Early pregnancy predictors of preterm birth: the role of a prolonged menstruation-conception interval

Influence of different methods for calculating gestational age at birth on prematurity and small for gestational age proportions: a systematic review with meta-analysis

BACKGROUND

Recognizing premature newborns and small-for-gestational-age (SGA) is essential for providing care and supporting public policies. This systematic review aims to identify the influence of the last menstrual period (LMP) compared to ultrasonography (USG) before 24 weeks of gestation references on prematurity and SGA proportions at birth.

METHODS

Systematic review with meta-analysis followed the recommendations of the PRISMA Statement. PubMed, BVS, LILACS, Scopus-Elsevier, Embase-Elsevier, and Web-of-Science were searched (10-30-2022). The research question was: (P) newborns, (E) USG for estimating GA, (C) LMP for estimating GA, and (O) prematurity and SGA rates for both methods. Independent reviewers screened the articles and extracted the absolute number of preterm and SGA infants, reference standards, design, countries, and bias. Prematurity was birth before 37 weeks of gestation, and SGA was the birth weight below the p10 on the growth curve. The quality of the studies was assessed using the New-Castle-Ottawa Scale. The difference between proportions estimated the size effect in a meta-analysis of prevalence.

RESULTS

Among the 642 articles, 20 were included for data extraction and synthesis. The prematurity proportions ranged from 1.8 to 33.6% by USG and varied from 3.4 to 16.5% by the LMP. The pooled risk difference of prematurity proportions revealed an overestimation of the preterm birth of 2% in favor of LMP, with low certainty: 0.02 (95%CI: 0.01 to 0.03); I² 97%). Subgroup analysis of USG biometry (eight articles) showed homogeneity for a null risk difference between prematurity proportions when crown-rump length was the reference: 0.00 (95%CI: -0.001 to 0.000; I²: 0%); for biparietal diameter, risk difference was 0.00 (95%CI: -0.001 to 0.000; I²: 41%). Only one report showed the SGA proportions of 32% by the USG and 38% by the LMP.

CONCLUSIONS

LMP-based GA, compared to a USG reference, has little or no effect on prematurity proportions considering the high heterogeneity among studies. Few data (one study) remained unclear the influence of such references on SGA proportions. Results reinforced the importance of qualified GA to mitigate the impact on perinatal statistics.

TRIAL REGISTRATION

Registration number PROSPERO: CRD42020184646.

Association of Preterm Birth With Prescription of Psychotropic Drugs in Adolescence and Young Adulthood

IMPORTANCE

Individuals born preterm have increased risk of mental health impairment compared with individuals born at term. The associations between preterm birth and attention-deficit/hyperactivity disorder and autism are well established; for depression, anxiety, psychotic and bipolar disorder, studies show divergent results.

OBJECTIVE

To compare the prescription of psychotropic drugs in adolescence and young adulthood between those born preterm and those born at term.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used registry data to identify all Norwegians born after 23 weeks of completed gestation between 1989 and 1998. Included individuals were those without registered birth defects, alive at age 10 years, and with available maternal data. Individuals were followed up from 2004 to 2016. Psychotropic drug prescriptions received from age 10 to 23 years were compared between preterm groups and peers born at term. Individuals were compared with their siblings to control for shared family confounding. Data analyses were performed from August 2018 through February 2020.

EXPOSURES

Gestational age at birth (GA) was categorized in 4 groups: extremely preterm (GA, 23 weeks and 0 days to 27 weeks and 6 days), very preterm (GA, 28 weeks and 0 days to 31 weeks and 6 days), moderately or late preterm (GA, 32 weeks and 0 days to 36 weeks and 6 days), and full term (GA, 37 weeks and 0 days to 44 weeks and 6 days).

MAIN OUTCOMES AND MEASURES

Prescriptions of psychotropic drugs (ie, prescriptions specifically of psychostimulants, antidepressants, anxiolytics, hypnotics or sedatives, or antipsychotics or prescriptions of any of these 5 drugs) among preterm groups were compared with prescriptions among peers born at term and among siblings.

RESULTS

Among 505 030 individuals (259 545 [51.4%] males; mean [SD] birth weight, 3533 [580] g), 762 individuals (0.2%) were extremely preterm, 2907 individuals (0.6%) were very preterm, 25 988 individuals (5.1%) were moderately or late preterm, and 475 373 individuals (94.1%) were full term. Individuals born preterm had increased risk of psychotropic drug prescription, with a dose-response association between GA and prescription. The extremely preterm group had higher rates of prescription for all drug types compared with peers born at term, with odds ratios from 1.7 (95% CI, 1.4-2.1) for antidepressants to 2.7 (95% CI, 2.1-3.4) for psychostimulants. The elevated odds of prescription of all types were less pronounced in the moderately to late preterm group, including odds ratios of 1.1 (95% CI, 1.0-1.1) for antidepressants and 1.2 (95% CI, 1.1-1.2) for psychostimulants. The increases in odds were smaller in the sibling comparison, and increases were not significant for several groups. For example, the OR for any prescription in the sibling analysis was 1.8 (95% CI, 1.2-2.8) in the very preterm group and 1.0 (95% CI, 0.9-1.1) in the moderately or late preterm group.

CONCLUSIONS AND RELEVANCE

This cohort study found higher rates of prescription of psychotropic drugs throughout adolescence and young adulthood among individuals with all degrees of preterm birth compared with those born at term. These results provide further evidence for an increased risk of mental health impairment among individuals born preterm and suggest that this is not restricted to the most preterm groups.

Guideline No. 388-Determination of Gestational Age by Ultrasound

OBJECTIVE

To assist clinicians in assigning gestational age based on ultrasound biometry.

