Measurement error in clinical perinatal data

Measurement and Standardization Protocols for Anthropometry Used in the Construction of a New International Growth Reference

The objective of the Motor Development Study was to describe the acquisition of selected gross motor milestones among affluent children growing up in different cultural settings. This study was conducted in Ghana, India, Norway, Oman, and the United States as part of the longitudinal component of the World Health Organization (WHO) Multicentre Growth Reference Study (MGRS). Infants were followed from the age of four months until they could walk independently. Six milestones that are fundamental to acquiring self-sufficient erect locomotion and are simple to evaluate were assessed: sitting without support, hands-and-knees crawling, standing with assistance, walking with assistance, standing alone, and walking alone. The information was collected by both the children's caregivers and trained MGRS fieldworkers. The caregivers assessed and recorded the dates when the milestones were achieved for the first time according to established criteria. Using standardized procedures, the fieldworkers independently assessed the motor performance of the children and checked parental recording at home visits. To ensure standardized data collection, the sites conducted regular standardization sessions. Data collection and data quality control took place simultaneously. Data verification and cleaning were performed until all queries had been satisfactorily resolved.

Maternal height and newborn size relative to risk of intrapartum caesarean delivery and perinatal distress

OBJECTIVE

To estimate the changes, in risk of intrapartum caesalrean delivery and perinatal distress that may be introduced through increased birth size, resulting from interventions such as improving nutrition of the mother; and to characterise delivery risk relative to maternal stature by birth size.

DESIGN

Model these risks using data from the Guatemalan Perinatal Study.

SETTING

The antenatal clinic of the Gynaecology and Obstetrics Hospital of the Guatemalan Social Security Institute in Guatemala City serving predominantly working class women.

POPULATION

Women who had their first prenatal visit between April 1984 and January 1986.

METHODS

Multivariate logistic regression models were developed to estimate incidence of intrapartum caesarean delivery and perinatal distress and used to calculate changes in risk associated with changes in size.

MAIN OUTCOME MEASURES

Incidences of intrapartum caesarean delivery and perinatal distress.

RESULTS

A woman of 146cm height (-1 SD) relative to another of 160 cm (+1 SD) has a 2.5 times higher risk of intrapartum caesarean delivery. An increase in newborn head circumference and weight (from -1 SD to +1 SD) are each independently associated with an increase in risk of intrapartum caesarean delivery (2.0 times and 1.5 times. respectively). An increase in birthweight from 2,450 g to 2,550 g is associated with a decrease in risk of perinatal distress of 34/1,000 cases and an increase in risk of intrapartum caesarean delivery of 8/1,000 cases.

CONCLUSIONS

Increases in fetal growth comparable to those attributable to improved nutrition during pregnancy are associated with a larger decrease in risk of perinatal distress relative to the increase in risk of intrapartum caesarean delivery for the mother. Greater maternal stature is associated with lower risk of intrapartum caesarean delivery.

Maternal zinc supplementation does not affect size at birth or pregnancy duration in Peru

To estimate the effect of maternal zinc deficiency on pregnancy outcomes, we conducted a zinc supplementation trial in an urban shantytown in Lima, Peru, a population with habitual low zinc intakes. Beginning at 10-24 wk gestation, 1295 mothers were randomly assigned to receive prenatal supplements containing 60 mg iron and 250 (g folate, with or without 15 mg zinc. Women were followed up monthly during pregnancy. At birth, newborn weight was recorded, and crownheel length, head circumference and other circumferences and skinfold thicknesses were assessed on d 1. At delivery, 1016 remained in the study; duration of pregnancy was known for all women, and birth weight information was available for 957 newborns. No differences were noted in duration of pregnancy (39.4 +/- 2.2 vs. 39. 5 +/- 2.0 wk) or birth weight (3267 +/- 461 vs. 3300 +/- 498 g) by prenatal supplement type (iron + folate + zinc vs. iron + folate; P > 0.05), and there were no differences in the rates of preterm (<37 wk) or post-term (>42 wk) delivery, low birth weight (<2500 g) or high birth weight (>4000 g). Finally, there were no differences by prenatal supplement type in newborn head circumference, crownheel length, chest circumference, mid-upper arm circumference, calf circumference or skinfold thickness at any of three sites. Adjustment for covariates and confounding factors did not alter these results. Adding zinc to prenatal iron and folate tablets did not affect duration of pregnancy or size at birth in this population.

Effect of fat and fat-free mass deposition during pregnancy on birth weight

OBJECTIVES

The purposes of our study were to describe the patterns and location of fat and fat-free mass deposition during pregnancy and to evaluate their effects on fetal growth.

