Aetiology and classification of small for gestational age infants

Maternal smoking during pregnancy and the risk of congenital urogenital malformations: A systematic review and meta-analysis

BACKGROUND

Investigations regarding the association between maternal smoking and specific urogenital teratogenesis exist. However, an integrated systematic review and meta-analysis studying the relationship by encompassing the whole urogenital system is essential.

OBJECTIVE

Even though many studies about inborn urogenital malformations have been conducted, its etiologic factors and exact pathogenesis are still unclear. Our aim is to assess the risk of congenital urogenital malformations in offspring of smoking pregnant women.

RESULTS

The meta-analysis, covering 41 case-control and 11 cohort studies, suggested that maternal smoking was associated with an increased risk of urogenital teratogenesis (odds ratio [OR] = 1.13, 95% confidence interval [CI]: 1.04-1.23, p = 0.005), cryptorchidism (OR = 1.18, 95%CI: 1.12-1.24, p = 0.0001), hypospadias (OR = 1.16, 95%CI: 1.01-1.33, p = 0.039), and kidney malformations (OR = 1.30, 95%CI: 1.14-1.48, p = 0.0001). Moreover, paternal smoking during the mother's pregnancy was also significantly associated (OR = 1.26, 95%CI: 1.03-1.55, p = 0.028). The association between smoking > 10 cigarettes/day was evident but was not significant (OR = 1.24, 95%CI:0.81-1.88, p = 0.323).

CONCLUSION

Our results showed that maternal smoking during pregnancy increased the risk of congenital urogenital malformations. In numerous epidemiological studies, maternal smoking during pregnancy has a significant role in fetal development. Therefore, quitting tobacco use may be an effective method for reducing the risk of congenital urogenital malformation in pregnant women.

The Cumulative Risk of Chemical and Nonchemical Exposures on Birth Outcomes in Healthy Women: The Fetal Growth Study

Metals, stress, and sociodemographics are commonly studied separately for their effects on birth outcomes, yet often jointly contribute to adverse outcomes. This study analyzes two methods for measuring cumulative risk to understand how maternal chemical and nonchemical stressors may contribute to small for gestational age (SGA). SGA was calculated using sex-specific fetal growth curves for infants of pregnant mothers (n = 2562) enrolled in the National Institute of Child Health and Human Development (NICHD) Fetal Growth Study. The exposures (maternal lead, mercury, cadmium, Cohen's perceived stress, Edinburgh depression scores, race/ethnicity, income, and education) were grouped into three domains: metals, psychosocial stress, and sociodemographics. In Method 1 we created cumulative risk scores using tertiles. Method 2 employed weighted quantile sum (WQS) regression. For each method, logistic models were built with three exposure domains individually and race/ethnicity, adjusting for age, parity, pregnancy weight gain, and marital status. The adjusted effect of overall cumulative risk with three domains, was also modeled using each method. Sociodemographics was the only exposure associated with SGA in unadjusted models ((odds ratio) OR: 1.35, 95% (confidence interval) CI: 1.08, 1.68). The three cumulative variables in adjusted models were not significant individually, but the overall index was associated with SGA (OR: 1.17, 95% CI: 1.02, 1.35). In the WQS model, only the sociodemographics domain was significantly associated with SGA. Sociodemographics tended to be the strongest risk factor for SGA in both risk score and WQS models.

