The effect of birth interval on perinatal survival and birth weight

Although the effect of a short birth interval on the first child in a pair has received attention in the literature, the effect on the second child has received less. In this article the authors investigate the complex set of relationships between birth interval, maternal age and parity, and their effects on the birth weight and survival of the later-born child.The data consist of 12,995 singleton births to women of parity two or higher during1977 and 1978 in a single hospital. The outcome of the previous pregnancy is controlled by restricting the analysis to women whose previous pregnancy ended in a live infant who is still living at the time of the index birth.The effect of birth interval on birth weight and on survival is examined simultaneously(via logistic regression), with the effects of maternal age and parity. The risks of adverse outcomes as a function of birth interval are estimated by adjusted odds ratios.After adjusting for maternal age and parity, interval was found to be an important precursor of both perinatal mortality and low birth weight. At all levels of maternal age and parity, babies born during a 9- to 12-month birth interval are at greater risk of low birth weight and/or perinatal mortality than babies born after a longer birth interval.     

Evaluation of antenatal risk scoring in a preterm birth prevention and perinatal loss

The study aim was to determine risk factors associated with preterm delivery, perinatal mortality, and neonatal morbidity among 687 indigent, pregnant women in their first term registered with the New Civil Hospital, Ahmedabad, India, between September, 1989, and March, 1991. Women were scored according to their level of risk: no risk, mild risk, moderate risk, and severe risk, from scores based on sociodemographic and obstetric data: pallor, maternal weight, 2 or more prior abortions, first pregnancy or 5 pregnancies, adolescent pregnancy, prior preterm birth, prior prenatal mortality or stillbirths. Out of 696 deliveries, there were 71 (10.2%) preterm births, of which 3 (2.38%) were among women within the no risk groups. There were 47 (11.10%) from the mild risk group and 20 (14.08%) from the moderate risk group. There were 20% from the severe risk group. Perinatal mortality was 84.77/1000 births, and 7.94 among the no risk group. The perinatal mortality rate rose with level of risk, with 92.20 per thousand births for the mild risks to 200 for the severe risks, which was statistically significant. Neonatal morbidity also increased with the increased level of risk. Preterm birth was found not to be associated with pallor and prior history of stillbirth. Perinatal mortality was not associated with pallor and first pregnancy. Factors significantly associated with preterm births and perinatal mortality were maternal malnutrition, higher pregnancy order, older maternal age at delivery, and prior preterm births and fetal loss. Pregnant women with risk factors had greater relative risk of preterm birth and perinatal mortality by 5.01 and 13.09 times. With maternal risk factors, the risk increased by 80.05% and 92.35%. The risk factors were highly sensitive for preterm births (95.77%), but had low specificity (19.69%), and low positive predictive value (11.93%). Perinatal mortality sensitivity, specificity, and positive predictive values were 98.31%, 19.90%, and 10.34%n respectively. The findings differed from previously reported studies; scoring system used has a higher sensitivity to predicting preterm birth and perinatal mortality among high risk women, and poor sensitivity among low risk women. Moderate and mild could be identified with this system and referred for follow-up.     

Ethnic differences in perinatal mortality--a challenge.

The perinatal mortality rates of mothers who delivered at St. Thomas's Hospital from 1969 to 1976 have been examined. The rate in the West Indian population was significant higher than in the United Kingdom white population. The increased West Indian mortality was confined to infants with a birth weight of more than 2.0 kg and a gestational age of more than 37 weeks. The relative risk of perinatal death for West Indian mothers compared with UK white mothers was 1.4 at birth weights of 2.5 kg to 2.9 kg, rising to 4.3 at 4.0 + kg. West Indian perinatal mortality in term babies of normal birth weight was higher in all maternal age and parity groups except parity 3, but the difference was greatest in women aged 30 or over. The African perinatal mortality rate was not significantly greater than the UK white rate although it followed the West Indian trends. Pre-eclampsia and forceps delivery were associated with a greatly increased perinatal mortality in West Indian babies. The excess West Indian mortality could not be explained completely by differences in the proportions of stillbirths and early neonatal deaths nor by the distribution of births by parity, maternal age, or social class. Possible explanations for the differences in mortality are discussed.     

Families with a perinatal death: is there an association between the loss and the birthweight of surviving siblings?

