Maternal anthropometric risk factors for caesarean delivery before or after onset of labour.

OBJECTIVE: To quantify the effects of pre-pregnancy body mass and gestational weight gain, above and beyond their known effects on birthweight, on the risk of primary and repeat caesarean delivery performed before or after the onset of labour. DESIGN: Hospital-based historical cohort study. SETTING: Canadian university-affiliated hospital. POPULATION: A total of 63 390 singleton term (> or = 37 weeks gestation) infants with cephalic presentation. METHODS: We studied prospectively archived deliveries at the Royal Victoria Hospital in Montreal, Canada, from 1 January 1978 to 31 March 2001 using multiple logistic regression models to estimate relative odds of caesarean delivery. MAIN OUTCOME MEASURE: Caesarean delivery, primary or repeat and before or after the onset of labour. RESULTS: Pregravid obesity (body mass index > or = 30 kg/m2) increased the likelihood of primary caesarean delivery before (OR = 2.01, 95% CI 1.39-2.90) and after (OR = 2.12, 95% CI 1.86-2.42) the onset of labour. High net rate of gestational weight gain (> 0.50 kg/week) increased the risk but only after labour onset (OR = 1.40, 95% CI 1.23-1.60). Among women with a previous caesarean, high weight gain modestly increased risk but only before labour (OR = 1.38, 95% CI 1.04-1.83), whereas obesity increased the risk of caesarean delivery both before (OR = 1.85, 95% CI 1.44-2.37) and after (OR = 1.96, 95% CI 1.11-3.47) labour onset. Increased risks of macrosomia accounted for the association between pregravid adiposity and repeat caesarean delivery performed after but not before the onset of labour. CONCLUSIONS: Pregravid obesity increases the risk of caesarean delivery both before and after the onset of labour and both with and without a history of caesarean.

Obstetric implications of low-lying placentas diagnosed in the second trimester.

OBJECTIVES: To determine the obstetrical outcome of pregnancies initially complicated by a low-lying placenta in the second trimester. METHODS: We reviewed the obstetric outcome of all women with singleton deliveries from 1 January 1997 to 31 March 1999 and compared the 703 women with low-lying placentas (placentas in the lower uterine segment) with the 6938 women with placentas that were normally situated in the upper uterine segment at 16-22 weeks' gestation. RESULTS: Pregnancies complicated by a low-lying placenta in the second trimester were not associated with antepartum hemorrhage, preterm births, preterm prelabor rupture of membranes, pregnancy-induced hypertension, fetal growth restriction or cesarean births. However, they had a higher incidence of postpartum hemorrhage (odds ratio 1.768, 95% confidence interval 1.137, 2.748) than women with a normally situated placenta in the second trimester. CONCLUSIONS: Pregnant women with low-lying placentas in the second trimester have a higher incidence of postpartum hemorrhage and hence, it would be prudent to carefully manage the third stage of labor in these women.

Determinants of unexplained antepartum fetal deaths.

OBJECTIVE: To assess fetal, maternal, and pregnancy-related determinants of unexplained antepartum fetal death. METHODS: We conducted a hospital-based cohort study of 84,294 births weighing 500 g or more from 1961-1974 and 1978-1996. Unexplained fetal deaths were defined as fetal deaths occurring before labor without evidence of significant fetal, maternal, or placental pathology. RESULTS: One hundred ninety-six unexplained antepartum fetal deaths accounted for 27.2% of 721 total fetal deaths. Two thirds of the unexplained fetal deaths occurred after 35 weeks' gestation. The following factors were independently associated with unexplained fetal death: maternal prepregnancy weight greater than 68 kg (adjusted odds ratio [OR] 2.9; 95% confidence interval [CI] 1.85, 4.68), birth weight ratio (defined as ratio of birth weight to mean weight for gestational age) between 0.75 and 0.85 (OR 2.77; 95% CI 1.48, 5.18) or over 1.15 (OR 2.36; 95% CI 1.26, 4.44), fewer than four antenatal visits in women whose fetuses died at 37 weeks or later (OR 2.21; 95% CI 1.08, 4.52), primiparity (OR 1.74; 95% CI 1.26, 2.40), parity of three or more (OR 2.01; 95% CI 1.26, 3.20), low socioeconomic status (OR 1.59; 95% CI 1.14, 2.22), cord loops (OR 1.75; 95% CI 1.04, 2.97) and, for the 1978-1996 period only, maternal age 40 years or more (OR 3.69; 95% CI 1.28, 10.58). Trimester of first antenatal visit, low maternal weight, postdate pregnancy, fetal-to-placental weight ratio, fetal sex, previous fetal death, previous abortion, cigarette smoking, and alcohol use were not significantly associated with unexplained fetal death. CONCLUSION: In this study, we identified several factors associated with an increased risk of unexplained fetal death.