Prenatal depression and adverse birth outcomes: an updated systematic review

Complications related to preterm birth (PTB) and low birth weight (LBW) are leading causes of infant morbidity and mortality. Prenatal depression is a hypothesized psychosocial risk factor for both birth outcomes. The purpose of this systematic review was to examine evidence published between 1977 and 2013 on prenatal depression and risks of these primary adverse birth outcomes. A systematic search of the PUBMED and PsycINFO databases was conducted to identify studies testing the associations between prenatal depressive symptoms, or diagnoses of depression, and risk of PTB or LBW. We systematically selected 50 published reports on PTB and length of gestation, and 33 reports on LBW and BW. Results were reviewed by two independent reviewers and we evaluated the quality of the evidence with an established systematic review method, the Newcastle Ottawa Scale. We then undertook a narrative synthesis of the results following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Less than a quarter of 50 published reports found that prenatal depression was significantly associated with PTB or gestational age. In contrast, slightly more than half of the 33 reports found that prenatal depression was associated with LBW or BW. When weighing methodological features, we determined that the effects of prenatal depression on LBW are more consistent than effects on length of gestation or PTB. Although the evidence may not be strong enough to support routine depression screening for risk of adverse outcomes, screening to enable detection and timely treatment to reduce risk of postpartum depression is warranted. Further rigorous research on prenatal depression and adverse birth outcomes is needed.

Risk factors for preterm birth and small-for-gestational-age births among Canadian women

BACKGROUND

Preterm births (PTB) and small-for-gestational-age (SGA) births are distinct but related pregnancy outcomes, with differing aetiologies and short and long-term morbidities. Few studies have compared a broad array of predictors among these two outcomes. The purpose of this study was to compare risk factors for PTB and SGA births using a national sample of Canadian women.

METHODS

We analysed data from the Canadian Maternity Experiences Survey (n = 6421). Mothers were ≥ 15 years of age, gave birth to a singleton infant and were living with their infant at the time of the interview (between 5 and 14 months post-partum). Backward stepwise multivariable logistic regression models were constructed for each outcome.

RESULTS

Risk profiles for the two outcomes had both differences and similarities. Risk factors specific to PTB were education less than high school, having a previous medical condition, developing a new medical condition or health problem during pregnancy, being a primigravida, or being a multigravida with a previous PTB or a previous miscarriage or abortion. Risk factors unique to SGA were low pre-pregnancy body mass index (<18 kg/m(2) ), smoking during pregnancy and being a recent immigrant. Risk factors for both outcomes included low weight gain during pregnancy (<9.1 kg), short stature (<155 cm) and reporting life as 'very stressful' in the year prior to birth of the baby.

CONCLUSION

A greater understanding of the risk factors related to PTB and SGA may help to reduce the prevalence of these conditions and the associated risk of infant mortality and morbidity.

Life course variation in the relation between maternal marital status and preterm birth

PURPOSE

Maternal marriage is protective against preterm birth (PTB), whereas advanced maternal age is associated with increased PTB risk. Because relations between social factors and health may vary during the life course, we assessed how the relation between marital status and PTB risk may change with maternal age.

METHODS

We assessed the interaction between marital status and maternal age as a determinant of PTB among all live singleton births in Michigan between 1995 and 2006. We also fit stratified models by race. We calculated absolute differences in predicted PTB as well as odds ratios of PTB by marital status for each age group.

RESULTS

In adjusted models, there was a significant interaction (p(interaction)<.001) between marital status and maternal age. The predicted probability of PTB by marital status was marginally different among mothers ages 20-25 years (absolute difference of 1.5%); this difference was substantially greater (3.9% or greater) after 31 years of age. Odds of PTB followed a similar trajectory. Findings were similar among black and white mothers.

CONCLUSIONS

The relationship between marriage and PTB may vary with maternal age suggesting that the influence of social factors on risk for adverse birth outcomes may differ through the maternal life trajectory. We discuss plausible explanations for these findings.

Changes in the relationship between marriage and preterm birth, 1989-2006

OBJECTIVE

Maternal marriage has historically been protective against preterm birth (PTB); however, social norms and behaviors surrounding marriage have changed over time in the United States. We analyzed secular trends in the relationship between marriage and PTB.

METHODS

We collected data about all births in Michigan between 1989 and 2006 to assess (1) the relationship between marital status and PTB and moderately PTB risk by year, and (2) the relationship between married and unmarried status and PTB and moderately PTB by year relative to similar marital status in 1989.

RESULTS

Among nearly 2.4 million births between 1989 and 2006, PTB risk among married mothers increased while risk among unmarried mothers decreased. In adjusted models, married status became less protective against PTB relative to unmarried status over time by year, and was associated with higher risk of PTB over time. Moderately PTB risk increased among both married and unmarried groups, but more so among married mothers.