OUTCOMES

To determine whether ultrasound dating provides more accurate gestational age assessment than menstrual dating with or without the use of ultrasound. To provide maternity health care providers and researchers with evidence-based guidelines for the assignment of gestational age. To determine which ultrasound biometric parameters are superior when gestational age is uncertain. To determine whether ultrasound gestational age assessment is cost effective.

EVIDENCE

Published literature was retrieved through searches of PubMed or MEDLINE and The Cochrane Library in 2013 using appropriate controlled vocabulary and key words (gestational age, ultrasound biometry, ultrasound dating). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. There were no date restrictions. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The quality of evidence in this document was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

Accurate assignment of gestational age may reduce post-dates labour induction and may improve obstetric care through allowing the optimal timing of necessary interventions and the avoidance of unnecessary ones. More accurate dating allows for optimal performance of prenatal screening tests for aneuploidy. A national algorithm for the assignment of gestational age may reduce practice variations across Canada for clinicians and researchers. Potential harms include the possible reassignment of dates when significant fetal pathology (such as fetal growth restriction or macrosomia) result in a discrepancy between ultrasound biometric and clinical gestational age. Such reassignment may lead to the omission of appropriate-or the performance of inappropriate-fetal interventions.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Second-trimester fetal head circumference in more than 350 000 pregnancies: Outcome and suggestion for sex-dependent cutoffs for small heads

OBJECTIVE

To explore the relationship between small fetal second-trimester head circumference (HC) and pregnancy outcome and identify a cutoff point for offering genetic testing.

METHOD

Data from second-trimester scans in Denmark were linked to national registers. Fetuses with anomalies diagnosed before this scan were excluded. Fetuses were grouped according to HC z-score.

RESULTS

We included 352 515 singleton fetuses. The mean HC was significantly larger among males than among females with z-scores averaging 0.52 more in males. Small HC was associated with chromosomal anomaly, malformations of the CNS and heart, miscarriage/perinatal death, termination, preterm delivery, and intrauterine growth restriction (test for trend: P < .001 for all outcomes). Fetuses in the group with z-score less than -3 had the highest incidence of adverse outcome, irrespective of fetal sex. In the groups with z-scores between -3 and -2.5, and between -2.5 and -2, risk of adverse outcome was lower for females than males for all outcome categories.

CONCLUSION

Small HC in second trimester is a prognostic marker for adverse outcome. The smaller the HC, the higher the risk of adverse outcome. We suggest an HC cutoff point of -2 SD for males and -2.5 SD for females for offering genetic testing.

Stillbirth and preterm birth and associated factors in one of the largest cities in central Vietnam

AIM

Little is known about the rate of stillbirths, preterm births and associated risk factors in resource-limited settings like Vietnam. This study reports those rates for Da Nang, which is one of the largest cities in central Vietnam.

METHODS

Data on 20 762 births including stillbirths and preterm births and associated risk factors were prospectively collected from health facilities from April 2015 to March 2016.

RESULTS

The data represented 85% of the total births in Da Nang during the study period, and a stillbirth rate of 9.7 per 1000 live births was recorded. The preterm rate for live births was just under 5%. Independent factors associated with an increased risk of stillbirth and preterm births were mothers aged 35 plus, working as farmers, living in the provinces and a history of abortion. Mothers under 20 years with previous preterm births faced a higher risk of another preterm birth.

CONCLUSION

The stillbirth and premature birth rates in Da Nang were higher than rates in high-income countries. Developing registration programmes in Vietnam will provide improved data that will enable researchers and policymakers to identify strategies to reduce the number of stillbirths and premature births.

Discrepancy between pregnancy dating methods affects obstetric and neonatal outcomes: a population-based register cohort study

To assess associations between discrepancy of pregnancy dating methods and adverse pregnancy, delivery, and neonatal outcomes, odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for discrepancy categories among all singleton births from the Medical Birth Register (1995-2010) with estimated date of delivery (EDD) by last menstrual period (LMP) minus EDD by ultrasound (US) -20 to +20 days. Negative/positive discrepancy was a fetus smaller/larger than expected when dated by US (EDD postponed/changed to an earlier date). Large discrepancy was <10^th or >90^th percentile. Reference was median discrepancy ±2 days. Odds for diabetes and preeclampsia were higher in pregnancies with negative discrepancy, and for most delivery outcomes in case of large positive discrepancy (+9 to +20 days): shoulder dystocia [OR 1.16 (95% CI 1.01-1.33)] and sphincter injuries [OR 1.13 (95% CI 1.09-1.17)]. Odds for adverse neonatal outcomes were higher in large negative discrepancy (-4 to -20 days): low Apgar score [OR 1.18 (95% CI 1.09-1.27)], asphyxia [OR 1.18 (95% CI 1.11-1.25)], fetal death [OR 1.47 (95% CI 1.32-1.64)], and neonatal death [OR 2.19 (95% CI 1.91-2.50)]. In conclusion, especially, large negative discrepancy was associated with increased risks of adverse perinatal outcomes.

Different Risk Factors for Very Low Birth Weight, Term-Small-for-Gestational-Age, or Preterm Birth in Japan

From 1985 to 2013, the mean birth weight of infants in Japan decreased from 3120 g to 3000 g, and the low-birth-weight rate among live births increased from 6.3% to 9.6%. No prospective study has elucidated the risk factors for poor fetal growth and preterm birth in recent Japanese parents, such as increased parental age, maternal body figure, assisted reproductive technology (ART), and socioeconomic status. Participants were mother–infant pairs (n = 18,059) enrolled in a prospective birth cohort in Hokkaido, Japan from 2002 to 2013. Parental characteristics were obtained via self-reported questionnaires during pregnancy. Medical records helped identify very-low-birth-weight (VLBW; <1500 g), term-small-for-gestational-age (term-SGA), and preterm-birth (PTB; <37 weeks) infants. We calculated relative risks (RRs) for PTB, VLBW, and term-SGA birth based on parental characteristics. The prevalence of PTB, VLBW, and term-SGA was 4.5%, 0.4%, and 6.5%, respectively. Aged parents and ART were risk factors for PTB and VLBW. Maternal alcohol drinking during pregnancy increased the risk; a parental educational level of ≥16 years reduced risk of term-SGA. Maternal pre-pregnancy BMI of <18.5 kg/m² increased the risk of PTB and term-SGA. The RR for low BMI was highest among mothers who have low educational level. Among various factors, appropriate nutritional education to maintain normal BMI is important to prevent PTB and term-SGA in Japan.

