race may lead to more accurate classification of intrauterine growth. Last, the majority of risk factors have differential effects on birthweight depending on the level of the associated factors. For example, low maternal age and low prepregnancy BMI are associated with both increased risk of low birthweight and poor infant survival. Older maternal age and high prepregnancy BMI are associated with reduced risk of low birthweight, but with increased risk of infant mortality. One possible explanation is that young maternal age and low prepregnancy BMI are associated with adverse behavioral risk factors such as cigarette smoking, whereas increased age and high prepregnancy BMI are associated with gestational diabetes, multiparity, and genetic defects. It is possible that the greater variation in birthweight at the high end of the scale is indicative of increased risk of mortality. Thus, higher birthweight does not always equal better birth outcomes.

Development of a practical screening tool to identify preterm, low-birthweight neonates in Ethiopia

Preterm, low-birthweight (LBW) newborn infants are at high risk of neonatal mortality and morbidity and need early referral for special paediatric care. In developing countries, birthweight and gestational age often cannot be measured and a practical screening tool based on surrogate neonatal body measurements to identify high-risk infants would be very useful. We studied a consecutive series of 843 singleton infants born at a referral hospital in Addis Ababa, Ethiopia. Gestational age, birthweight, and four body measurements (chest, head, and mid-arm circumferences and length) were accurately recorded. We randomly divided the series into equal-sized training and validation groups. In the training group, we used a recursive partitioning technique to develop a simple predictive algorithm--infants were classified as high risk if head circumference was 31 cm or less or if chest circumference was 30 cm or less, and were classified as low risk otherwise. When tested in the validation group, this algorithm had sensitivity, specificity, and negative predictive value for prediction of preterm and LBW births above 90%. Thus, neonatal body measurements can be combined into a pragmatic, accurate screening tool suitable for clinical use in developing countries.

Gestational age and intrauterine growth retardation among white and black very low birthweight infants: a population-based cohort study

Very low birthweight (VLBW) is a commonly used endpoint in perinatal epidemiology, but the population of VLBW infants comprises a wide range of gestational ages and rates of fetal growth. We used data from a population-based study of all 1072 black and white VLBW liveborn infants born in 29 counties in Georgia between April 1986 and March 1988. Less than 1% of the VLBW infants were > or = 37 weeks gestation; most were 29-32 weeks (26%) or 25 to 28 weeks (40%); 12% were 22 weeks or less. All infants 33 weeks gestation or greater were growth retarded. The population of VLBW infants seems to comprise three groups: approximately 11% very immature infants of 22 weeks or less; the majority of infants, born between 23 and 30 weeks, 90% of which are of normal weight for their gestational age; and a group of less premature, growth-retarded infants from 31 to 36 weeks. We found little or no difference in the distribution of gestational age or the percentage of intrauterine growth rates (IUGR) between black and white infants. In the USA the VLBW rate among black infants is over three times greater than that among white infants and consequently the rates of the three types of VLBW among black infants are likely to be triple those among white infants.

Determinants of neonatal mortality in central Sudan

A follow-up study was conducted in six community health centres during the period April 1989 to March 1990 to determine the risk factors which influence neonatal survival in central Sudan. The estimated neonatal mortality rate ranged between 20.0 and 36.0 per 1000 live births per year, and the major cause of death was tetanus neonatorum (29% of neonatal deaths). The mortality rate was lowest when tetanus toxoid was received during pregnancy and the umbilical cord was cleaned by a modern hygienic method (mortality rate of 11 per 1000). In contrast, the mortality rate was highest when no tetanus toxoid was received and no or traditional cord cleaning was used (mortality rate of 62 per 1000; relative risk (RR) = 5.6, 95% confidence interval (CI) 2.0-14.9). The major predictors of neonatal mortality were tetanus, short birth-to-conception interval, multiparity, reported malaria during pregnancy, low birthweight, low maternal weight and low socio-economic status. The population attributable risks were high, and the preventable factors collectively accounted for 93.5% of neonatal mortality. Safe deliveries and wider immunization coverage are needed to control neonatal tetanus in this community. Other interventions to lower neonatal mortality in central Sudan should include accessible family planning programmes and measures to lower the incidence of low birthweight.