CONCLUSION

Our findings suggest that marriage is becoming less protective against PTB over time. The influence of social factors on risk for adverse birth outcomes is likely dynamic, suggesting that ongoing revisions to our understanding are in order.

Academic, social, and behavioral outcomes at age 12 of infants born preterm

The effects of gradient levels of perinatal morbidity on school outcomes have been investigated at age 12 in four preterm groups, classified as healthy (no medical or neurological illness), medical morbidity, neurological morbidity, and small-for-gestational-age (SGA), and a full-term comparison group. Teachers report on academic competence, social skills, and problem behaviors. Data on school type, classroom setting, and school service use are gathered from school records. Preterm groups are found to be equivalent to full-term peers in social skills and problem behavior. Preterm groups with neurological and SGA morbidity have the lowest academic competence scores. Unexpectedly, preterm infants with medical morbidity have higher academic competence scores compared with the other preterm groups. School service use increases with greater perinatal morbidity and is contingent on multiple rather than single indicators of perinatal morbidity. Continued monitoring of preterm infants through early adolescence will ensure that appropriate school services and resources are available to maximize their school success.

Smoking habits, nicotine use, and congenital malformations

OBJECTIVE

We examined whether maternal smoking and use of nicotine substitutes during the first 12 weeks of pregnancy increased the prevalence of congenital malformations in general and of certain congenital malformations in particular.

METHODS

In the Danish National Birth Cohort (1997-2003) we identified 76,768 pregnancies (and their subsequent singleton births); 20,603 were exposed to tobacco smoking during the first 12 weeks of pregnancy. Birth outcomes were collected by linkage to the Central Population Register, the National Patients Register, and the National Birth Register. We identified congenital malformations from the Hospital Medical Birth Registry as they were recorded at birth or in the first year of follow-up.

RESULTS

Smoking mothers were younger, weighed less, consumed more alcohol, and had received less education. Children exposed to prenatal tobacco smoking had no increase in congenital malformations prevalence compared with the nonexposed children in both crude and adjusted analyses. Children born to nonsmokers, but who used nicotine substitutes, had a slightly increased relative congenital malformations prevalence ratio; relative prevalence rate ratio was 1.61 (95% confidence interval 1.01-2.58), which represents a 60% increased risk. When the analysis was restricted to musculoskeletal malformations, the relative prevalence rate ratio was 2.63 (95% confidence interval 1.53-4.52).

CONCLUSION

Our results showed no increase in congenital malformations related to prenatal tobacco smoking. However, we identified an increase of malformations risk in nonsmokers using nicotine substitutes. This finding needs to be replicated in other data sources.

LEVEL OF EVIDENCE

II-2.

Does unemployment in family affect pregnancy outcome in conditions of high quality maternity care?

Background

The influence of unemployment in the family on pregnancy outcome is controversial. Only a few studies have involved investigation of the effect of unemployment of the father on pregnancy. The objective of this study was to assess the effects of unemployment of one or both parents on obstetric outcome in conditions of free antenatal care attended by the entire pregnant population.

Methods

The data of 24 939 pregnancies included maternal risk factors, pregnancy characteristics and outcome, and was based on a self administered questionnaire at 20 weeks of pregnancy and on clinical records.

Results

Unemployment was associated with adolescent maternal age, unmarried status and overweight, anemia, smoking, alcohol consumption and prior pregnancy terminations. Multivariate logistic regression analysis indicated that after controlling for these maternal risk factors small differences only were found in pregnancy outcomes between unemployed and employed families. Unemployed women had significantly more often small-for-gestational-age (SGA) infants, at an OR of 1.26 (95% CI: 1.12 – 1.42) whereas, in families where both parents were unemployed, the risk of SGA was even higher at an OR of 1.43 (95% CI: 1.18 – 1.73). Otherwise, pregnancy outcome was comparable in the groups studied.

Conclusion

Free antenatal care was unable to fully overcome the adverse pregnancy outcomes associated with unemployment, SGA risk being highest when both parents are unemployed.