Our objective was to study birthweight among surviving siblings in families with and without a perinatal loss, and to evaluate whether different causes of death were associated with the results. Data were for 1967-98 from the Norwegian Medical Birth Registry. Births were organised with the mother as the observation unit through the personal identification number, providing sibship files. We analysed 550 930 sibships with at least two singletons, 208 586 sibships with at least three singletons and 45 675 sibships with at least four singleton births. We compared mean birthweight and gestational age between infants in sibships with and without a perinatal loss, total losses and the different causes of death. Surviving siblings in families with a perinatal loss had significantly lower mean birthweights than their counterparts in unaffected families, after adjusting for gestational age, interpregnancy interval, time period and marital status. An exception was found when cause of death was a birth defect, when growth retardation among surviving siblings was not found on average. We conclude that families who have lost an infant because of a birth defect do not appear to have an increased risk of adverse birth outcome associated with growth restriction.     

Twinning rates and survival of twins in rural Nepal

BACKGROUND: Twin pregnancies are common but there are few data on rates of twinning or survival of liveborn twin infants in developing countries. METHODS: The rates of multiple births were calculated in a population-based cohort of married women of childbearing age who were enrolled in a randomized community trial to assess the impact of vitamin A or beta-carotene on maternal and infant health and survival. RESULTS: The rate of twinning was 16.1 per 1000 pregnancies (7.4 if only twin pregnancies resulting in two liveborn infants were used). The rate for triplets and quadruplets was 0.19 and 0.06 per 1000 pregnancies. Twinning rates were higher among women of higher parity, but were not associated with maternal age. Twinning rates among twins where at least one was live born (or increased in utero survival) were 30% (95% CI : -1%, 71%) and 44% (95% CI : 9%, 89%) higher among women receiving vitamin A and beta-carotene supplements than placebo, after adjusting for maternal age, gestational age, and parity. The perinatal mortality rate was 8.54 times higher for twins than singletons, 7.32 higher for neonatal mortality, and 5.84 higher for cumulative 24-week mortality. This difference was reduced but not erased by adjusting for gestational age. No difference in survival of liveborn twin infants was seen by supplement group. A higher mortality rate among male twins was largely explained by gestational age. CONCLUSIONS: Multiple births are relatively common occurrences in rural Nepal, and carry a much higher mortality risk for the infants than for singletons. Vitamin A or beta-carotene supplementation appeared to increase the rate of twinning, or improve the survival of twins in utero, but did not increase twin survival after birth.     

Risk factors for perinatal deaths in rural Bangladesh

Perinatal mortality refers to stillbirths and deaths which occur during the first week of life. 7 million such deaths occur annually worldwide, almost all of which are in developing countries. Rates as high as 75-100 deaths/1000 births have been documented in developing countries. The 3 leading causes of perinatal mortality are complications of pre-term birth, birth asphyxia and birth trauma, and bacterial infections. The other causes of perinatal mortality are largely unknown due to difficulties in documenting stillbirths in developing countries. In many developing country societies, it is culturally unacceptable to acknowledge a birth until it has survived its first week of life. This study identified and quantified the risk factors for perinatal deaths in a rural community in Manikganj district, Bangladesh. Cases were mothers whose infants died in the perinatal period, while comparison mothers were those whose infants survived the perinatal period. Of the 186 infant deaths recorded, 130 (69.9%) were in the perinatal period, and included 53 stillbirths. The perinatal death rate was 64.5/1000 births. Logistic regression confirmed that maternal age, parity, and mal-presentation were significantly associated with perinatal deaths. Mal-presentation was independently associated with a increased risk of perinatal death.     

Selective fertility and the distortion of perinatal mortality

Data from the Medical Birth Registry of Norway, covering more than one million births for the period 1967-1984, were used to study the magnitude and effects of selective fertility, which is the tendency for a woman to replace a perinatal loss. Variation in fertility after the first three births is studied, controlling for perinatal outcome of previous births, maternal age, and year of birth. Even after the first birth, fertility is higher after a perinatal loss. Selective fertility is more strongly present at each successive birth order, and at each birth order it is stronger among older women. As the average number of births per woman decreases, the force of selective fertility increases; that is, its importance has increased over time. Perinatal mortality at the third and fourth birth orders is particularly distorted by the mechanism of selective fertility in studies based on cross-sectional data. Mortality at second birth is exaggerated by 1%, at third birth by 8% to 20%, and at fourth birth by 18% to 27%, with the largest effects seen in the later periods. A major portion of the increase in perinatal mortality from the second to fourth birth seen in most studies based on cross-sectional data can be explained by the mechanism of selective fertility.     