Knobloch syndrome involving midline scalp defect of the frontal region.

We report on a 4-year-old boy with Knobloch syndrome. He has vitreoretinal degeneration, high myopia, cataract, telecanthus, hypertelorism, and a high-arched palate. He also has a defect of the anterior midline scalp with involvement of the frontal bone as documented by a computed tomography (CT) scan. The brain was normal on CT scan and magnetic resonance imaging. We present a review of the 23 published cases with this syndrome. Our patient illustrates the importance of investigating for underlying ocular and central nervous system pathology whenever midline scalp defects are present.

Are all growth-restricted newborns created equal(ly)?

BACKGROUND: Previous etiologic studies have defined intrauterine growth restriction (IUGR) based on a single cutoff. OBJECTIVE: To assess the relative importance of known etiologic determinants for different degrees (mild versus severe) and timing (preterm versus term) of fetal growth restriction. DESIGN: Hospital-based cohort study. SETTING: Tertiary-care university hospital. PARTICIPANTS: Sixty-five thousand two hundred eighty inborn singleton infants without major congenital anomalies delivered between January 1, 1978 and March 31, 1996. MEASUREMENTS: Comparison of adjusted odds ratios (ORs) and 95% confidence intervals for mild IUGR (defined as birth weight 75% to <85% of the mean for gestational age, the latter cutoff equivalent to the 9.9th percentile for this cohort) and severe IUGR (<75% of mean, or 2.3rd percentile), after controlling for maternal age, education, marital status, and other potential determinants by means of multiple logistic regression. RESULTS: Maternal prepregnancy overweight (body mass index [BMI] >26.0-29.0 kg/m2) and obesity (BMI >29.0 kg/m2) had stronger protective effects against mild IUGR than against severe IUGR, but most of the determinants showed the opposite pattern. This was especially true for pathologic determinants; ORs (and 95% confidence intervals) for severe versus mild IUGR were 18.5 (14.5-23.8) vs 4.6 (3.6-5.8) for severe pregnancy-induced hypertension (PIH), 3.5 (2.2-5.5) vs 2.3 (1. 5-3.4) for prepregnancy hypertension, and 3.4 (2.9-3.9) vs 2.2 (2. 0-2.4) for smoking >/=11 cigarettes/day. Primiparity, short stature, prepregnancy BMI, maternal weight gain, and cigarette smoking had significantly larger effects on term IUGR, whereas the effect of severe PIH was more than twice as large for preterm IUGR (OR = 9.7 [7.3-13.0]) as for term IUGR (OR = 4.0 [3.0-5.3]). CONCLUSION: Pathologic determinants of IUGR such as prepregnancy and PIH and cigarette smoking predispose to more severe fetal growth retardation, and PIH in particular seems to do so before 37 weeks. Growth-restricted newborns are not, therefore, all created equal(ly).

Secular trends in preterm birth: a hospital-based cohort study.