Détermination de l'âge gestationnel par échographie

OBJECTIF

Aider les cliniciens à attribuer un âge gestationnel en fonction des résultats de la biométrie échographique.

ISSUES

Déterminer si la datation par échographie offre une évaluation plus précise de l'âge gestationnel que la datation en fonction des dernières règles avec ou sans recours à l'échographie. Offrir, aux praticiens et aux chercheurs du domaine des soins de maternité, des lignes directrices factuelles en matière d'attribution de l'âge gestationnel. Identifier les paramètres biométriques échographiques qui sont de fiabilité supérieure lorsque l'âge gestationnel est incertain. Déterminer la rentabilité de l'évaluation de l'âge gestationnel par échographie. RéSULTATS: La littérature publiée a été récupérée par l'intermédiaire de recherches menées dans PubMed ou MEDLINE et The Cochrane Library en 2013 au moyen d'un vocabulaire contrôlé et de mots clés appropriés (p. ex. « gestational age », « ultrasound biometry » et « ultrasound dating »). Les résultats ont été restreints aux analyses systématiques, aux essais comparatifs randomisés / essais cliniques comparatifs et aux études observationnelles rédigés en anglais. Aucune restriction n'a été appliquée en matière de dates. Les recherches ont été mises à jour de façon régulière et intégrées à la directive clinique jusqu'au 31 juillet 2013. La littérature grise (non publiée) a été identifiée par l'intermédiaire de recherches menées dans les sites Web d'organismes s'intéressant à l'évaluation des technologies dans le domaine de la santé et d'organismes connexes, dans des collections de directives cliniques, dans des registres d'essais cliniques et auprès de sociétés de spécialité médicale nationales et internationales.

VALEURS

La qualité des résultats est évaluée au moyen des critères décrits dans le rapport du Groupe d'étude canadien sur les soins de santé préventifs (Tableau 1). AVANTAGES, DéSAVANTAGES ET COûTS: L'attribution précise d'un âge gestationnel pourrait réduire l'incidence du déclenchement mené en raison d'une grossesse prolongée et améliorer les soins obstétricaux en nous permettant de planifier la chronologie des interventions nécessaires de façon optimale et d'éviter les interventions inutiles. Une datation plus précise permet l'optimisation de la tenue de tests prénataux de dépistage de l'aneuploïdie. Un algorithme national d'attribution de l'âge gestationnel pourrait atténuer les variations pancanadiennes en matière de pratique pour les cliniciens et les chercheurs. Parmi les désavantages potentiels, on trouve la réattribution possible des dates lorsqu'une pathologie fœtale importante (comme le retard de croissance intra-utérin ou la macrosomie) donne lieu à une divergence entre les résultats de la biométrie échographique et l'âge gestationnel clinique. Une telle réattribution pourrait mener à l'omission d'interventions fœtales justifiées ou à la tenue d'interventions fœtales injustifiées. DéCLARATIONS SOMMAIRES: RECOMMANDATIONS.

Smoking during pregnancy: A population-based study

AIMS

Tobacco is a major cause of disease and mortality in modern times. The risk of smoking in pregnancy is a serious threat to the development and future health of an unborn child. The aim of this study was to explore the epidemiological factors associated with smoking during pregnancy in a primary healthcare setting.

METHODS

All 856 maternity records at the Glaesibaer Health Care Centre in Reykjavik during 2006-2013 were reviewed and information on smoking habits investigated.

RESULTS

The records showed that in 108 (12.2%) pregnancies, women smoked at first visit and 63 stopped smoking in early pregnancy, leaving 45 (5.3%) mothers smoking throughout the whole gestational period. The mean age of the smoking women was 27.8 years and for the non-smokers 29.7 years. Low social status (odds ratio (OR) = 2.66; 95% confidence interval (CI): 1.19-5.96), previous mental health diagnosis (OR = 2.7; 95% CI: 1.3-5.6), and unstable relationship with a partner (OR = 3.78; 95% CI: 2.1-7.0) were associated with smoking. Smoking fewer cigarettes was associated with a 0.04-unit lower risk of smoking during pregnancy (OR = 0.04: 95% CI: 0.02-0.08).

CONCLUSIONS

Our results indicated that the women who smoked during pregnancy were often heavy smokers and living without a partner. They were younger, had worse mental health, and a lower social status than those pregnant women who did not smoke. Bearing in mind the consequence of smoking in pregnancy, this subgroup should get increased assistance to quit smoking before and during early pregnancy, as well as appropriate medical and social support.

Maternal height and the risk of preterm birth and low birth weight: a systematic review and meta-analyses

OBJECTIVE

Preterm birth (PTB) and low birth weight (LBW) are the leading causes of neonatal morbidity and mortality, but the effect of maternal height on these outcomes continues to be debated. Our objective was to determine the relationships between maternal height and PTB and LBW.

DATA SOURCES

Medline and EMBASE were searched from their inceptions.

STUDY SELECTION

Studies with a reference group that assessed the effect of maternal height on PTB (< 37 weeks) and LBW (< 2500 grams) in singletons were included.

DATA EXTRACTION

Data were extracted independently by two reviewers.