Changing risks of stillbirth and neonatal mortality associated with maternal age in Western Australia 1984-2003

There has been a trend over the past two decades in some Western countries for women to delay childbearing, a factor associated with an increased risk of perinatal mortality (stillbirth and neonatal death). While the rates of stillbirth and neonatal mortality have improved in some countries, it has not been established whether maternal age remains a risk factor for perinatal mortality in Australia. The Western Australian Maternal and Child Health Research Database (MCHRDB) was used to examine the effect of maternal age on perinatal death in the periods 1984-93 and 1994-2003 after adjustment for parity and sociodemographic factors. Stillbirths and neonatal deaths were analysed separately. The crude rate of stillbirth has shown little change over the 20 years examined remaining at around 7.5 per 1000 total births, while the rate of neonatal death has decreased steadily from 5.4 per 1000 livebirths in 1984 to 2.0 in 2003. Older maternal age remains a risk factor for stillbirth but the relative risk has declined. After adjustment for parity and sociodemographic factors the relative risk of stillbirth for a woman aged over 40 years (compared with a woman aged 25-29 years) decreased from 2.6 in the period 1984-93, to 1.9 in the period 1994-2003. The increased risk of stillbirth associated with teenage mothers was fully explained by sociodemographic factors in both time periods. No increased risk of neonatal death was evident in the recent period 1994-2003 for teenage or older mothers after adjustment for parity and sociodemographic factors. In spite of some improvements over the past 20 years, women 30 years of age and older continue to be at increased risk of stillbirth. The risk of neonatal death is no longer associated with increased maternal age; however, the small number of cases in the older maternal age groups may be a result of the increased prevalence of antenatal screening and terminations for birth defects.     

Predictors of foetal and neonatal mortality in Cura?ao, Netherlands Antilles. A multivariate analysis

In Cura?ao a systematic and comprehensive investigation of numerous factors, potentially associated with an increased risk of foetal and neonatal mortality, was carried out in a 2-year period (1984-85). The inquiry was restricted to singleton births. Data on 205 women who experienced pregnancy loss were compared with those on 913 women who did not sustain foetal or neonatal loss. Data comprised information on maternal characteristics, clinical course of pregnancy and delivery, and neonatal characteristics. Of 130 factors measured, 14 were entered into a multivariate analysis. From the analysis 5 risk factors emerged as significant predictors of mortality: gestational age, birth weight, sex, foetal presentation and congenital anomalies. Factors such as social class, marital status, maternal age and parity were not associated with an increased risk of foetal and neonatal mortality in Cura?ao.     

Determinants of perinatal and infant mortality in Italy.

Determinants of stillbirths, perinatal and infant mortality in Italy have been analyzed using information collected routinely by the Italian Central Institute of Statistics on more than 2,400,000 births and 33,000 infant deaths in the period 1980-1983. Individual records included data on maternal (i.e. age, education, obstetric history) and fetal characteristics (sex, birth weight, gestational week at birth). The Italian stillbirth, perinatal and infant (1st-365th day of life) mortality rates in the period considered were respectively 7.7/1000 births, 16.4/1000 births and 13.5/1000 livebirths. Perinatal and infant mortality was extremely elevated in the very-low-birth-weight category. About 90% of liverbirths weighing less than 1000 g died within the first year of life, but this fell to about 45% in babies weighing 1000-1499 g. Among other factors, stillbirth, perinatal and infant mortality rates were elevated among males, born to older women and in higher birth rank and multiple pregnancies. These findings persisted, although less markedly, after adjustment for weight. Mortality rates were about 50-70% higher in less educated women. This finding was not markedly changed after adjustment for birth weight and maternal age, suggesting that socio-economic factors are per se important determinants of perinatal and infant mortality in Italy.     

The effect of parental age, birth order and other variables on early childhood mortality: a Caribbean example.