CONTEXT: Canada and the United States have reported a recent increase in the incidence of preterm birth, but the reasons for this increase are unknown. OBJECTIVE: To assess secular trends in preterm birth and its potential determinants. DESIGN: Hospital-based cohort study. SETTING: Canadian tertiary care university teaching hospital, 1978-1996. PARTICIPANTS: A total of 65574 nonreferred live births and stillbirths. MAIN OUTCOME MEASURES: Changes in occurrence of preterm birth, before and after adjustment for changes in method of gestational age assessment, obstetric intervention, registration of births weighing less than 500 g, and sociodemographic, behavioral, and clinical determinants. RESULTS: A crude secular increase in preterm births was seen for births less than 37, 34, and 32 completed weeks using 3 alternative gestational age estimation methods. Based on an algorithm incorporating both menstrual and early ultrasound gestational age estimates, rates increased from 6.6% to 9.8% for births at less than 37 weeks' gestation, 1.7% to 2.3% at less than 34 weeks, and 1.0% to 1.2% at less than 32 weeks. Exclusion of births weighing less than 500 g and those with induction or preterm cesarean delivery without labor before each of the corresponding gestational age cutoffs eliminated the secular trends for births before 34 and 32 weeks and attenuated the trend for births before 37 weeks. Nearly half of the remaining trend for births before 37 weeks was accounted for by the increasing use of early ultrasound dating. The residual trend was eliminated after controlling for secular increases in unmarried status and the proportion of women aged 35 years or older. These factors, combined with a decrease in alcohol consumption and increases in histological chorioamnionitis and cocaine use, appear to have counteracted a reduction in preterm birth since the mid-1980s that otherwise would have been observed. CONCLUSIONS: This hospital's increase in preterm births since 1978 parallels increases reported in population-based national studies from the United States and Canada. This trend appears largely attributable to the increasing use of early ultrasound dating, preterm induction and preterm cesarean delivery without labor, and changes in sociodemographic and behavioral factors.

Factors associated with growth of extremely premature infants during initial hospitalization.

OBJECTIVE: To quantify the factors associated with growth of very small premature infants during initial hospitalization. POPULATION: Study patients were 109 infants who were appropriate for gestational age, weighed <1000 g at birth, and were fed intravenous hyperalimentation then calcium-supplemented 81-kcal preterm formula according to a protocol. ANALYSIS: Multiple regression analysis was performed for periods of 0 to 56, 0 to 14, and 15 to 56 days of age. Growth was determined as change in weight during the period. Variables assessed in the initial model were caloric intake, protein intake, respiratory support duration, patent ductus arteriosus, dexamethasone use, infection, birth weight ratio (weight divided by expected intrauterine weight for gestation), gestational age, sex, calendar time from study start, maternal betamethasone administration, and necrotizing enterocolitis. For the 0 to 14-day period, maximum oxygen requirement for respiratory distress syndrome replaced respiratory support duration, and 5-minute Apgar score was added, whereas dexamethasone and necrotizing enterocolitis were deleted. RESULTS: Mean change in weight was 785 g for 0 to 56 days, -16 g for 0 to 14 days, and 770 g for 15 to 56 days. Mean weight was 94% (13 SD) of mean intrauterine at birth, 73% (10 SD) at 14 days, and 73% (12 SD) at 56 days. Regression models explained 85%, 43%, and 80%, respectively, of variation in growth. Of the initial variables assessed, the following were the independent prognostic determinants of growth. There was a positive association with caloric intake at 0 to 56 days and 15 to 56 days, and with protein intake at 0 to 14 days. Negative associations were found for birth weight ratio and gestational age at 0 to 56 and 0 to 14 days. Respiratory support duration was negatively associated at 15 to 56 days, and dexamethasone was negatively associated at 0 to 56 and 15 to 56 days. Formulas to predict growth were established from the final regression models. CONCLUSION: The growth failure in appropriate-for-gestational-age, <1000-g birth weight infants can be related in part to dexamethasone use and respiratory support duration. Increasing caloric intake and early protein intake improves growth. However, for the majority of these patients, early losses are not corrected completely by 56 days using currently recommended intakes.

Growth of very premature infants fed intravenous hyperalimentation and calcium-supplemented formula.