DATA SYNTHESIS

Fifty-six studies were included involving 333 505 women. In the cohort studies, the unadjusted risk of PTB in short-statured women was increased (relative risk [RR] 1.23; 95% CI 1.11 to 1.37), as was the unadjusted risk of LBW (RR 1.81; 95% CI 1.47 to 2.23), although not all of the studies with adjusted data found the same association. Maternal tall stature was not associated with PTB (unadjusted RR 0.97; 95% CI 0.82 to 1.14), although LBW was decreased (unadjusted RR 0.56; 95% CI 0.46 to 0.69), but not in the adjusted data.

CONCLUSION

From our complete systematic review and meta-analyses, to our knowledge the first in this area, we conclude that short-statured women have higher unadjusted risks of PTB and LBW and tall women have approximately one half the unadjusted risk of LBW of women of reference height.

The predictive value of first trimester fetal volume measurements, a prospective cohort study

OBJECTIVES

To determine if fetal volume (FV) measurements with three-dimensional ultrasound in the first trimester of pregnancy can detect the fetus at risk for preterm birth and/or low birth weight.

METHODS

In this prospective cohort study, 538 participants were included during the routine first trimester ultrasound examination. Volume measurements were performed with VOCAL (9°). Firstly, the relation between FV and gestational age for a set of participants with normal pregnancies (training set), was assessed using multiple linear regression analysis, which was then used to determine the expected normal values. Secondly, for a new set of participants with normal pregnancies and a set of participants with complicated pregnancies (preterm birth and/or low birth weight), i.e. the validation set, the observed fetal volumes (FVobserved) were compared with their expected normal values (FVexpected) and expressed as a percentage of the expected normal value. The difference in mean percentage was then assessed with independent-samples t-test. Finally, logistic regression analysis was applied to the validation set to analyze the ability to predict the pregnancy outcome with FV calculation.

RESULTS

Linear regression analysis of FV as a predictor of preterm birth and/or low birth weight did not result in significant (p=0.630 and 0.290, respectively) or clinical relevant results (standardized effect sizes of 0.061 and 0.179, respectively). The predicting quality was also very low (AUC=0.508 and 0.545 respectively).

CONCLUSIONS

Fetal volume measurements in the first trimester of pregnancy are not useful as a prognostic tool for predicting pregnancies of high risk for preterm birth or a low birth weight.

A prospective observational study of early fetal growth velocity and its association with birth weight, gestational age at delivery, preeclampsia, and perinatal mortality

OBJECTIVES

We aimed to measure early fetal growth velocity and to correlate this with the birth weight, gestational age at delivery, and with the incidence of adverse pregnancy outcomes specifically preeclampsia and perinatal mortality.

METHODS

A data based prospective observational study, wherein sonographic biometry data and specific pregnancy outcome related data were collected from pregnant women's records, starting soon after their first antenatal visit. Early fetal growth velocity was measured using BPD growth between 11 and 14 weeks scan and anomaly scan and standardizing this by Z scoring.

RESULTS

Out of 607 fetuses, 41 (6.7%) were slow growing, 531 (87.4%) normally growing, and 35 (5.7%) fast growing (Z scoring <10th(,) 10-90th, and >90th percentiles respectively). As fetal growth velocity increased, the mean birth weight decreased from 2958.7±388.9 (<10th centile), 2742.1±576.6 (10-90th centile), to 2339.3±729.4 (>90th centile); and gestational age at delivery decreased from 38.5±1.3 (<10th centile), 37.5±2.1 (10-90th centile), to 36.4±2.2 (>90th centile), and both these trends were statistically significant (p<0.001).Faster growing fetuses had a higher risk of preterm delivery(spontaneous+indicated) compared to other 2 groups [OR 4.42 (2.18,8.98)], and slower growing fetuses had a higher risk of postdated deliveries compared to other 2 groups [OR 3.042 (1.44, 6.45)].We found no significant association between early fetal growth velocity and incidence of small for gestational age at birth/low birth weight at term, preeclampsia, and perinatal mortality.

CONCLUSIONS

Early fetal growth velocity between first and second trimesters, may be one of the important factors influencing ultimate birthweight and gestational age at delivery.

Public Health Impact of Legal Termination of Pregnancy in the US: 40 Years Later

During the 40 years since the US Supreme Court decision in Doe versus Wade and Doe versus Bolton, restrictions on termination of pregnancy (TOP) were overturned nationwide. The use of TOP was much wider than predicted and a substantial fraction of reproductive age women in the U.S. have had one or more TOPs and that widespread uptake makes the downstream impact of any possible harms have broad public health implications. While short-term harms do not appear to be excessive, from a public perspective longer term harm is conceiving, and clearly more study of particular relevance concerns the associations of TOP with subsequent preterm birth and mental health problems. Clearly more research is needed to quantify the magnitude of risk and accurately inform women with the crisis of unintended pregnancy considering TOP. The current US data-gathering mechanisms are inadequate for this important task.

Correction of systematic bias in ultrasound dating in studies of small-for-gestational-age birth: an example from the Iowa Health in Pregnancy Study

The authors examined whether early ultrasound dating (≤20 weeks) of gestational age (GA) in small-for-gestational-age (SGA) fetuses may underestimate gestational duration and therefore the incidence of SGA birth. Within a population-based case-control study (May 2002-June 2005) of Iowa SGA births and preterm deliveries identified from birth records (n = 2,709), the authors illustrate a novel methodological approach with which to assess and correct for systematic underestimation of GA by early ultrasound in women with suspected SGA fetuses. After restricting the analysis to subjects with first-trimester prenatal care, a nonmissing date of the last menstrual period (LMP), and early ultrasound (n = 1,135), SGA subjects' ultrasound GA was 5.5 days less than their LMP GA, on average. Multivariable linear regression was conducted to determine the extent to which ultrasound GA predicted LMP dating and to correct for systematic misclassification that results after applying standard guidelines to adjudicate differences in these measures. In the unadjusted model, SGA subjects required a correction of +1.5 weeks to the ultrasound estimate. With adjustment for maternal age, smoking, and first-trimester vaginal bleeding, standard guidelines for adjudicating differences in ultrasound and LMP dating underestimated SGA birth by 12.9% and overestimated preterm delivery by 8.7%. This methodological approach can be applied by researchers using different study populations in similar research contexts.