Marriage still protects pregnancy

OBJECTIVE

To assess the risk factors and outcome of pregnancy outside marriage in the 1990s, in conditions of a high percentage of extramarital pregnancies and high standard maternity care, used by the entire pregnant population.

DESIGN

Hospital-based cohort study.

SETTING

A university-teaching hospital in Finland.

POPULATION

The 25,373 singleton pregnancies of known marital and cohabiting status.

METHODS

Odds ratios (ORs) with 95% confidence intervals were calculated to estimate the effect of extramarital childbearing on pregnancy outcome. Multiple logistic regression analyses were conducted to control for confounding maternal risk factors.

MAIN OUTCOME MEASURES

Small-for-gestational age (SGA) infants, preterm birth (less than 37 completed weeks), low birthweight (LBW; under 2500 g).

RESULTS

Of the study population, 67.5% were married and 32.5% were unmarried; 24.2% of all mothers were cohabiting. Unmarried status was strongly associated with social disadvantage and particular risk factors, specifically unemployment, smoking and previous pregnancy terminations, which in turn had an impact on obstetric outcome. There were significantly more SGA infants among unmarried mothers (P < 0.001), with an absolute difference of 45%; more preterm deliveries (P= 0.001), with an absolute difference of 17.5%; and more LBW infants (P < 0.001), with an absolute difference of 26%. The differences in adverse pregnancy outcomes between study groups (i) all unmarried women, (ii) cohabiting women and (iii) single women, remained significant after multivariate analysis at adjusted ORs of 1.11, 1.11 and 1.07 for SGA, 1.17, 1.15 and 1.21 for LBW and 1.15, 1.15 and 1.29 for the preterm births, respectively.

CONCLUSION

Even in the 1990s when cohabitation was already common, pregnancy outside marriage was associated with an overall 20% increase of adverse outcomes, and free maternity care did not overcome the difference.

Learning, cognitive, and attentional problems in adolescents born small for gestational age

OBJECTIVE

To determine whether the presence, severity, or symmetry of growth restriction in term infants is an independent risk factor for learning, cognitive, and attentional problems in adolescence.

METHODS

A total of 7388 term infants have been followed prospectively since birth. At 14 years, 5059 mothers completed a Child Behavior Checklist and provided information on their child's school progress. A total of 5051 adolescents completed a Youth Self Report, with 3703 also undergoing psychometric testing with Ravens Progressive Matrices and Wide Range Achievement Test (WRAT) reading subtest. Outcomes were compared on the basis of birth weight groups and measures of body symmetry and were adjusted for the level of social risk at birth.

RESULTS

Adolescents who were born small for gestational age (SGA), when compared with their appropriately grown counterparts (>10th percentile), were more likely to experience learning difficulties, with a higher prevalence in those of birth weight < or =3rd percentile. Girls of birth weight < or =3rd percentile were more likely to have attentional problems and low WRAT reading scores. There was no significant difference in Ravens IQ or mean WRAT reading scores between SGA and non-SGA groups. There was no association between body symmetry and any of the outcomes studied.

CONCLUSIONS

SGA status seems to have only modest independent effects on learning, cognition, and attention in adolescence. Severity but not symmetry of growth restriction predicted learning difficulties.

Benn Index at birth is associated with postnatal linear growth

While previous research has suggested that body thinness is related to subsequent linear growth in children, it is unclear whether thinness at birth is related to linear growth in newborns and catch-up growth in small-forgestational age newborns. Drawing on data from a longitudinal growth study of 3,650 full-term Swedish babies, this study examines linear growth from birth to 6 months of age in three groups of newborns with short (< -2 SDS), appropriate (-2 to 2 SDS) and long (> 2 SDS) body length for gestational age. Among infants short at birth, the Benn Index (kg/m2.69) at birth was not related to the odds of short stature (< -2 SDS) at age 6 months (odds ratio = 1.03; p > 0.10). Nonetheless, the Benn Index was positively related to growth velocity in the first 6 months of life in the short (p = 0.060), appropriate (p < 0.05), and tall (p < 0.05) for gestational age newborns. Use of the Ponderal Index (kg/m3) would give similar results. The findings suggest that nutritional status at birth is related to linear growth velocity in newborns.