OBJECTIVE: To describe growth during initial hospitalization for very small premature infants fed intravenous hyperalimentation, then calcium supplemented 1460 mg/L (36.5 mmol/L) 81 kcal preterm formula. POPULATION: A total of 109 survivors whose <1000 g birth weight was appropriate for gestational age. Mean gestational age was 25.8 weeks. RESULTS: Graphs were constructed for weight, length, and head circumference by week of age. Mean and +/- 2 SD lines were depicted, with mean intrauterine growth lines for comparison. Separate graphs showed mean weight, length, and head circumference growth by 100 g birth weight cohorts. Mean Z scores based on normal intrauterine growth curves were calculated. Weight Z scores were -.35 at birth, -1.79 at 14 days, and -1.87 at 56 days. Length Z scores were -.32 at birth, -1.29 at 14 days, and -2.24 at 56 days. Head circumference Z scores were 0.01 at birth, -1.26 at 14 days, and -1.06 at 56 days. (Z score = [measured parameter - intrauterine mean for gestation]/intrauterine SD for gestation). Repeated-measures multivariate ANOVAs showed the following significant Z score changes. There were decreases in Z scores for weight, length, and head circumference between birth and 14 days and an additional decrease for length between 14 and 56 days. Head circumference Z scores increased from day 14 to day 56, but remained smaller at day 56 than at day 0. Initially, head circumference Z scores were better than weight or length (possibly because of late head measurement timing). At day 14, the Z scores for weight were lower than those for length and head circumference. At day 56, the head circumference Z scores were higher than those for length or weight. CONCLUSION: Compared with intrauterine standards, weight, length, and head circumference were all worse at day 56 than at birth, although there was relative head-sparing and weight growth paralleled intrauterine growth after 14 days. Length worsened from day 14 to day 56 in spite of the use of calcium and phosphorus-enriched formula.

Etiologic determinants of abruptio placentae.

OBJECTIVE: To quantify the roles of suspected sociodemographic, anthropometric, behavioral, and pathologic determinants in the etiology of abruptio placentae. METHODS: We performed a hospital-based cohort study of 36,875 nonreferred births between January 1978 and March 1989. Gestational age was based on menstrual dates confirmed (within 7 days) by early ultrasound. RESULTS: Parity, maternal education, pre-pregnancy weight, and the rate of net gestational weight gain did not have significant independent associations with abruption. Significant determinants included the following: severe small for gestational-age (SGA) birth (odds ratio [OR] 3.99; 95% confidence interval [CI] 2.75, 5.77), chorioamnionitis (OR 2.50; 95% CI 1.58, 3.98), prolonged rupture of membranes (OR 2.38; 95% CI 1.55, 3.65), preeclampsia (OR 2.05; 95% CI 1.39, 3.04), pregnancy-induced hypertension without albuminuria (OR 1.57; 95% CI 1.00, 2.46), pre-pregnancy hypertension (OR 1.77; 95% CI 1.05, 2.99), maternal age at least 35 years (OR 1.50; 95% CI 1.14, 2.01), unmarried status (OR 1.50; 95% CI 1.13, 1.98), cigarette smoking (OR 1.40; 95% CI 1.00, 1.97 for ten to 19 cigarettes per day and OR 1.13; 95% CI 0.81, 1.59 for at least 20 cigarettes per day), and male fetal gender (OR 1.38; 95% CI 1.12, 1.70). Removal of SGA from the regression model resulted in little change in the magnitude of the other associations. CONCLUSIONS: Severe fetal growth restriction, prolonged rupture of membranes, chorioamnionitis, hypertension (before pregnancy and pregnancy-induced), cigarette smoking, advanced maternal age, unmarried status, and male fetal gender are significant etiologic determinants of placental abruption. Non-SGA determinants appear to operate largely independently of their effects on fetal growth.

Causes of fetal death in women of advanced maternal age.