Fetal volume measurements with three dimensional ultrasound in the first trimester of pregnancy, related to pregnancy outcome, a prospective cohort study

Background

First trimester growth restriction is associated with an increased risk of adverse birth outcomes (preterm birth, low birth weight and small for gestational age at birth). The differences between normal and abnormal growth in early pregnancy are small if the fetal size is measured by the crown-rump-length. Three-dimensional ultrasound volume measurements might give more information about fetal development than two-dimensional ultrasound measurements. Detection of the fetus with a small fetal volume might result in earlier detection of high risk pregnancies and a better selection of high risk pregnancies.

Methods

A prospective cohort study, performed at the Máxima Medical Centre, in Eindhoven-Veldhoven, the Netherlands. During the routine first trimester scan with nuchal translucency measurement 500 fetal volumes will be obtained. The gestational age is based on the first day of the last menstrual period in a regular menstrual cycle and by the crown-rump-length. The acquired datasets are collected and stored on a hard disk for offline processing and volume calculation. The investigator who performs the volume measurements is blinded for the results of the first trimester scan. The manual mode will be used to outline the Region Of Interest, the fetal head and rump, in all cross sections. The fetal volumes are calculated with a rotational step of 9°.

First, the relation between fetal volume and gestational age, for a set of participants with normal pregnancies (training set), will be assessed. This model will then be used to determine expected values of fetal volume for a normal pregnancy, which will be referred to as expected normal values. Secondly, for a new set of participants with normal pregnancies and a set of participants with complicated pregnancies (together defined as validation set), the observed fetal volumes (FV_observed) are compared with their expected normal values (FV_expected) and expressed as a percentage of the expected normal value. The mean difference in percentage error between the set of normal versus complicated pregnancies will then be compared using the independent-samples t-test. Finally, logistic regression analysis will be applied to the validation set of participants to analyze the possibility of predicting the pregnancy outcome after fetal volume calculation in the first trimester, using this percentage error.

Discussion

After this study it is clear whether FV measurement in the first trimester can detect high risk pregnancies. If it is possible to detect these pregnancies, more intensive follow up in these pregnancies might result in fewer complicated pregnancies and fewer fetal morbidities.

A new semi-automated method for fetal volume measurements with three-dimensional ultrasound: preliminary results

OBJECTIVE

Complications in pregnancy are suggested to be the result of intrauterine conditions in the first trimester of pregnancy. Three-dimensional ultrasound volume measurements might give more information, compared with two-dimensional measurements. Commonly available methods for volume measurements are not suited for daily practice. This is a report of preliminary results of a promising, more practical semi-automated method for volume calculations with three-dimensional ultrasound.

METHOD

Volume datasets of 16 objects (10.2-41.5 cm(3) ) were obtained. Euclidean shortening flow and Perona and Malik were used as image enhancement techniques. The image gradient was calculated. The points of interest were detected by the iso-intensity and the edge-detection technique. Volume measurements with Volume Computer-aided AnaLysis (VOCAL) are used as a reference. A volume dataset of a first trimester fetus was acquired to test this method in vivo.

RESULTS

The mathematical calculations with iso-intensity (Perona and Malik: average= -1.57 cm(3) , SD=4.05; and Euclidean shortening flow: average= -1.38 cm(3) , SD=2.47) showed results comparable with the VOCAL method (average= +1.28 cm(3) , SD=2.07). We also succeeded in detecting all voxels in the whole contour of a 12-week fetus.

CONCLUSION

Mathematical volume calculations are possible with the semi-automated method. We were able to apply this new method on a first trimester fetus. This new method is promising for future use in the daily practice.

Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses

BACKGROUND

Despite the current obesity epidemic, maternal underweight remains a common occurrence with potential adverse perinatal outcomes. Our objective was to determine the relationship between maternal underweight and preterm birth (PTB) and low birth weight (LBW) in singleton pregnancies in developing and developed countries.

METHODS

We followed the MOOSE consensus statement. We searched MEDLINE and EMBASE from their inceptions. We included studies that assessed the effect of maternal underweight compared with normal weight according to body mass index in singleton gestations on our two primary outcomes: PTB (<37 weeks) and LBW (<2500 g). Two assessors independently reviewed citations, extracted data and assessed quality.

RESULTS

A total of 78 studies were included involving 1 025 794 women. The overall risk of PTB was increased in the cohort studies of underweight women [adjusted relative risk (RR) 1.29, 95% confidence interval (CI) 1.15-1.46], as were the risks of spontaneous PTB (adjusted RR 1.32, 95% CI 1.10-1.57) and induced PTB (adjusted RR 1.21, 95% CI 1.07-1.36). Underweight women had an increased risk of an LBW infant (adjusted RR 1.64, 95% CI 1.38-1.94). In developed countries, underweight women had an increased risk of PTB (RR 1.22, 95% CI 1.15-1.30) but not in developing countries (RR 0.99, 95% CI 0.67-1.45). In both developed and developing countries, underweight women were at increased risk of having an LBW infant (RR 1.48, 95% CI 1.29-1.68, and RR 1.52, 95% CI 1.25-1.85, respectively).

CONCLUSIONS

In this systematic review and meta-analyses, we determined that singletons born to underweight women have higher risks of PTB (overall, spontaneous and induced) and LBW than those born to women with normal weight.

Antiretroviral therapy and preterm delivery-a pooled analysis of data from the United States and Europe

OBJECTIVE

 To investigate reported differences in the association between highly active antiretroviral therapy (HAART) in pregnancy and the risk of preterm delivery among HIV-infected women.

