D. M. O. Becroft

Risk factors for small-for-gestational-age babies: The Auckland Birthweight Collaborative Study.

Objective: This case‐control study determined whether internationally recognized risk factors for small‐for‐gestational‐age (SGA) term babies were applicable in New Zealand.

Maternal nutritional risk factors for small for gestational age babies in a developed country: a case-control study

Aims: To assess the effect of maternal diet during pregnancy on the risk of delivering a baby who is small for gestational age (SGA). Methods: Case-control study of 844 cases (SGA) and 870 controls (appropriate size for gestational age (AGA)). Only term (37+ completed weeks of gestation) infants were included. Retrospective food frequency questionnaires were completed at birth on the diet at the time of conception and in the last month of pregnancy. Results: At the time of conception, mothers of AGA infants ate significantly more servings of carbohydrate rich food and fruit, and were more likely to have taken folate and vitamin supplements than mothers of SGA infants. There was some evidence that mothers of AGA infants also ate more servings of dairy products, meat, and fish (0.05 < p < 0.1). However, after adjustment for maternal ethnicity, smoking, height, weight, hypertension, and occupation, fish intake (p  =  0.04), carbohydrate-rich foods (p  =  0.04), and folate supplementation (p  =  0.02) were associated with a reduced risk of SGA. In the last month of pregnancy, only iron supplementation was associated with a reduced risk of SGA (p  =  0.05) after adjustment for potential confounders. Conclusions: This study suggests that small variations in maternal diets within the normal range during pregnancy in developed countries are associated with differences in birth weight.

Smoking, nicotine and tar and risk of small for gestational age babies

Aims: To assess the effect of maternal smoking and environmental tobacco smoke (ETS) on risk of small for gestational age infants (SGA). Methods: Case‐control study of 844 cases and 870 controls. Results: Maternal smoking in pregnancy was associated with an increased risk of SGA (adjusted odds ratio (OR) = 2.41; 95% confidence interval (CI) = 1.78, 3.28). We could not detect an increased risk of SGA with paternal smoking, or with other household smokers when the mother was a non‐smoker, but did find an increased risk with exposure to ETS in the workplace or while socializing. Infants of mothers who ceased smoking during pregnancy were not at increased risk of SGA, but those who decreased but did not stop remained at risk of SGA. There was no evidence that the concentration of nicotine and tar in the cigarettes influenced the risk of SGA.

Breastfeeding and intelligence of preschool children

AIM To investigate whether breastfeeding during infancy is a determinant of intelligence at 3.5 y. METHODS Five hundred and fifty European children enrolled at birth in the Auckland Birthweight Collaborative Study were assessed at 3.5 y of age. Approximately half were small for gestational age (SGA < or =10th percentile) at birth and half were appropriate for gestational age (AGA >10th percentile). Duration of breastfeeding was recorded at maternal interview, and the intelligence of children was assessed using the Stanford Binet Intelligence Scale. Regression analysis was used to calculate estimates of difference in intelligence scores between breastfeeding groups for the total sample and the group of SGA children. Analyses of the total sample were weighted to account for the disproportionate sampling of SGA children. RESULTS Breastfeeding was not significantly related to intelligence scores in the total sample despite a trend for longer periods of breastfeeding to be associated with higher intelligence scores. However, in the SGA group, breastfeeding was significantly related to IQ at 3.5 y. Small for gestational age children who were breastfed for longer than 12 mo had adjusted scores 6.0 points higher than those who were not breastfed (p=0.06). CONCLUSION Breastfeeding may be particularly important for the cognitive development of preschool children born small for gestational age.

Stress and lack of social support as risk factors for small‐for‐gestational‐age birth

Aim: To determine the contributions of social support and perceived stress to the risk of small‐for‐gestational‐age birth. Methods: The investigation was a case‐control study of mothers of infants born at 37 or more completed weeks of gestation. Cases weighed less than the sex‐specific 10th percentile for gestational age at birth (small for gestational age (SGA), n= 836), and controls (appropriate for gestational age (AGA), n= 870) comprised a random selection of heavier babies. Results: In univariate analyses measures of informal social support, but not perceived stress or formal social support, were associated with SGA birth. It was found that Asian mothers are less likely to receive support from families and friends. After adjustment for ethnicity, informal social support was not associated with SGA.

Risk factors for asthma at 3.5 and 7 years of age

Background It has been suggested that factors in early life including exposure to allergens and microbes may influence the development of asthma.