Nutritional factors that affect the postnatal metabolic adaptation of full-term small- and large-for-gestational-age infants

OBJECTIVE

To document metabolic adaptation to ex utero life in small- (SGA) and large-for-gestational-age (LGA) infants in relation to fetal nutrition and postnatal feeding practices.

METHODS

In a prospective study, 65 SGA (< or = second centile) and 39 LGA (> or = 98th centile) full-term infants were recruited. Anthropometry was performed within the first 48 hours. There was full support of breastfeeding and close clinical observation. Blood glucose and ketone body (kb) concentrations were measured prefeed for the first 7 postnatal days. Infants were exclusively breastfed (BF), breastfed with formula milk supplementation (FS), or exclusively formula milk fed (FF).

RESULTS

Within the SGA group, a measure of "thinness," the midarm circumference/head circumference ratio, was significantly correlated to the number of episodes of blood glucose < 2.00 mmol/L. Epoch (age at sampling) analysis in this group showed no difference in blood glucose levels across the different feeding groups but revealed a statistically significant greater kb concentration for infants who were exclusively breastfed. For SGA infants, the median peak kb concentration (peak kb) was significantly different for BF, FS, and FF groups. Multiple regression analysis for the SGA group demonstrated that peak kb concentration was negatively related to the volume of formula milk, independent of blood glucose levels and neonatal anthropometry. For LGA infants, low blood glucose levels were offset by kb concentrations equivalent to those observed in infants who were appropriate for gestational age.

CONCLUSION

Neonatal ability to generate kb when blood glucose values are low depends more on successful breastfeeding than on size for gestational age or neonatal nutritional status. Routine blood glucose monitoring of LGA infants with no additional risk factors is not necessary. Routine formula milk supplementation for LGA and SGA infants should not be recommended.

Behavior in term, small for gestational age preschoolers

AIMS

To evaluate whether being born small for gestational age (SGA) was associated with an increased frequency of preschool behavioral problems.

STUDY DESIGN

Follow-up study at 5 years of age.

SUBJECTS

A population based cohort of 318 term infants who were SGA, defined as having a birthweight less than the 15th percentile for gestational age, and without major handicap such as cerebral palsy or mental retardation, and a random control sample of 307 appropriate for gestational age (AGA) infants.

OUTCOME MEASURES

The Personality Inventory for Children and the Yale Children's Inventory (completed by the mothers), and child behavior during psychometric testing.

RESULTS

Behavior problems was not more common among the SGA children. The results were not confounded by a wide range of parental demographic and child rearing factors, including maternal non-verbal problem solving abilities, child rearing style, and maternal psychological distress. However, the parental factors explained 13% of the variance in a summary score of child behavior compared to 1% explained by SGA vs. AGA status. The SGA children were not more sensitive to the negative impacts of parental risk factors than AGA controls. The study does not address the outcome of severely growth-retarded SGA infants.

CONCLUSION

Being born moderately SGA is not a significant risk factor for preschool behavior problems.

Maternal cigarette smoking during pregnancy and infant ponderal index at birth in the Swedish Medical Birth Register, 1991-1992

OBJECTIVES

This study examined the effect of maternal smoking during pregnancy on infant body proportion.

METHODS

The ponderal index, defined as birthweight divided by crown-heel length cubed, was examined in 207,607 infants from the Swedish Medical Birth Register for 1991 and 1992.

RESULTS

Infant ponderal index was used as the outcome variable in an ordinary least squares continuous regression, which included early pregnancy smoking status, gestational age, and birthweight among the predictors. Ponderal index increased by 0.030 (+/- 0.0014) among infants of moderate smokers and by 0.040 (+/- 0.0017) among infants of heavy smokers, showing a dose response.

CONCLUSIONS

Smoking differentially alters the trajectory of weight vs length growth in the fetus.