DESIGN

  Combined analysis of data from three observational studies.

SETTING

 USA and Europe.

POPULATION

  A total of 19, 585 singleton infants born to HIV-infected women, 1990-2006.

METHODS

  Data from the Pediatric Spectrum of HIV Disease project (PSD), a US monitoring study, the European Collaborative Study (ECS), a consented cohort study, and the National Study of HIV in Pregnancy and Childhood (NSHPC), the United Kingdom and Ireland surveillance study.

MAIN OUTCOME MEASURE

  Preterm delivery rate (<37 weeks of gestation).

RESULTS

  Compared with monotherapy, HAART was associated with increased preterm delivery risk in the ECS (adjusted odds ratio [AOR] 2.40, 95% CI 1.49-3.86) and NSHPC (AOR 1.43, 95% CI 1.10-1.86), but not in the PSD (AOR 0.92, 95% CI 0.67-1.26), after adjusting for relevant covariates. Because of heterogeneity, data were not pooled for this comparison, but heterogeneity disappeared when HAART was compared with dual therapy (P = 0.26). In a pooled analysis, HAART was associated with 1.5-fold increased odds of preterm delivery compared with dual therapy (95% CI 1.19-1.87, P=0.001), after adjusting for covariates.

CONCLUSIONS

  Heterogeneity in the association between HAART and preterm delivery was not explained by study design, adjustment for confounders or a standard analytical approach, but may have been the result of substantial differences in populations and data collected. The pooled analysis comparing HAART with dual therapy showed an increased risk of preterm delivery associated with HAART.

Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analyses

OBJECTIVE

To determine the relation between overweight and obesity in mothers and preterm birth and low birth weight in singleton pregnancies in developed and developing countries.

DESIGN

Systematic review and meta-analyses.

DATA SOURCES

Medline and Embase from their inceptions, and reference lists of identified articles.

STUDY SELECTION

Studies including a reference group of women with normal body mass index that assessed the effect of overweight and obesity on two primary outcomes: preterm birth (before 37 weeks) and low birth weight (<2500 g).

DATA EXTRACTION

Two assessors independently reviewed titles, abstracts, and full articles, extracted data using a piloted data collection form, and assessed quality.

DATA SYNTHESIS

84 studies (64 cohort and 20 case-control) were included, totalling 1 095 834 women. Although the overall risk of preterm birth was similar in overweight and obese women and women of normal weight, the risk of induced preterm birth was increased in overweight and obese women (relative risk 1.30, 95% confidence interval 1.23 to 1.37). Although overall the risk of having an infant of low birth weight was decreased in overweight and obese women (0.84, 0.75 to 0.95), the decrease was greater in developing countries than in developed countries (0.58, 0.47 to 0.71 v 0.90, 0.79 to 1.01). After accounting for publication bias, the apparent protective effect of overweight and obesity on low birth weight disappeared with the addition of imputed "missing" studies (0.95, 0.85 to 1.07), whereas the risk of preterm birth appeared significantly higher in overweight and obese women (1.24, 1.13 to 1.37).

CONCLUSIONS

Overweight and obese women have increased risks of preterm birth and induced preterm birth and, after accounting for publication bias, appeared to have increased risks of preterm birth overall. The beneficial effects of maternal overweight and obesity on low birth weight were greater in developing countries and disappeared after accounting for publication bias.

Large fetal size in early pregnancy associated with macrosomia

OBJECTIVE

To assess if fetal size at the time of ultrasound dating examination is associated with the risk of macrosomia and complications associated with macrosomia.

METHODS

This was a retrospective cohort study of 19 377 singleton pregnancies dated in gestational weeks 16-20 during the period 1998-2004 at Danderyd Hospital, Stockholm, Sweden. Obstetric outcome was assessed through linkage to the Swedish Medical Birth Register.

RESULTS

When fetuses were > or = 7 days larger than expected at dating, compared with the expected size according to last menstrual period, there was a 59% increase in the risk of birth weight > or = 4500 g and a 145% increase in the risk of birth weight > or = 5000 g (odds ratio (OR), 1.59; 95% CI, 1.12-2.24 and OR, 2.45; 95% CI, 1.22-4.90, respectively). For a birth weight of > or = 4000 g the risk estimate was 1.19 (95% CI, 0.96-1.47).

CONCLUSION

Fetuses that are larger than expected in the second trimester have an increased risk of macrosomia. This emphasizes that fetal size in early pregnancy is not only a function of gestational duration, but also of fetal growth. However, only a limited proportion of all infants born macrosomic can be identified as such at the time of ultrasound dating.

Dietary and clinical impacts of nausea and vomiting during pregnancy

BACKGROUND

Nutrition during pregnancy is important for the health of both mother and infant. Nausea and vomiting in pregnancy (NVP) may alter food intake but the dietary and clinical consequences of NVP are poorly understood. The present study aimed to identify the differences in dietary intakes and clinical characteristics of women with NVP compared with those without.

METHODS

Women with (n = 134) or without (n = 53) NVP were studied in each trimester of pregnancy. The babies were studied at birth, and at 1 and 6 months. The presence of nausea and vomiting was established by interviews using standard questions. Daily intakes of foods and nutrients were assessed from 3-day food diaries. Weight gain during pregnancy and weights and lengths of the infants at birth and at 1 and 6 months of age were recorded.

RESULTS

In the first trimester, intake of meat products and thus protein in women with NVP was lower both quantitatively (P = 0.007) and as a proportion of energy (16.4E% [interquartile range (IQR) 14.9-18.4]) compared to non-NVP [18.3E% (IQR 16.3-19.8), P = 0.003]. The proportional intakes of carbohydrates were higher in NVP subjects [50.1E% (IQR 46.7-53.6)] than in non-NVP [46.8E% (IQR 43.6-51.9), P = 0.008]. Dietary and total intakes of vitamin B(12), total intake of magnesium and dietary intake of zinc were lower in women with NVP. Changes in diet remained throughout pregnancy. Women with NVP had shorter pregnancies [39.9 (95% CI 39.6-40.1)] compared with those without [40.4 (95% CI 40.1-40.8) weeks, P = 0.018], but neither pregnancy weight gain nor infants' weight and length differed.