Comparison of sudden infant death syndrome mortality over time and among countries

Sudden infant death syndrome (SIDS) mortality rates vary considerably in different countries. Countries such as Hong Kong have reported extremely low rates (1987: 0.3/1000 live births) (1) and others have reported very high rates (New Zealand, 1988: 4.4/1000) (2). Furthermore, in many countries SIDS rates have increased gradually over time and then in the 1990s dropped dramatically in association with a decrease in the number of infants sleeping prone (24). These differences among countries and over time are important as they provide clues as to how SIDS might be prevented, but are they real? The definition of SIDS is obviously important. In 1969 Beckwith defined SIDS as: “The sudden death of an infant or young child which is unexpected by history, and in which a full postmortem examination fails to demonstrate an adequate cause of death” (5). The major problems with this definition relate to what constitutes a full postmortem examination and what is an adequate cause of death. Probably the most frequent disagreement among pathologists relates to the importance attached to microscopic inflammatory infiltrates, especially in the lungs, but also in the myocardium and brain (6). In the past, the term “interstitial pneumonia” was used, but it is infrequently used now in most countries. The increase in SIDS mortality over time is in part explained by diagnostic transfer from respiratory deaths to SIDS. The interpretation of positive microbiological cultures is also debated (7). The pathologist has a major problem in distinguishing between SIDS and mechanical asphyxia, either accidental or non-accidental. The recently reported finding of haemosiderin in macrophages in the lungs of infants whose deaths were attributed to imposed suffocation may help in some instances (8). Various modifications to the 1969 definition have been proposed. These include limiting the diagnosis to children less than 1 y of age and including a death scene investigation (9). Others have suggested using a broad definition for legal purposes and for parents, but a strict definition for scientific purposes (10). However, the use of a very strict scientific definition may exclude important subgroups of cases. For example, infants dying while co-sleeping might be excluded because mechanical asphyxia cannot be ruled out. If all co-sleeping cases were excluded, then it might be concluded that co-sleeping decreases the risk of SIDS, whereas several studies have shown an increased risk of SIDS with co-sleeping (11, 12). In practice, not all diagnoses of SIDS are based on a postmortem examination. In many countries if a medical practitioner is prepared to issue a death certificate stating that the cause is SIDS without a postmortem examination, then that death will be certified as SIDS (ICD Code 798). The proportion of SIDS cases who have had a postmortem examination varies considerably among different countries. Some achieve almost 100% (13), whereas others report postmortem rates as low as 50% (14). In this issue, Dr Vege and Professor Rognum investigate the apparent differences in mortality from SIDS in the Nordic countriei and changes in SIDS diagnosis over time. They describe the development of a set of common diagnostic criteria for SIDS by the Nordic Pathology Group, which were adopted by all Nordic countries in 1992. They apply the Nordic criteria for classification of SIDS retrospectively to a sample of sudden unexpected infant deaths, but not necessarily SIDS, from each country. Several interesting findings are reported. Diagnoses were revised more frequently in cases from the 1970s than in more recent cases (diagnoses were revised in 56% of the Norwegian cases from the 1970-79 sample). In all countries in the period 1970-71 the revised diagnoses showed a higher proportion of SIDS than the original diagnoses. These results provide support for the contention that the increase and decline in SIDS is only partly explained by diagnostic transfer. Intraobserver reproducibility was shown to be perfect in a sample of 25 cases, whereas, despite the development and application of these criteria, the interobserver reproducibility was good, but not perfect. This study has improved the uniformity of diagnosis among different countries. By applying these criteria retrospectively greater uniformity of diagnoses over time was achieved. But how generalizable are these results? If these or other criteria were adopted by pathologists in other countries, variation in diagnosis would probably be reduced but would not be eliminated entirely (15). Assessing trends in SIDS over time by retrospective review is very expensive in pathologist time and can only be undertaken as a limited research project. Because the criteria are likely to change over time as the understanding of the pathology improves, the diagnosis achieved at the review can only be provisional, and might be revised again after a further review in, say,

Previous breastfeeding does not alter thymic size in infants dying of sudden infant death syndrome.

The relationship between thymic weights and previous feeding histories was examined in 294 infants of 37 wk gestation or more dying of sudden infant death syndrome (SIDS). One hundred and sixty‐five infants had been breastfed exclusively, 89 had been partially breastfed and 40 had never been breastfed. We found no relationship between thymic weight and type of previous feeding. The difference between these findings in SIDS and the substantially greater thymic size previously reported in 4‐mo‐old breastfed living infants deserves further study.

an adequate cause of death

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Breastfeeding and intelligence of preschool children: Breastfeeding and intelligence in preschool children

Aim: To investigate whether breastfeeding during infancy is a determinant of intelligence at 3.5 y. Methods: Five hundred and fifty European children enrolled at birth in the Auckland Birthweight Collaborative Study were assessed at 3.5 y of age. Approximately half were small for gestational age (SGA10th percentile) at birth and half were appropriate for gestational age (AGA>10th percentile). Duration of breastfeeding was recorded at maternal interview, and the intelligence of children was assessed using the Stanford Binet Intelligence Scale. Regression analysis was used to calculate estimates of difference in intelligence scores between breastfeeding groups for the total sample and the group of SGA children. Analyses of the total sample were weighted to account for the disproportionate sampling of SGA children. Results: Breastfeeding was not significantly related to intelligence scores in the total sample despite a trend for longer periods of breastfeeding to be associated with higher intelligence scores. However, in the SGA group, breastfeeding was significantly related to IQ at 3.5 y. Small for gestational age children who were breastfed for longer than 12 mo had adjusted scores 6.0 points higher than those who were not breastfed (p=0.06).