STUDY DESIGN

Our study is a prospective follow-up of 105 healthy pregnant women who were delivered of term infants. Body composition was evaluated eight times during gestation with anthropometric measures and bioimpedance techniques. Body fat and fat-free mass were calculated with equations specifically developed for this population.

RESULTS

Total weight gain was 10.0 +/- 3.5 kg; net weight gain was 3.7 +/- 0.31 kg; birth weight was 3211 +/- 467 gm (values are mean +/- SEM). In these women fat was deposited mostly in the thigh and subscapular region for a total of 6.23 +/- 0.19 kg at term. The period of pregnancy of the largest maternal fat deposition per week is between the twentieth and thirtieth weeks. After adjusting by prepregnancy weight, birth weight is associated with maternal changes in thigh skin folds and fat gain before the thirtieth week of gestation. Infants born to mothers with low fat gain before the thirtieth week were 204 gm lighter than infants born to mothers with fat gain > or = 25th percentile of this population.

CONCLUSION

Maternal nutritional status at the beginning of gestation and the rate of fat gain early in pregnancy are the two nutritional indicators most strongly associated with fetal growth in this population.

Prediction of fetal growth deviations by use of symphysis-fundus height measurements

The development of various symphysis fundus (SF) growth charts and the use of SF height measurements in the diagnosis of small-for-gestational-age (SGA) births and the prediction of newborn complications are reviewed. Measurement precision and accuracy are also discussed. It is concluded that further research of this simple, low cost, harmless, and widespread technology to detect fetal growth disturbances in routine prenatal care is warranted.

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 differential neonatal morbidity of the intrauterine growth retardation syndrome

This is a prospective study of differential morbidity among subgroups of intrauterine growth retardation. Cases of intrauterine growth retardation (N = 3450) (greater than or equal to 37 weeks, less than 10th percentile birth weight for gestational age) were classified by their ponderal index (weight/length3) in four subgroups using the 10th, 25th, and 90th percentiles of the Lubchenco's ponderal index-gestational age distribution. There were 432 cases (12.5%) with low ponderal index or disproportionate intrauterine growth retardation, 936 (27.1%) with intermediate ponderal index, 2030 (58.8%) with adequate ponderal index or proportionate intrauterine growth retardation, and 52 (1.5%) with high ponderal index. The low ponderal index group or disproportionate intrauterine growth retardation group had a statistically significant higher risk (between 1.6 and 12.5 times) for low 1- and 5-minute Apgar scores, aspiration syndrome, hypoglycemia, and perinatal asphyxia than the adequate ponderal index group. The low ponderal index group also had an increased risk (relative risk = 2.0 [95% confidence interval, 1.0 to 3.8]) for hospital stay of more than 1 week. These differences persist after a stratified analysis by birth weight and in a multiple logistic regression analysis. Similarly, higher neonatal morbidity is observed among infants with normal birth weights but with low ponderal index. These data provide further evidence of the heterogeneity of the intrauterine growth retardation syndrome and of the independent effect of body disproportion on neonatal morbidity, even among infants with normal birth weights. Because there are significant clinical implications attributed to the low ponderal index group, this subgroup should be identified as early as possible.

Variability of symphysis-fundus height measurements: an experimental study among general practitioners

With the aim of evaluating the impact of supervised training during a postgraduate course in obstetrics and gynaecology, the variability of symphysis-fundus (SF) height measurements was studied by a group of general practitioners (GPs), all of whom provided primary antenatal care. A nested analysis of variance was used. The SF height measurements of the group differed significantly from those of a senior obstetrician and the course training had no impact on the variability. Similar studies should evaluate measurement variability in the light of pregnancy outcome.

The measuring of blood pressure during pregnancy

This is an evaluation of the methodology of blood pressure measurement in a high-risk obstetric clinic. Blood pressure values were obtained from 149 patients by the clinic staff and the research project coordinator. The project coordinator using the random-zero sphygmomanometer measured lower systolic and higher diastolic values. The diastolic and systolic values increased after 30 weeks of pregnancy up to term. Agreement among observers is low for diastolic blood pressure. The clinic staff measured about 50% of the values with a zero terminal digit as compared with only 14% by the project coordinator. The fourth Korotkoff sound can be recorded in 83% of the patients. The mean diastolic blood pressures obtained with the fourth sound are significantly higher than when the fifth sound is used. Recommendations are offered for blood pressure measuring during pregnancy, and it is strongly suggested that the same methodologic rigor be used as in any other medical procedure.