Frances H. McLean

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.

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.

Risk of respiratory distress syndrome related to gestational age, route of delivery, and maternal diabetes.

Abstract From this analysis, respiratory distress syndrome appears to be a condition related to prematurity, exacerbated by cesarean section delivery, and unaffected by maternal diabetes. The incidence and mortality rate are inversely related to gestational age with the syndrome probably rarely, if ever, occurring after 38 weeks. Cesarean section is associated with a markedly increased incidence and mortality rate. The incidence of respiratory distress syndrome in infants of diabetic mothers is the same as in infants of nondiabetic mothers when delivered at the same gestational age and by the same route. When premature delivery is considered for maternal or fetal complications, it should, whenever possible, be effected vaginally rather than by cesarean section.

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.

Has an increased cesarean section rate for term breech delivery reduced the incidence of birth asphyxia, trauma, and death?

To evaluate whether the dramatic rise in the cesarean section rate for breech presentation (from 22% in the decade 1963 to 1973 to 94% in 1978 and 1979) has been justified, 770 term breech deliveries at the Royal Victoria Hospital during the period 1963 to 1973 and during 1978 and 1979 have been reviewed. Neonatal outcome, as determined by one neonatologist during the entire period of this study, was analyzed according to vaginal or cesarean section breech deliveries of primiparous and multiparous women. For each method of delivery and state of parity the occurrence of asphyxia neonatorum, abnormal cerebral signs, postasphyctic congenital heart failure or renal failure, and intrapartum and neonatal deaths was studied. The most severe cases were individually reviewed. While breech presentation has become a virtual indication for cesarean section in many centers, to date , there has not been an evaluation of how effective this procedure is in reducing birth asphyxia and trauma. In this study we assessed whether the trend to perform cesarean section in all term breech presentations is justified and whether neonatal morbidity and mortality rates have actually improved as a result.

Respiratory distress syndrome in infants delivered by cesarean section

Abstract The incidence of respiratory distress syndrome in 536 infants consecutively delivered by cesarean section was found to be 8 per cent. The incidence was 21 per cent among infants delivered by cesarean section for indications with a high risk to the fetus in utero, nil among infants delivered for middle risk indications, and 7.5 per cent among infants delivered for low risk indications. These differences in incidence were found to be solely accounted for by differences in gestational age of infants delivered for the three groups of indications. Respiratory distress syndrome developed in 69 per cent of those delivered by cesarean section at 29 to 33 weeks, in 41 per cent at 34 to 36 weeks, in 9.4 per cent at 37 to 38 weeks, and in only 2 infants out of 361 delivered after 38 weeks (after 270 days of gestation). At any one gestational age the incidence of respiratory distress syndrome was the same regardless of the indication for which cesarean section was performed. Of the infants delivered by cesarean section, 28 per cent of those with respiratory distress syndrome and 1.9 per cent of those without this syndrome died. Comparing the incidence of respiratory distress syndrome among infants of the same gestational age delivered per vaginam and by cesarean section, it was found that the incidence was increased three times at 31 to 33 weeks, seven times at 34 to 36 weeks, and 14 times at 37 to 38 weeks by cesarean section delivery. Cesarean section carries with it a strong predisposition to respiratory distress syndrome. This predisposition is related to the procedure itself, and not to the indications for which it is performed. Infants delivered after 270 days of gestation, whether by cesarean section or per vaginam, are not susceptible to respiratory distress syndrome with but 3 exceptions out of 14,459 consecutive livebirths.

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.

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.

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.

Fetal maturity: amniotic fluid analysis correlated with neonatal assessment.

Abstract The birth weights and gestational age assessments, in weeks of neonates have been compared with the creatinine level and the percentage of orange-staining cells in the amniotic fluid. In an attempt to verify the accuracy of these tests, two groups were analyzed, the first with the use of the last normal menstrual period as obtained by maternal history and the second with the use of the clinical assessment of the neonate within 24 hours of birth. Correlation was also carried out with birth weight. The accuracy of creatinine concentration and orange-staining cells is not disturbed in high-risk pregnancies. The creatinine level is more accurate for both gestational age and baby weight than the percentage of orange-staining cells. When the gestational age is around 36 weeks, creatinine values are reliable; if the gestational age is 38 weeks or more, the orange-staining cell count is more accurate. The clinical assessment of gestational age is very accurate and helpful. It improves the results obtained by correlation of the gestational age with the percentage of orange-staining cells.