OBJECTIVE: To examine which causes of fetal death occur more often in older women and to determine whether these causes have changed significantly since the 1960 s and early 1970 s. METHODS: Data from the McGill Obstetrical Neonatal Database were used to calculate rates of specific causes of fetal death in women younger than 35 and in women 35 years or older. Among the 101,640 births between 1961 and 1995, there were 715 stillbirths and 822 neonatal deaths. The autopsy rate was 97% and categorization of the causes of fetal death remained consistent over this 34-year period. The rates of specific causes of fetal death per 10,000 total births were determined for an earlier period (1961-1974) and a later period (1978-1995). RESULTS: Compared with the 1961-1974 period, there was a 60% reduction in the rates of both fetal and neonatal deaths during 1978-1995 (P < .001). During 1961-1974, women 35 years or older were more likely than their younger counter-parts to have fetal death due to lethal congenital anomalies (odds ratio [OR] 3.2; 95% confidence interval [CI] 1.5, 6.5); this was no longer true in the 1978-1995 period. From 1978 to 1995, older women were at a statistically significant increased risk for "unexplained" fetal death (OR 2.2; 95% CI 1.3, 3.8); women 35 years of age or older had approximately one in 440 births end in unexplained fetal death, compared to one in 1000 births for women younger than 35. CONCLUSIONS: Advanced maternal age is no longer associated with an increased risk for fetal death due to congenital anomalies. However, older women have a significantly higher risk for unexplained fetal death. The identification of those maternal and fetal characteristics that contribute to unexplained fetal death and its prevention remain important challenges for contemporary obstetric practice.

Recurrent respiratory distress syndrome in successive preterm pregnancies.

BACKGROUND: Earlier studies suggesting an increased recurrence risk of respiratory distress syndrome (RDS) among the subsequent infants of women with a previously affected infant were based on low birth weight inclusion criteria that did not differentiate between preterm and growth-retarded infants. METHODS: We therefore carried out two cohort studies of women who delivered two singleton preterm (gestational age < 37 completed weeks) infants: 1978 to 1989 at the Royal Victoria Hospital (RVH) in Montreal and 1959 to 1966 in the United States Collaborative Perinatal Project (CPP). We compared the relative risk (RR) of the development of RDS in the second infant according to the RDS status of the first. The diagnosis of RDS was based on respiratory distress of more than 24 hours' duration and a reticulogranular pattern on a chest radiograph. RESULTS: The RVH study sample comprised 284 infants born to 142 women, and the CPP sample 642 infants born to 321 mothers. In the RVH cohort the crude RR of RDS in the second sibling was 3.3 (95% confidence interval = 1.0 to 15.1) in women whose first preterm infant had RDS versus those whose first preterm infant did not have RDS. In the CPP cohort the corresponding RR was 2.5 (95% confidence interval = 0.8 to 7.9). These elevated risks were not altered substantially when multiple logistic regression was used to control for potentially confounding factors known to influence the risk of RDS (gestational age, sex, route of delivery, antenatal corticosteroids, and respiratory depression of birth). CONCLUSIONS: We conclude that preterm infants born to women with a previous preterm infant affected by RDS are at an increased risk of RDS, which suggests an important genetic (or other familial) tendency in its origin.

Increased maternal age and the risk of fetal death.