The 4275 births to women of native ancestry that took place on the island of St Barthélemy, French West Indies between 1878 and 1970 were analyzed according to the sex of the child, the year of birth, maternal age, maternal parity, paternal age and the number of children the father already had to determine the effects of these variables on rates of perinatal death, death before age 1 and death before age 5. The year of birth, the number of children the father already had, and maternal parity influenced death before age 1 and death before age 5. The sex of the child also influenced the probability of dying in the first year of life but not the first 5 yr of life when the other variables were controlled. Perinatal deaths were influenced only by the sex of the child, but even this effect disappeared when the other variables were controlled.     

Recurrence of gestational age in sibships: implications for perinatal mortality.

The authors studied the extent to which preterm birth and perinatal mortality are dependent on the gestational ages of previous births within sibships. The study was based on data collected by the Medical Birth Registry of Norway from 1967 to 1995. Newborns were linked to their mothers through Norway's unique personal identification number, yielding 429,554 pairs of mothers and first and second singleton newborns with gestational ages of 22-46 weeks, based on menstrual dates. Siblings' gestational ages were significantly correlated (r = 0.26). The risk of having a preterm second birth was nearly 10 times higher among mothers whose firstborn child had been delivered before 32 weeks' gestation than among mothers whose first child had been born at 40 weeks. However, perinatal mortality in preterm second births was significantly higher among mothers whose first infant had been born at term, compared with mothers whose firstborn child was delivered at 32-37 weeks. Since perinatal mortality among preterm infants is dependent on the gestational age in the mother's previous birth, a common threshold of 37 weeks' gestation for defining preterm birth as a risk factor for perinatal death may not be appropriate for all births to all mothers.     

The determinants of the high Dutch perinatal mortality in a complete regional cohort, 1990-1994

OBJECTIVE: Analysis of the effects of population-based determinants (maternal age, parity, multiple pregnancy and ethnicity) and of professional and organisational factors (conservative management in case of early preterm birth, the policy on prenatal screening and the Dutch obstetric-care system in general) on perinatal mortality. DESIGN: Population-based prospective cohort study. METHOD: In a regional cohort (Zaanstreek) of 8031 pregnancies in the period 1990-1994 data were prospectively collected in an electronic database by deliverers of primary and secondary care. Analysis focussed on the effect on perinatal mortality of maternal age, parity, multiple pregnancy, ethnicity and professional and organisational factors (the policy in case of early preterm birth, the policy on prenatal screening and the Dutch obstetric-care system in general). Perinatal mortality was defined as mortality from a gestational age of 22 weeks until 28 days post partum. RESULTS: The perinatal mortality in the Zaanstreek was 12.6/1000. Increasing the gestational age to 28 weeks decreased the perinatal mortality by 29%. The perinatal mortality in this cohort was significantly affected by parity, multiple pregnancy and maternal age (relative risk: 2.8), but not by ethnicity if corrected for the previous factors. Conservative management in case of early preterm birth and a restrictive screening policy for lethal birth defects were associated with an increase in perinatal mortality. In 31 of 92 singleton pregnancies followed by perinatal mortality, a relationship to substandard care was established. In 7 cases this relationship was probable and in 1 case the midwife was responsible. CONCLUSION: Given the magnitude of their effects, both independently and via interaction, stratification for maternal age, parity, multiple pregnancy and ethnicity must precede any interpretation and comparison of perinatal mortality rates. Although clinical policy played a modest role, a negative role of the organisation of obstetric care was unlikely in this cohort. A definitive judgement as to the quality of perinatal care would require extension of the evaluation to at least the entire first year of life in connection with the morbidity. The most favourable effects can be expected from stimulatory measures directed at lowering the age at first pregnancy.     

The influence of maternal age on very preterm birth of twins: differential effects by parity

For singleton births, parity can modify the effect of maternal age on birth outcomes such as low birthweight and preterm birth; however, it is unknown whether this relationship exists for twin births. As the rate of twin births increases among older women, it is important to understand how parity may influence the relationship between maternal age and adverse birth outcomes. The NCHS Matched Multiple Birth Data Set, which contains all twin births in the USA from 1995 to 1998, was analysed. Parity was grouped into two levels (primiparous--no prior live births, and multiparous--at least one prior live birth), and maternal age was divided into the following groups: 20-24, 25-29, 30-34, 35-39, and 40 years or more. Very preterm birth was defined as births occurring before 33 weeks. Logistic regression was used to obtain odds ratios (OR) to estimate the risk of very preterm birth, and to determine the relationships between parity, maternal age, and very preterm birth. Among primiparae, women 40 years and older had a reduced risk of very preterm birth compared with women of 25-29 years (OR 0.74 [95% CI=0.66, 0.84]). Among multiparae, women 40 years and older had the same risk of very preterm birth compared with women of 25-29 years (OR 1.00 [95% CI=0.90, 1.12]). However, stratification by education revealed that the age gradient was limited to women with >12 years education among primiparae. The effect of maternal age on very preterm birth of twins differs according to parity. To some extent, that effect is further modified by education. Therefore, future analyses of maternal age and twin birth outcomes should account for measures of obstetric history and other factors, which may influence these results.     

