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.

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.

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)

Determinants of fetal growth and body proportionality.

Previous studies of fetal growth and body proportionality have been based on error-prone gestational age estimates and on inappropriate comparisons of infants with dissimilar birth weights. Based on a cohort of 8719 infants with validated (by early ultrasonography) gestational ages and indexes of body proportionality standardized for birth weight, potential maternal and fetal determinants of fetal growth and proportionality were assessed. Maternal history of previous low birth weight infants, pregnancy-related hypertension (particularly if severe), diabetes, prepregnancy weight, net gestational weight gain, cigarette smoking, height, parity, and fetal sex were all significantly associated with fetal growth in the expected directions. Consistent with previous reports, maternal age, marital status, and onset or total amount of prenatal care had no significant independent effects. Fetal growth ratio (relative weight for gestational age), pregnancy-related hypertension, fetal sex, and maternal height were the only significant determinants of proportionality. Infants who were growth-retarded, those with taller mothers, those whose mothers had severe pregnancy-related hypertension, and males tended to be longer and thinner and had larger heads for their weight, although these variables explained only a small fraction of the variance in the proportionality measures. Among infants with intrauterine growth retardation, gestational age was not independently associated with proportionality (in particular, late term and post-term infants did not tend to be more disproportional), a finding that does not support the hypothesis that earlier onset of growth retardation leads to more proportional growth retardation. The results raise serious questions about previous studies of proportionality, particularly those suggesting a nutritional etiology for proportional intrauterine growth retardation.(ABSTRACT TRUNCATED AT 250 WORDS)

Body proportionality and head and length 'sparing' in growth-retarded neonates: a critical reappraisal.

Despite the popular current distinction between "proportional" and "disproportional" intrauterine growth retardation, it has never been shown that variation in body proportions is greater among growth-retarded than nongrowth-retarded infants of the same birth weight, nor that proportionality is distributed bimodally among growth-retarded infants. Based on a cohort of 8719 neonates born between 1980 and 1986 of mothers with concordant (+/- 7 days) menstrual dating and early ultrasound estimates of gestational age, we used a continuous measure of birth weight for gestational age to define four study groups: nongrowth retarded (n = 5163) and mild (n = 411), moderate (n = 226), and severe (n = 147) intrauterine growth retardation. Compared with non-growth-retarded infants of the same gestational age, growth-retarded infants had substantially lower lengths, head circumferences, and proportionality ratios, and the magnitude of the deficits increased significantly with increasing degrees of growth retardation. When the comparison was based on birth weight rather than gestational age, however, growth-retarded infants had slightly but significantly greater lengths and head circumferences, with increased variability in body proportions, but no evidence of the bimodality that would characterize two distinct subtypes. The analysis suggests that proportionality among intrauterine growth-retarded infants represents a continuum, with progressive disproportionality as severity of growth retardation increases. Moreover, despite evidence of some "sparing," the absolute magnitudes of the deficits in length and head growth remain substantial.

Diurnal variation in admission to hospital of women in labour.

In women having spontaneous labour or premature rupture of the membranes there is a marked diurnal variation in times of admission to hospital. Analysis of 4755 nulliparous women with single pregnancies in cephalic presentation at term, indicated that they presented in labour or with premature rupture of the membranes nearly twice as frequently during the night as during the evening. The peak hours for delivery were late morning and afternoon. The authors discuss previously published reports of similar findings and of a diurnal variation in maternal hormone levels in humans and experimental animals. The potential clinical importance of this phenomenon is considered.

The validity of gestational age estimation by menstrual dating in term, preterm, and postterm gestations.

Despite recognition that estimation of gestational age (GA) based on maternal recollection of the last normal menstrual period (LNMP) is fraught with error, it is not generally appreciated that the magnitude and direction of this error vary as a function of the LNMP estimate. Early second-trimester (16 to 18 weeks) ultrasound determinations of the fetal biparietal diameter were used as the "gold standard" to test the validity of LNMP-based GA estimates in 11,045 women. The large majority of deliveries occurring at or near term showed LNMP estimates that were valid within plus or minus seven days of the ultrasound estimate. As the LNMP GA deviated progressively toward earlier or later GAs, however, the discrepancies became quite marked, especially for postterm dates. The positive predictive values of the LNMP GA estimates decreased dramatically from term (.949) to preterm (.775) to postterm (.119) deliveries. These systematic errors in menstrual GA estimates have profound implications for unnecessary induction, dysfunctional labor and cesarean section, and resultant neonatal and maternal morbidity.