CONCLUSIONS

Nausea and vomiting in pregnancy modified dietary intake and has potential clinical impacts as suggested by the altered pregnancy duration. In view of the programming effect of early nutrition, these alterations may carry long-term health consequences.

Primiparity: An ‘intermediate’ risk group for spontaneous and medically indicated preterm birth

OBJECTIVE

Most women in their first pregnancy are at 'unknown' risk for preterm birth. We hypothesized that such women may be at an increased risk for preterm birth in comparison to those with a prior term birth.

METHODS

We used Missouri's maternally-linked data (1989-97), comprised of women delivering their first singleton live birth (N = 259 431) and women delivering their first two consecutive singleton live births (N = 154 810). We compared preterm birth (<37 weeks) rates among women with a previous term birth, women with no reproductive history (primiparous women), and in those with a previous preterm birth. Risks of spontaneous and medically indicated preterm birth were also examined after adjustments for confounders through multivariate log-binomial regression models.

RESULTS

Preterm birth rates were 8.1%, 9.6%, and 23.3% among women with a previous term birth, among primiparous women, and among those with a previous preterm birth, respectively. In comparison to women with a prior term birth, risks of spontaneous preterm birth among primiparous women and among women with a prior preterm birth were 1.1-fold (95% confidence interval (CI) 1.0, 1.2) and 2.5-fold (95% CI 2.4, 2.6) higher, respectively. These risks were higher for medically indicated preterm birth among both primiparous women (RR 1.3, 95% CI 1.2, 1.4) and those with a prior preterm birth (RR 3.2, 95% CI 3.0, 3.5) than for spontaneous preterm births.

CONCLUSIONS

Primiparous women are at increased risk of both medically indicated and spontaneous preterm birth. The findings suggest that studies on preterm birth should consider a risk assignment to include three groups: low-risk (prior term birth), intermediate risk (primiparity), and high-risk (prior preterm birth). This strategy will be informative for the identification of women with impending risk of delivering preterm, and complications associated with prematurity.

Early fetal size and growth as predictors of adverse outcome

OBJECTIVE

To evaluate the association between fetal size and growth between the first and second trimesters and subsequent adverse pregnancy outcome.

METHODS

A cohort was created of 7,642 singleton pregnancies cared for in three obstetric units associated with Copenhagen University. Data were obtained from ultrasound measurements at 11-14 weeks (crown-rump length, biparietal diameter) and 17-21 weeks (biparietal diameter). Fetal size was assessed by gestation-specific z scores, and fetal growth between the first and second trimester was calculated individually using conditional centiles. The main outcome measures were preterm delivery, smallness for gestational age, and perinatal death.

RESULTS

Slow growth of the biparietal diameter less than the 10th and less than the 2.5th conditional centiles between first and second trimesters occurred in 10.4% and 3.6% of the population, respectively. Biparietal diameter growth less than the 10th centile was associated with perinatal death before 34 weeks (risk 0.5% compared with 0.04%, odds ratio [OR] 16.0, confidence interval [CI] 2.9-88.7). Biparietal diameter growth less than the 2.5th centile was the best predictor of perinatal death at any gestation, with a positive likelihood ratio of 4.7 and an OR of 7.3 (CI 2.4-22.2). In contrast, the biparietal diameter, dated by crown-rump length, did not have an increased risk of perinatal death; however, there was a mildly increased risk of small for gestational age birth weight (less than the 10th customized centile) if the biparietal diameter was below the 10th centile in the first trimester (risk 17% compared with 12%, OR 1.5, CI 1.2-1.8) or in the second trimester (risk 15.8% compared with 12.4%, OR 1.3, CI 1.1-1.5).

CONCLUSION

Slow growth of the fetal biparietal diameter between the first and second trimesters of pregnancy is a strong predictor of perinatal death before 34 weeks.

Invited commentary: disaggregating preterm birth to determine etiology

Identifying the causes of preterm birth has been problematic, in part because of heterogeneous pathways leading to the same event, early delivery. If a risk factor affects only a subset of cases, then studies that address the aggregate outcome will generate diluted measures of association. McElrath et al. (Am J Epidemiol. 2008;168(9):980-989) examined an array of potential influences on very early preterm birth (<28 weeks' gestation) and divided cases on the basis of proximal causes. Through factor analysis, they found empirical support for dividing preterm cases into 2 groups: intrauterine inflammation (preterm labor, preterm membrane rupture, placental abruption, and cervical insufficiency) and abnormal placentation (preeclampsia and intrauterine growth restriction). Replication of this classification in less extreme preterm births is needed, requiring large numbers of preterm births that have been characterized in detail. Nonetheless, this division is worthy of study by using previously collected data to determine whether, in fact, stronger associations are found for these subsets than for preterm birth in the aggregate. Ultimately, the test of the approach is in improving our understanding of etiology, ideally generating stronger, more consistent associations with preterm birth subsets than have been found for preterm birth in the aggregate.

Fetal size in the second trimester is associated with the duration of pregnancy, small fetuses having longer pregnancies

Background

Conventionally, the pregnancy duration is accepted to be 280–282 days. Fetuses determined by ultrasound biometry to be small in early pregnancy, have an increased risk of premature birth. We speculate that the higher rate of preterm delivery in such small fetuses represents a pathological outcome not applicable to physiological pregnancies. Here we test the hypothesis that in low-risk pregnancies fetal growth (expressed by fetal size in the second trimester) is itself a determinant for pregnancy duration with the slower growing fetuses having a longer pregnancy.