BACKGROUND: Although the fetal death rate has declined over the past 30 years among women of all ages, it is unknown whether particular characteristics of the mother, such as age, still affect the risk of fetal death. We undertook a study to determine whether older age, having a first child (nulliparity), or other characteristics of the mother are risk factors for fetal death. METHODS: We used data from the McGill Obstetrical Neonatal Database to evaluate risk factors for fetal death among all deliveries at the Royal Victoria Hospital in Montreal (n = 94,346) from 1961 through 1993. Data were available for two time periods (1961 through 1974 and 1978 through 1993); data for 1975 through 1977 have not been entered into the data base and were therefore not included. Using logistic regression, we estimated the effect of specific maternal characteristics and complications of pregnancy on the risk of fetal death. RESULTS: The fetal death rate decreased significantly from 11.5 per 1000 total births (including live births and stillbirths) in the 1960s to 3.2 per 1000 in 1990 through 1993 (P < 0.001). Between these periods, the average maternal age at delivery increased from 27 to 30 years (P < 0.001), and the frequency of the diagnosis of diabetes and hypertension during pregnancy increased fivefold (P < 0.001). Nevertheless, after we controlled for these and other maternal characteristics, women 35 years of age or older continued to have a significantly higher rate of fetal death than their younger counterparts (odds ratio for women 35 to 39 years of age as compared with women < 30 years of age, 1.9; 95 percent confidence interval, 1.3 to 2.7; for those 40 or older, 2.4; 95 percent confidence interval, 1.3 to 4.5). CONCLUSIONS: Changes in maternal health and obstetrical practice have resulted in a 70 percent decline in the rate of fetal death among pregnant women of all ages since the 1960s. Advancing maternal age, however, continues to be a risk factor for fetal death.

Comparison of birth weight distributions between Chinese and Caucasian infants.

To assess the reasons for the Chinese-Caucasian differences in birth weight distributions, a cohort study was carried out involving 18,665 Caucasian and 1,597 immigrant Chinese infants born at Montreal's Royal Victoria Hospital from January 1978 to March 1990 and 1,862 native Chinese infants born at Hefei Maternal and Infant Hospital in Hefei, People's Republic of China, from September 1990 to August 1991. Mean (standard deviation) birth weights in grams were 3,369 (567), 3,195 (493), and 3,171 (428) (p < 0.01 for differences in mean and variance), and mean (standard deviation) fetal growth ratios (ratio of observed birth weight to average birth weight at the same gestational age) were 0.994 (0.124), 0.963 (0.114), and 0.935 (0.112) (p < 0.01 for differences in mean and variance), respectively, in the Caucasian, immigrant Chinese, and native Chinese groups. No important or consistent Chinese-Caucasian differences in gestational age were found. When mothers with extreme values for demographic, anthropometric, nutritional, and lifestyle determinants of fetal growth were excluded, the mean fetal growth ratio in Caucasian infants remained significantly higher (p < 0.01), but the standard deviations became more similar (p > 0.05): Mean (standard deviation) fetal growth ratios were 1.001 (0.111), 0.966 (0.108), and 0.946 (0.114), respectively. The race-specific rate of growth differed according to period of gestation, with Chinese infants showing more rapid fetal growth early in the third trimester but slower growth near and after term. The authors conclude that the lower mean birth weight in Chinese infants is due to differences in fetal growth (rather than gestational duration) and by their inherently slower growth at or after term. The tight distribution of birth weight among the Chinese is caused partly by their reduced exposure to extremes of maternal determinants of fetal growth (mediated largely by environmental mechanisms) and partly by their inherently different growth pattern, with faster growth at earlier gestations but slower growth at later gestations.

Terminal digit preference, random error, and bias in routine clinical measurement of blood pressure.

We examined the presence, magnitude, and consequences of systematic and random errors caused by terminal digit preference in the measurement of highest systolic blood pressure during prenatal visits in 28,841 non-referred pregnant women who delivered between 1 January 1982 and 31 March 1990. In the overall distribution of terminal digit readings, 78% were read to 0, 15% to even digits other than 0, 5% to 5, and only 2% to odd digits other than 5. This preference for 0's was consistent across the entire distribution of blood pressure and for a variety of maternal characteristics. The relative frequency of the cutoff value of 140 mmHg (i.e. the percentage of readings on 140 mmHg) within the range containing the value (i.e. 138-142 mmHg) was similar to the relative frequency of other multiples of 0. This was true whether the comparison was made in the overall study sample, or in a pre-selected low-risk subgroup or high-risk subgroup, indicating no systematic bias. On the other hand, a strong tendency to read blood pressure values to the nearest 0 had a marked effect on the classification of hypertension. Changing the definition of hypertension from > or = 140 mmHg to > 140 mmHg produced a reduction in prevalence of hypertension from 25.9 to 13.3% in the overall study sample, from 15.4 to 6.3% in the low-risk subgroup, and from 43.3 to 25.3% in the high-risk subgroup. Epidemiologic studies that compare prevalences of hypertension in different populations based on routine clinical measurement of blood pressure and a single cutoff point should assess the consequences of terminal digit preference in defining hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal nutrition and spontaneous preterm birth.