Biological, Nutritional, and Social Factors Associated with Intra-Uterine Growth Retardation in Mexico City

This study investigates the relationship between maternal biological, nutritional, and socio-demographic variables as they relate to intra-uterine growth retardation (IUGR) in 162 women who delivered in a maternal and child centre in Mexico City. Data were obtained through a questionnaire administered to each woman after her infant was born. The mothers’ height, arm and head circumferences, and skinfolds were measured after delivery. Infants were defined as having IUGR if their gestational age was 37 weeks or over and their birth weight was at or below the 10th percentile of a sex-specific birth weight-gestational age distribution of a reference population. Infants whose gestational age was 37 weeks or over and whose birth weight was above the 10th percentile of the reference population distribution were defined as having normal birth weight. Overall, maternal risk factors associated with past and current nutritional status were associated with IUGR, but social factors were not. Logistic regression analysis showed that height, positive dietary changes during pregnancy, and past spontaneous abortions during the second trimester were significantly related to IUGR.

Small-for-gestational-age birth: maternal predictors and comparison with risk factors of spontaneous preterm delivery in the same cohort

Low birth weight, the primary predictor of infant mortality and morbidity, can be a result of shortened gestation (preterm delivery) or fetal growth retardation (small for gestational age). We examined the relationship between maternal characteristics and the risk of delivering a small-for-gestational age infant in 2228 women who participated in the University of California, San Diego Prenatal Nutrition Project between 1978 and 1988. A multivariate analysis indicated that significant risk factors for small for gestational age were cigarette smoking (odds ratio, 3.18), a low rate of maternal weight gain (odds ratio, 2.96), black ethnicity (odds ratio, 2.60), pregravid underweight (odds ratio, 2.36), Asian ethnicity (odds ratio, 1.88), primiparity (odds ratio, 1.85), and low maternal height (odds ratio, 1.63). These findings are contrasted with those previously published on preterm deliveries in the same cohort. We conclude that with the exception of black ethnicity and low maternal weight gain, different maternal characteristics were significantly associated with small-for-gestational-age and preterm birth in this population.

[Health indicators in urban areas. Variations in function of social coherence of the geographic areas used]

The detection of health inequalities in the urban environment and their magnitude depends to a great extent on the internal social coherence of the geographical division used. Using an existing social map of Alicante which divides the city into Basic Units for Social Intervention (BUSI), we have compared the distribution of an indicator with wellknown relationship with the socio-economic level such as Low Birth Weight, using both the BUSI and the municipal districts as analysis units. The data of the newborn were obtained from the records of the Hospital of Alicante corresponding to the years 1985, 1986 and 1987, analysing the 177 Low Birth Weights of the 7,728 born within the period. Using the BUSI we found a dose-response relationship between the socio-economic level and the LBW frequency with a range varying from 86.3 to 123.2. Using the municipal districts, the range varied from 62.5 to 159.6. We conclude that, although the geographical divisions with internal social coherence are better to detect health inequalities, municipal districts can be an analysis unit of easy access and useful for describing inequalities in the cities.

Epidemiological differences among birth weight and gestational age subgroups of newborns

For a sample of 16,113 women who received prenatal care from the Guatemalan Social Security Institute Hospital, we described the distribution of birth weight and gestational age subgroups and the association between known epidemiologic risk factors and the odds for 1) an appropriate-weight-for-gestational-age preterm vs. a small-for-gestational-age term infant, 2) a small-for-gestational-age preterm vs. a small-for-gestational-age term infant, and 3) a normal ponderal index vs. a low ponderal index term small-for-gestational-age infant. We found that low maternal income, education, height (3147 cm), prepregnancy weight (347.8 kg), and weight gain during pregnancy (30.72 kg) were associated with a greater odds for birth of a term small-for-gestational-age infant (particularly those with a normal ponderal index) than for the birth of a preterm appropriate-weight-for-gestational-age infant. Conversely, medical and pregnancy-related complications were associated with greater odds for a preterm birth of an appropriate- or a small-for-gestational-age infant. Implications of these findings for interventions and research are discussed.