Obstetric consequences of postmaturity.

The obstetric management of 340 pregnancies delivered 2 or more weeks postterm and 1408 pregnancies delivered at 41 weeks is compared with that of 5915 pregnancies delivered at 39 to 40 weeks. In all patients menstrual dating was confirmed by early ultrasonographic examination. Postterm labor in primiparas resulted in a high cesarean section rate because of failure to progress; this increased rate was observed even after controlling for induction of labor and the size of the infant. We suggest that primiparas who go postterm often have increased uterine dysfunction. Uterine dysfunction accounts for the increase in the cesarean section rate and is a partial explanation for "failed" inductions.

Assessment of fetal risk in postdate pregnancies.

To assess postdate fetal risk, pregnancies in which menstrual history was confirmed by early ultrasound examination were reviewed; 5915 pregnancies within 1 week of term, 1408 1 to 2 weeks postdate, and 340 at least 2 weeks postdate. Fetal distress and meconium release were twice as frequent and meconium aspiration eight times as frequent postterm. Birth asphyxia was unrelated to gestational age. Fractures and palsies were more frequent because of primiparity and macrosomia. Only one antepartum fetal death occurred in 1748 postdate pregnancies. Review of 674 perinatal deaths at 37 plus weeks in Quebec showed no increase in deaths postterm. The increase in fetal distress and meconium aspiration postterm without an increase in birth asphyxia or fetal death may reflect greater responsiveness of the more mature fetus to mild asphyxic insults. Findings of this study could not justify increased fetal monitoring in postdate pregnancies.

Respiratory distress syndrome in second-born versus first-born twins. A matched case-control analysis.

The well-known increased risk of the respiratory distress syndrome in a twin born second as compared with the twin born first is usually attributed to the second twin's predisposition to depression at birth ("asphyxia"). We analyzed the etiologic roles of birth order, presentation, and depression at birth in the development of the respiratory distress syndrome in matched case-control populations drawn from 221 preterm twin pairs. Among the 39 twin pairs discordant for respiratory distress syndrome, the second twin was the affected member in 31 pairs. Second birth order was the only independent risk factor, but only in vaginal deliveries (matched odds ratio, 14.2; 95 percent confidence interval, 2.5 to 81.1). Second twins delivered abdominally did not have an increased risk relative to first twins (odds ratio, 0.9; confidence interval, 0 to 17.8). When depression at birth was evaluated as an outcome variable, malpresentation, rather than birth order, was the major risk factor (independent matched odds ratios of 2.7 [confidence interval, 1.0 to 7.5] and 1.3 [0.7 to 2.5], respectively). Thus, second twins' increased risk of respiratory distress syndrome cannot be explained by a predisposition to depression at birth; a more important factor may be that second twins do not benefit from the salutary effects of labor to the same extent as first twins.

Temporal variation in rates of cesarean section for dystocia: does "convenience" play a role?

The purpose of this study is to test the hypothesis that convenience for the physician plays a role in the rate of cesarean section performed because of dystocia. Three time periods were defined (night, 12 midnight to 7:59 AM; day, 8 AM to 5:59 PM; evening, 6 PM to 11:59 PM) based on the work commitments and daily routines of the obstetrician. Rates of cesarean section for dystocia were determined for each of the three time periods. An evening peak in the cesarean section rate is partially but not entirely explained by an evening increase in the proportion of patients in prolonged labor. When patients were stratified according to labor duration (less than 12, 12 to 15, and greater than 16 hours), a persistent evening excess in the rate of cesarean section for dystocia was observed for patients whose labor duration was less than 16 hours. Although this is interpreted as being consistent with the hypothesis of physician convenience, the magnitude of this effect on the overall rate of cesarean section for dystocia is small.

Failed forceps.

Among 53 cases of failed forceps occurring in 6524 uncomplicated primiparous deliveries, depression at birth and encephalopathy occurred with similar frequency as when cesarean section was done for failure to progress in the second stage, and birth trauma was no more common than that with successful midforceps delivery. Factors predisposing to or associated with midforceps deliveries or second stage cesarean sections were short mothers, heavy babies, induced or prolonged labors, and fetal distress or meconium release in labor.