Smoking in pregnancy as a risk factor for long-term mortality in the offspring

Summary. This study addresses the question of whether maternal smoking is related to postneonatal mortality and which are the contributing causes of death. Mortality of births in Sweden between 1 January 1983 and 31 December 1989 ( n = 714389) registered in the Medical Birth Registry was followed until 31 December 1990. The registry carries information on maternal smoking habits in early pregnancy. The Mantel-Haenszel procedure was used to control for confounding effects of maternal age, parity and year of birth: relative risks (95% confidence interval) associated with smoking were: 1.24 (1.17-1.31) for fetal death, 1.08 (1.01-1.16) for early neonatal death, 1.22 (1.08-1.39) for late neonatal death, 1.31 (1.23-1.41) for postneonatal mortality during the first year, and for the period between 1 and 8 years of age it was 1.19 (1.06-1.32). When birth-weight was controlled for, the increased relative risk for postneonatal mortality during the first year disappeared. Mortality between 1 and 8 years still showed an elevated risk of 1.43 (1.00–2.06). In order to control for confounding by social factors, 1986 births were linked to data from the 1985 Swedish census. The measure used was the socio-economic index (SEI), which reflects the parental education level. When maternal, paternal or family SEI was controlled for, late neonatal death was not significantly related to maternal smoking, but postneonatal death still showed a significantly increased relative risk of about 1.35. Four causes of death based on International Classification of Diseases (ICD) 8 and 9 were significantly related to maternal smoking: sudden infant death syndrome, injuries and poisoning, perinatal causes and infections.     

Searching for socioeconomic risk factors in perinatal mortality in Kuwait: a case control study

The aim of this paper was to investigate whether socioeconomic factors such as parent's education, occupation, and income constitute risk factors in perinatal mortality after controlling for biological variables such as birth weight and length of gestation, and maternal factors such as age, parity and reproductive history. A case-control study covering all perinatal deaths in Kuwait was conducted for one year from 1 October, 1997 to 30 September, 1998. Each case (perinatal death) was matched with a control (live birth). Matching criteria were: father's nationality, place, and date of birth. Information was successfully collected on 463 matched pairs, 274 Kuwaitis and 189 non-Kuwaitis. Only singleton births were included in the analysis. Bivariate analysis showed that several of the socioeconomic variables (e.g. lower education, lower income) increased the risk of a perinatal death. However, none of these variables remained significant in the multivariate analysis in which birth weight and length of gestation emerged as the two major determinants of perinatal deaths among both nationality groups. Among the Kuwaitis, primiparity and high parity, and previous history of miscarriage were also significant risk factors. Among the non-Kuwaitis, none of the socioeconomic factors, or the maternal factors, were significant predictors of perinatal mortality. For Kuwaitis, it appears that the government's policies and programs aimed at reducing social inequalities in the society have been effective in eliminating perinatal mortality differences between socioeconomic groups. Among non-Kuwaitis, the lack of differences is reflective of the fact that this group is relatively homogenous and selective of the more affluent who can bring the family to Kuwait. Both nationality groups benefit from the government's free health services. However, charges for non-Kuwaitis are due to be levied soon which may increase disparities in access to health care.     

中国3省市21家医院早产发生的相关因素及结局研究

目的 分析早产发生的影响因素与结局,为早产的防治工作提供依据. 方法 对3省市21家医院完成分娩的全部产妇13 322例进行调查,计算早产发生率,分析早产发生的相关因素,比较早产儿与足月儿的新生儿结局. 结果 早产发生率为6.0％,其中晚期早产（孕周34～36周）占77.3％;导致早产发生危险增加的因素有年龄＜20岁、年龄＞35岁、在校读书年数＞12年、多胎、发生妊娠合并症;早产导致死胎或死产,低、极低出生体重,Apgar得分≤7分,进入新生儿重症监护室,出院前或生后7d内死亡的危险增加. 结论 早产是威胁胎儿及新生儿健康的重要因素,应尽早识别具备早产危险因素的孕妇,以便及时开展针对性的治疗工作.     