The effect of maternal work on fetal growth and duration of pregnancy: a prospective study

The effect on birth outcome of work requiring different degrees of physical exertion was examined among 15,786 pregnant women who were followed through the Guatemalan Social Security Institute's hospital. Work inside and outside the home was ascertained through a questionnaire administered to each women before delivery. Odds ratios were adjusted for household income, maternal height and age, and birthweight of previous infant. Women with three or more children and no household help were at increased risk for small-for-gestational-age (SGA) births compared with women with family (odds ratio (OR) 1.79; 95% confidence interval (CI) 1.31, 2.47) or hired help (OR 2.0; 95% CI 1.16 to 3.33). Compared with office work, manual work increased the risk for an SGA (OR 1.32; 95% CI 1.12 to 1.56) and SGA/preterm birth (OR 2.56; 95% CI 1.10 to 5.96). Work in a standing compared with sitting position significantly increased the risk for a preterm birth (OR 1.56; 95% CI 1.04 to 2.60). There was a significant positive trend in frequency of SGA and SGA/preterm birth with an increase in the physical demands at work, as measured by an activity score. These data suggest that interventions to reduce physical exertion among pregnant women could improve birth outcome.

Comparison of the risk factors for pre-term delivery and intrauterine growth retardation

In a follow-up study of the pregnant women interviewed in the Nutrition Canada survey, we investigated predictors of intrauterine growth retardation (less than or equal to 10th percentile of the birthweight-gestational age distribution for the 1972 Canadian population), and pre-term delivery (less than 37 completed weeks of gestation), by classifying these two endpoints as either small-for-gestational age and not pre-term (SGA-NPT), or not small-for-gestational age but pre-term (NSGA-PT). Education, age, household income level, number of previous livebirths, number of cigarettes smoked per day while pregnant, alcohol consumption (spirits only), serum Vitamin C and haemoglobin levels, pre-pregnancy weight, height, and sex of the infant were related to NSGA-PT deliveries in univariate analyses; serum Vitamin A, smoking history, calorie intake, height and pre-pregnancy weight were similarly associated with the risk of SGA-NPT outcomes. When considered jointly in multivariate logistic regression analysis, however, the significant predictors were reduced to: height and pre-pregnancy weight for SGA-NPT and mother's education, sex of the infant, and household income level for NSGA-PT.

Predicting intrauterine growth retardation in sibships while considering maternal and infant covariates

Data on 6,210 full-term sibships (gestational age greater than 36 weeks) reconstructed from birth certificates registered in Maryland between 1980 and 1984 were used to study sibship aggregation and recurrence risk of intrauterine growth retardation (IUGR) while considering maternal and infant covariates. In this study, IUGR was defined as being below the 10th percentile for race-, sex-, and gestational-age-specific birth weight based on all births registered in Maryland during 1984. Maternal factors (race, age at delivery, marital status, amount of prenatal care, concurrent illnesses, and complications during pregnancy) and infant factors (congenital malformations and first born child or not) were used as covariates in a modified logistic regression model which allowed correlation among sibs. First-time mothers who were under age 30 years, unmarried, received too little prenatal care, or had any reported pregnancy complications were at high risk of delivering an infant with IUGR. Even given the effects of these risk factors, however, there was a significant correlation in risk among full sibs (r = .237 +/- .028), which, combined with information on risk factors, can be used to estimate sibling recurrence risk for IUGR.

Recurrence of low birth weight in siblings

The recurrence of low birth weight (LBW, less than 2500 g) in full siblings was studied in 3286 singleton infants born between 1966 and 1986 to 1677 male U.S. Army veterans who were part of a nationwide health study. Hospital of birth medical records were abstracted for these children. Mean birth weights, risks of LBW, LBW occurring with preterm delivery (less than 37 weeks) (LBW/p), and LBW in term infants (LBW/t) were examined in successive singleton siblings according to LBW status of prior siblings. The risk of LBW in infants who had prior siblings with LBW was 9.9%, compared with a risk of 2.8% in infants who had prior siblings without LBW (OR = 3.8, 95% CI 2.0-7.3). The excess recurrence of LBW was specifically due to LBW/p. Infants with prior siblings with LBW/p were at high tisk of LBW/p (OR = 9.2, CI 4.4-19.6) but not of LBW/t (OR = 2.0, CI 0.1-9.1). Using modified logistic regression techniques that incorporate familial risks and the effects of other risk factors, the excess sibling recurrence risk of LBW and LBW/p could not be explained by the tendency for recurrence in siblings of other risk factors for LBW, such as pregnancy complications, maternal illnesses, and birth defects. Although the familial factors involved in LBW may or may not be genetic in nature, such factors need to be investigated in epidemiologic studies of LBW and prematurity.