Birth asphyxia, trauma, and mortality in twins: has cesarean section improved outcome?

The outcome of two populations of twins delivered at the same hospital, numbering 554 in 1963 to 1972 and 614 in 1978 to 1984, was reviewed to determine the factors contributing to depression at birth, trauma, and mortality in each period. The cesarean section rate had increased from 3% in the early period to 51% in the later period, with 92% of the later cases in which the first twin presented abnormally being delivered by cesarean section. Among infants of greater than 28 weeks' gestation the incidence of severe depression at birth was not reduced with the increased cesarean rate, remaining at 2% in both populations; none developed encephalopathy or died as a result of birth asphyxia or trauma. Neonatal mortality was markedly reduced in the second period, primarily because of a reduction in deaths resulting from respiratory distress syndrome. It is not possible to show that the marked increase in the rate of cesarean delivery has improved the condition of twin infants at birth.

Has use of cesarean section reduced the risks of delivery in the preterm breech presentation?

The effect of cesarean section on the condition at birth in cases of preterm breech presentation was studied in consecutively delivered infants in two time periods. Delivery was rarely (8%) by cesarean section in 1961 to 1974 and usually (89%) by cesarean section in 1978 to 1984. The increased cesarean rate did not reduce the incidence of severe depression, which was double that in control cases with cephalic presentations in both periods. Breech births did not have a higher mortality rate than cephalic births in either period; birth trauma and encephalopathy were similar in both periods. Cesarean section was therefore not found to reduce either the incidence of depression at birth or the mortality. However, head entrapment was responsible for the deaths of seven of 55 live-born infants delivered vaginally at 25 to 28 weeks' gestation, all weighing less than 1000 gm. Although cesarean section is at present performed least often among these extremely premature infants, it is in these cases that it may prove most beneficial.

Changing patterns of birth asphyxia and trauma over 20 years.

Comparison of birth asphyxia and trauma in the same obstetric service during periods 18 years apart shows some reassuring and some disquieting findings. Liberalized cesarean sections, electronic monitoring of fetal heart in labor, and replacement of opiate sedation by epidural anesthesia have had their effect. There has been dramatic reduction in perinatal death and neonatal encephalopathy due to birth asphyxia and trauma and only rarely do affected infants now develop permanent cerebral injury. Severe birth asphyxia, defined by need for prolonged ventilation, has, however, remained unchanged in frequency. Unexpectedly, fractures and paralyses have dramatically increased. The major hazard today for the term infant is the use of midforceps, which has become much more common in parallel with the increased use of pain relief by continuous epidural anesthesia.

Hazards and benefits of elective induction of labor.

Labor, delivery, and newborn course were studied in 621 pregnancies in which labor was electively induced at or after 39 weeks, and in 3,851 control pregnancies in which the onset of labor was spontaneous. Induced labors were not prolonged, nor was the duration of ruptured membranes. Fetal distress and birth asphyxia were not more frequent after induction, and release of meconium occurred much less frequently (9.3% for induced labor versus 16.7% for spontaneous). There was greater use of epidural analgesia and of forceps delivery in induced labor. Among primiparous patients, cesarean delivery for "failure to progress" was performed in 14% of electively induced labors and 7% of spontaneous control labors, a difference not noted among multiparous patients who had a primary cesarean birth rate of less than 2%. Iatrogenic prematurity was not a problem; none of the 621 infants who was born after elective induction developed respiratory distress syndrome, and only one weighed less than 2,500 gm.

Fetal macrosomia: prediction, risks, proposed management.

The outcome of delivery of infants weighing more than 4000 g born during two time periods 15 years apart was studied retrospectively. The increased use of cesarean section and other obstetric advances did not reduce the risk of fetal asphyxia and trauma associated with large fetal size. Maternal factors were identified for risk categorization of fetal macrosomia during pregnancy. Macrosomia was rare at 37 weeks and increasingly common thereafter. Fetal size assessment by ultrasound at 36 to 38 weeks' gestation would permit induction of labor for the macrosomic infant before the size became excessive or would make the accoucheur aware of the dangers that may arise during delivery.