Perinatal mortality in Shanghai: 1986-1987.

The incidence of, and risk factors associated with, perinatal mortality in Shanghai during 1986-1987 are examined using data from a multi-site study conducted in 29 hospitals. The overall perinatal mortality rate was 14.96 per 1000 births. The mortality rates of antepartum fetal death, intrapartum fetal death and early neonatal death were 5.97, 2.06 and 6.94 per 1000 births, respectively. The perinatal mortality rates increased in winter and late spring. Male neonates were 1.5 times more likely to die than females. Low birthweight and preterm infants had 15 to 80 times higher risk of perinatal death. Higher parity, multiple pregnancy, and maternal age greater than or equal to 35 years were the risk factors for perinatal mortality. Asphyxia, cord complications, and congenital malformations were found to be the major causes of perinatal deaths. Comparison of mortality rates between Shanghai and the US suggests that the shortage of advanced technology in perinatal care (e.g. neonatal intensive care units) is a major obstacle to the reduction of perinatal mortality in Shanghai.     

Obstetric profiles and perinatal mortality among Pacific Island immigrants in New South Wales, 1990-93

OBJECTIVES: To describe the obstetric profile and perinatal mortality of Pacific Island-born women giving birth in New South Wales (NSW) and assess risk factors associated with the high perinatal death rate previously noted in this immigrant group. METHOD: Retrospective cohort study based on the Midwives Data Collection in NSW from 1990 to 1993. Births to 5,034 Pacific Island-born women were compared with births to 256,843 Australian-born women. RESULTS: Pacific Island-born women had fewer teenage pregnancies and were of an older age and higher parity. They were more likely to be married or in a de facto relationship and to present for antenatal care later in the pregnancy. The proportion of low birthweight and preterm birth was similar in the two groups but Pacific Islanders had a higher perinatal mortality rate (14.6/1,000 vs. 10.3/1,000, RR = 1.42, 95% CI = 1.13-1.54). Even at normal and high birthweights, infants of Pacific Island-born women were at greater risk of perinatal death. After adjusting for maternal factors (marital status, insurance status, parity and maternal age) Pacific Islanders were 30% more likely to have a perinatal death (OR = 1.30, 95% CI 1.07-1.54). CONCLUSIONS: Further analyses of the causes of perinatal death in Pacific Island-born women are needed so appropriate interventions can be implemented. IMPLICATIONS: The need for the design and evaluation of culturally specific services aimed at improving antenatal care attendance in Pacific Islanders is emphasised. Conventional risk assessment may not adequately predict adverse perinatal outcomes in all populations.     

Perinatal mortality in relation to birthweight and gestational age: a registry-based comparison of Northern Norway and Murmansk County, Russia

The objective was to explore how perinatal mortality relates to birthweight, gestational age and optimal perinatal survival weight for two Arctic populations employing an existing and a newly established birth registry. A medical birth registry for all births in Murmansk County of North-West Russia became operational on 1st January 2006. Its primary function is to provide useful information for health care officials pertinent to improving perinatal care. The cohort studied consisted of 17,302 births in 2006-07 (Murmansk County) and 16,006 in 2004-06 (Northern Norway). Birthweight probability density functions were analysed, and logistic regression models were employed to calculate gestational-age-specific mortality ratios. The perinatal mortality rate was 10.7/1000 in Murmansk County and 5.7/1000 in Northern Norway. Murmansk County had a higher proportion of preterm deliveries (8.7%) compared to Northern Norway (6.6%). The odds ratio (OR) of risk of mortality (Northern Norway as the reference group) was higher for all gestational ages in Murmansk County, but the largest risk difference occurred among term deliveries (OR 2.45, 95% confidence interval 1.45, 4.14) which hardly changed on adjustment for maternal age, parity and gestation. Proportionately, more babies were born near (± 500 g) the optimal perinatal survival weight in Murmansk County (67.2%) than in Northern Norway (47.6%). The observed perinatal mortality was higher in Murmansk County at all birthweight strata and at gestational ages between weeks 25 and 42, but the adjusted risk difference was most significant for term deliveries.