Previous studies suggesting that maternal undernutrition increases the risk of preterm birth have suffered from several methodological shortcomings, including use of total gestational weight gain rather than net rate of gain in maternal tissue, inclusion of induced preterm deliveries, and error-prone gestational age measurements based solely on menstrual dates. The authors have attempted to overcome these shortcomings by investigating the potential etiologic roles of prepregnancy body mass index, net rate of maternal weight gain, height, and a number of other potential biological and sociodemographic determinants of spontaneous (i.e., noninduced) preterm birth in a cohort of 13,102 women with early ultrasound-confirmed gestational age who delivered at the Royal Victoria Hospital in Montreal, Quebec, Canada, between January 1, 1980 and March 31, 1989. Total weight gain, but not body mass index, was highly significantly associated with spontaneous preterm birth, averaging 14.6, 12.5, 9.9, and 9.1 kg, in women delivering at 37 or more, less than 37, less than 34, and less than 32 completed weeks, respectively. Although the relation persisted when weight gain was expressed as an overall rate, it disappeared when the analysis was based on net rate; mean net rates of gain were 0.28, 0.29, 0.27, and 0.27 kg/week, respectively. On the basis of multiple logistic regression analyses, significant determinants of birth at less than 37 weeks included maternal short stature; noncompletion of high school; unmarried status; smoking; diabetes; urinary tract infection within 2 weeks of delivery; prepregnancy hypertension; severe pregnancy-induced hypertension; and previous history of preterm delivery, low birth weight, or neonatal death. Most of these factors retained their significance for birth at less than 34 and less than 32 weeks. In fact, the effect of low maternal education was even stronger at these more severe "levels" of preterm birth. The authors conclude that prepregnancy weight-for-height and gestational weight gain are not important determinants of spontaneous preterm birth and that some previous studies have mistaken an effect of shortened gestation for its cause. Other biologic and social determinants, however, indicate priorities for future research and intervention.

The changing pattern of fetal death, 1961-1988.

The aim of this study was to assess any changes in cause-specific fetal death rates in the nonreferred population of a tertiary care unit. The fetal death rate (per 1000 births) among 88,651 births diminished from 11.5 in the 1960s to 5.1 in the 1980s. Fetal death due to intrapartum asphyxia and Rh isoimmunization has almost disappeared. Toxemia and diabetes continue to make similar and small contributions to fetal death rates. There has been a significant decline in unexplained antepartum fetal deaths and in those caused by fetal growth retardation, but no significant change in the death rate due to intrauterine infection or abruptio placentae. During the 1960s, the risk of fetal death was increased in women with hypertension, diabetes, or a history of stillbirth; during the 1980s, only women with a history of insulin-dependent diabetes were at risk. Improved application of current knowledge may help decrease the fetal death rate caused by fetal growth retardation. Reduction in deaths due to abruptio placentae, intrauterine infections, or lethal malformations, as well as unexplained antepartum deaths, appears to depend on better understanding of the etiology of these disorders.

Very low birth weight: a problematic cohort for epidemiologic studies of very small or immature neonates.

