Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies

doi:10.1067/mob.2001.109735

American Journal of Obstetrics and Gynecology

Volume 184, Issue 3, February 2001, Pages 489-496

https://doi.org/10.1067/mob.2001.109735 Get rights and content

Abstract

Objective: This study was undertaken to estimate the cumulative risk of perinatal death associated with delivery at each gestational week both at term and post term. Study Design: The numbers of antepartum stillbirths, intrapartum stillbirths, neonatal deaths, and surviving neonates delivered at between 37 and 43 weeks’ gestation in Scotland, 1985-1996, were obtained from national databases (n = 700,878) after exclusion of multiple pregnancies and deaths caused by congenital abnormality. The numbers of deaths at each gestational week were related to appropriate denominators: antepartum stillbirths were related to ongoing pregnancies, intrapartum stillbirths were related to all births (excluding antepartum stillbirths), and neonatal deaths were related to live births. The cumulative probability of perinatal death associated with delivery at each gestational week was estimated by means of life-table analysis. Results: The gestational week of delivery associated with the lowest cumulative risk of perinatal death was 38 weeks’ gestation, whereas the perinatal mortality rate was lowest at 41 weeks’ gestation. The risk of death increased more sharply among primigravid women after 38 weeks’ gestation because of a greater risk of antepartum stillbirth. The relationships between risk of death and gestational age were similar for the periods 1985-1990 and 1991-1996. Conclusion: Delivery at 38 weeks’ gestation was associated with the lowest risk of perinatal death. (Am J Obstet Gynecol 2001;184:489-96.)

Section snippets

Population

The numbers of singleton births at each gestational week at term and after term in Scotland were obtained through analysis of the Scottish Morbidity Record (maternity), a national database of pregnancy information that has been >99% complete since the late 1970s,¹¹ between 1985 and 1996. Gestational age at birth was recorded in completed weeks’ gestation and was calculated from the estimated date of delivery in each woman’s clinical record, derived from her menstrual history and adjusted for

Results

There were 700,878 singleton births at 37 to 43 weeks’ gestation, excluding perinatal deaths caused by congenital abnormality, in Scotland between 1985 and 1996. Among this group there were 1230 antepartum stillbirths, 217 intrapartum stillbirths, and 425 neonatal deaths. There was no significant correlation (among primigravid women) between year of the birth and the proportion in whom labor was induced (overall, 25.8% had labor induced; r ² vs year = 0.1; P =.22) or the proportion delivered at

Comment

A range of denominators have been used to estimate the probability of perinatal death in relation to gestational week, including all births⁶ and all ongoing pregnancies.4, 16 In this study the probabilities of different types of perinatal death were estimated with different denominators, and the different consequences of antepartum and intrapartum obstetric events were taken into account. These probabilities were summed, and the cumulative probability of perinatal death associated with birth at

Acknowledgements

I am grateful to Dr James W.T. Chalmers of the Information and Statistics Division, National Health Services in Scotland, Edinburgh, for providing data from the Scottish Morbidity Record and the Scottish Stillbirth and Neonatal Death Enquiry.

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Stillbirth at term affects ∼1 per 1000 pregnancies at term in high income countries. A range of maternal characteristics are associated with stillbirth risk. However, given the low a priori risk of stillbirth, the vast majority of women with clinical risk factors would not experience a stillbirth in the absence of intervention. Stillbirth is the end point of multiple pathways, including both fetal growth restriction and fetal overgrowth. In most term stillbirths there is no mechanistic understanding of the cause of death and a sizeable proportion are completely unexplained. Term stillbirth is potentially preventable by early delivery, providing a rationale for screening. “Omic” analyses of blood taken prior to the onset of some of the conditions associated with stillbirth may help identify women at high risk and allow the potentially harmful intervention of early term medically indicated delivery to be targeted to the pregnancies most likely to benefit.
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This was an area-based, prospective cohort study on pregnancy at term with enrolled from 2014 to 2021 in Emilia-Romagna, a north Italian region. Data were retrieved from both birth certificates and the Stillbirth Surveillance system database. To identify independent risk factors, a multivariate analysis using logistic regression was performed. A descriptive analysis of the causes of stillbirth is also reported.
In the observation period, 246,437 babies born at term (including 260 stillbirths, giving a rate of 1.06/1000) were considered. The risk factors independently associated with stillbirth were small for gestational age babies (odds ratio, 2.58; 95% confidence interval, 1.88–3.53), pregnancy achieved though fertility treatments (odds ratio, 2.01; 95% confidence interval, 1.15–3.51), and delayed access to pregnancy services (odds ratio, 1.56; 95% confidence interval, 1.10–2.22). In multipara, the presence of a previous stillbirth (odds ratio, 3.91; 95% confidence interval, 1.98–7.72) was also associated with an increased risk for recurrence. Early- rather than late-term was an additional risk factor. The most frequent causes of death were placental and cord disorders (61/260 and 56/260, respectively). However, 28.1% of cases remain unexplained.
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Determining the optimal time of birth at term is challenging given the ongoing risks of stillbirth with increasing gestation vs the risks of significant neonatal morbidity at early-term gestations. These risks are more pronounced in small infants.
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This was a retrospective cohort study evaluating women with singleton, nonanomalous pregnancies at 37⁺⁰ to 40⁺⁶ weeks’ gestation in Queensland, Australia, delivered from 2000 to 2018. Rates of stillbirth, neonatal death, and severe neonatal morbidity were calculated for <3rd, 3rd to <10th, 10th to <25th, 25th to <90th, and ≥90th birthweight centiles. The composite risk of mortality with expectant management for an additional week in utero was compared with rates of neonatal mortality and severe neonatal morbidity.
Of 948,895 singleton, term nonanomalous births, 813,077 occurred at 37⁺⁰ to 40⁺⁶ weeks’ gestation. Rates of stillbirth increased with gestational age, with the highest rate observed in infants with birthweight below the third centile: 10.0 per 10,000 (95% confidence interval, 6.2–15.3) at 37⁺⁰ to 37⁺⁶ weeks, rising to 106.4 per 10,000 (95% confidence interval, 74.6–146.9) at 40⁺⁰ to 40⁺⁶ weeks’ gestation. The rate of neonatal mortality was highest at 37⁺⁰ to 37⁺⁶ weeks for all birthweight centiles. The composite risk of expectant management rose sharply after 39⁺⁰ to 39⁺⁶ weeks, and was highest in infants with birthweight below the third centile (125.2/10,000; 95% confidence interval, 118.4–132.3) at 40⁺⁰ to 40⁺⁶ weeks’ gestation. Balancing the risk of expectant management and delivery (neonatal mortality), the optimal timing of delivery for each birthweight centile was evaluated on the basis of relative risk differences. The rate of severe neonatal morbidity sharply decreased in the period between 37⁺⁰ to 37⁺⁶ and 38⁺⁰ to 38⁺⁶ weeks, particularly for infants with birthweight below the third centile.
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^☆: Supported by the Wellcome Trust.

^☆☆: Reprint requests: Gordon C.S. Smith, MD, University of Glasgow, Department of Obstetrics and Gynaecology, The Queen Mother’s Hospital, Yorkhill, Glasgow, United Kingdom G3 8SH.

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Fetus-Placenta-NewbornLife-table analysis of the risk of perinatal death at term and post term in singleton pregnancies☆,☆☆

Abstract

Section snippets

Population

Results

Comment

Acknowledgements

Lancet

Lancet

Post-term pregnancy: fetal considerations

Post-term pregnancy

Induction of labor confers benefits in prolonged pregnancy

BJOG

Prospective risk of stillbirth

Obstet Gynecol

Stillbirths and rate of neonatal deaths in 76,761 postterm pregnancies in Sweden, 1982-1991: a register study

Acta Obstet Gynecol Scand

Effects of maternal age, parity, and smoking on the risk of stillbirth

BJOG

Statistical analysis of epidemiologic data

Perinatal mortality in term and post-term births

Obstet Gynecol

Medical causes on stillbirth certificates in England and Wales: distribution and results of hierarchical classifications tested by the Office for National Statistics

BJOG

Scottish maternity and neonatal records

Fetus-Placenta-Newborn
Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies☆,☆☆