Despite widespread acceptance of the concept of very low birth weight (VLBW), i.e., birth weight of less than or equal to 1,500 g, VLBW infants represent an extremely heterogeneous group of newborns, including those with very immature gestational age and those who are more mature but extremely growth retarded. To demonstrate how use of the VLBW rubric can lead to confounding bias that is not only large in magnitude but impossible to control satisfactorily, the authors divided 640 consecutive live neonates born in the Royal Victoria Hospital, Montreal, Canada, from 1978 to 1987 into two overlapping groups: a VLBW cohort (birth weight, 500-1500 g; n = 573) and a gestational age cohort (gestational age, 23-30 completed weeks; n = 466). Variation in growth status by gestational age was much more uniform in the 23- to 30-week cohort. Thus, although mean birth weight was similar in the 500- to 1,500-g and 23- to 30-week cohorts (1,055 vs. 1,064 g), the 500- to 1,500-g cohort was more mature (mean gestational age, 28.8 vs. 27.8 weeks; upper range, 39.7 vs. 30.9 weeks) and had twice the rate of intrauterine growth retardation (25.7 vs. 11.5%). These differences in maturity and growth resulted in a misleading protective effect of intrauterine growth retardation against in-hospital death in the 500- to 1,500-g cohort (crude odds ratio = 0.55 (95% confidence interval 0.36-0.83] and a greater discrepancy in maturity between cesarean- and vaginally delivered infants (3.1 vs. 1.5 weeks) in the 500- to 1,500-g vs. 23- to 30-week cohorts. These differences arise from inextricable confounding of growth status and maturity in the 500- to 1,500-g cohort, the most mature infants also being the most growth retarded. The removal of well-grown infants with birth weights of greater than 1,500 g from the VLBW cohort leads to a progressively distorted spectrum of growth with advancing gestational age and an artifactual blunting of the beneficial effects of increasing maturity. The authors suggest that whenever fetal growth is an important exposure, outcome, or confounding variable, epidemiologic studies of extremely small or immature newborns should be based on gestational age rather than the VLBW criterion.

Postterm infants: too big or too small?

Concern over the postterm pregnancy has shifted from that of the difficult delivery of an excessively large fetus to the current concern with death in utero of an undernourished, small-for-date fetus. Studies of postterm pregnancy before the availability of ultrasonography may have included a large proportion of erroneous menstrual dates. The present study of 7000 infants was undertaken to reassess fetal growth in postterm pregnancies in which the expected date of confinement from last normal menstrual period dating was confirmed (+/- 7 days) by early ultrasonography. Results show a gradual shift toward higher birth weight and greater crown-heel length and head circumference between 273 and 300 days of gestational age. No evidence of postterm weight loss or lower weight for length could be demonstrated. Concern in postterm pregnancy should be for fetal macrosomia, not for intrauterine growth retardation.

Impact of intrauterine growth retardation and body proportionality on fetal and neonatal outcome.

Previous prognostic studies of infants with intrauterine growth retardation (IUGR) have not adequately considered the heterogeneity of IUGR in terms of cause, severity, and body proportionality and have been prone to misclassification of IUGR because of errors in estimation of gestational age. Based on a cohort of 8719 infants with early-ultrasound-validated gestational ages and indexes of body proportionality standardized for birth weight, the consequences of severity and cause-specific IUGR and proportionality for fetal and neonatal morbidity and mortality were assessed. With progressive severity of IUGR, there were significant (all P less than .001) linear trends for increasing risks of stillbirth, fetal distress (abnormal electronic fetal heart tracings)O during parturition, neonatal hypoglycemia (minimum plasma glucose less than 40 mg/dL), hypocalcemia (minimum Ca less than 7 mg/dL), polycythemia (maximum capillary hemoglobin greater than or equal to 21 g/dL), severe depression at birth (manual ventilation greater than 3 minutes), 1-minute and 5-minute Apgar scores less than or equal to 6, 1-minute Apgar score less than or equal to 3, and in-hospital death. These trends persisted for the more common outcomes even after restriction to term (37 to 42 weeks) births. There was no convincing evidence that outcome among infants with a given degree of growth retardation varied as a function of cause of that growth retardation. Among infants with IUGR, increased length-for-weight had significant crude associations with hypoglycemia and polycythemia, but these associations disappeared after adjustment for severity of growth retardation and gestational age.(ABSTRACT TRUNCATED AT 250 WORDS)