Methods

We analysed duration of gestation data for 541 women who had a spontaneous delivery having previously been recruited to a cross-sectional study of 650 low-risk pregnancies. All had a regular menses and a known date of their last menstrual period (LMP). Subjects were examined using ultrasound to determine fetal head circumference (HC), abdominal circumference (AC) and femur length (FL) at 10–24 weeks of gestation. Length of the pregnancy was calculated from LMP, and birth weights were noted. The effect of fetal size at 10–24 weeks of gestation on pregnancy duration was assessed also when adjusting for the difference between LMP and ultrasound based fetal age.

Results

Small fetuses (z-score -2.5) at second trimester ultrasound scan had lower birth weights (p < 0.0001) and longer duration of pregnancy (p < 0.0001) than large fetuses (z-score +2.5): 289.6 days (95%CI 288.0 to 291.1) vs. 276.1 (95%CI 273.6 to 278.4) for HC, 289.0 days (95%CI 287.4 to 290.6) vs. 276.9 days (95%CI 274.4 to 279.2) for AC and 288.3 vs. 277.9 days (95%CI 275.6 to 280.1) for FL. Controlling for the difference between LMP and ultrasound dating (using HC measurement), the effect of fetal size on pregnancy length was reduced to half but was still present for AC and FL (comparing z-score -2.5 with +2.5, 286.6 vs. 280.2 days, p = 0.004, and 286.0 vs. 280.9, p = 0.008, respectively).

Conclusion

Fetal size in the second trimester is a determinant of birth weight and pregnancy duration, small fetuses having lower birth weights and longer pregnancies (up to 13 days compared with large fetuses). Our results support a concept of individually assigned pregnancy duration according to growth rates rather than imposing a standard of 280–282 days on all pregnancies.

Expected day of delivery from ultrasound dating versus last menstrual period--obstetric outcome when dates mismatch

OBJECTIVE

To analyse the association between fetal size at time of dating ultrasound and risk for preterm delivery and small-for-gestational-age (SGA) birth and to evaluate if timing of ultrasound, that is before 14 weeks of gestation or after 16 weeks affects this association.

DESIGN

Retrospective cohort study.

SETTING

Ultrasound departments of Ultragyn, Stockholm, Sweden.

POPULATION

A total of 28,776 singleton pregnancies dated between 1998 and 2004.

METHODS

Obstetric outcome was assessed through linkage of the cohort to the Swedish Medical Birth Register.

MAIN OUTCOME MEASURES

Risks of preterm delivery, low birthweight for gestational age, pre-eclampsia, asphyxia, respiratory distress, instrumental delivery, caesarean section, and postterm birth were calculated for the groups dated early and late.

RESULTS

When the expected date of delivery was postponed after ultrasound dating by 7 days or more, there was an increased risk for preterm delivery and pre-eclampsia in the late dating group (OR 1.49, 95% CI 1.27-1.73 and OR 1.27, 95% CI 1.02-1.60, respectively) but not in the early dating group. In both dating groups, there was an increased risk for SGA birth (OR 1.77, 95% CI 1.13-2.78 and OR 2.09, 95% CI 1.59-2.73, respectively) There was no increased risk for any of the other diagnoses.

CONCLUSION

Our study gives further support to the notion that intrauterine growth restriction may be present as early as the first trimester. Accordingly, our study also suggests that surveillance of pregnancies with postponed estimated date of delivery may provide means for increased detection of fetal growth restriction.

Fatores de risco associados ao nascimento de recém-nascidos de muito baixo peso em uma população de baixa renda

Identificar os fatores de risco associados ao nascimento de recém-nascidos de muito baixo peso no Hospital Geral de Caxias do Sul, Rio Grande do Sul, Brasil. Estudo de caso-controle, abrangendo 200 recém-nascidos com peso entre 500 e 1.499g (casos) e 400 recém-nascidos com peso entre 3.000 e 3.999g (controles). Incluídos recém-nascidos de gestação única, cujas mães não realizaram pré-natal ou o fizeram na rede pública. A variável dependente foi o peso de nascimento e as variáveis independentes foram as sócio-econômicas, educacionais, gestacionais e do parto. Utilizou-se a análise univariada e multivariada, com nível de significância de 5%. A mortalidade dos recém-nascidos de muito baixo peso foi de 32,5%. O limite de viabilidade dos recém-nascidos foi 600g de peso e 26 semanas de idade gestacional. As variáveis relacionadas com o nascimento prematuro foram: idade materna > 35 anos (p = 0,01), ausência de pré-natal (p < 0,0001), doenças na gestação (p = 0,03), hipertensão materna (p = 0,007), internação na gestação (p < 0,0001) e filho anterior de baixo peso ao nascer (p < 0,0001). Muitos nascimentos prematuros ocorreram por causas evitáveis.

The research implications of the selection of a gestational age estimation method

There are three primary methods of gestational age estimation: dating based on last menstrual period (LMP), ultrasound-based dating and neonatal estimates. We review the strengths and limitations of each method as well as their implications for research. Dating based on LMP is a simple, low-cost method of estimating gestational age. Limitations associated with the use of menstrual-based dating include reporting problems such as uncertainty regarding the LMP date, possibly due to bleeding not associated with menses, as well as concerns about the incidence of delayed ovulation, which can result in invalid estimates of gestation, even for women with certain LMP dates. Given that most women in the US have at least one ultrasound during pregnancy, it is becoming increasingly common for clinicians to verify menstrual dates using early ultrasound. To calculate gestational age with the use of ultrasound, fetal measurements are compared with a gestational age-specific reference. The primary limitation of this method is the fact that the gestational age estimates of symmetrically large or small fetuses will be biased. Further, given that ultrasound references were developed using pregnancies that were dated according to reliable LMP dates, they are potentially biased in the same direction as dates calculated according to LMP. Neonatal estimates of gestational age have been shown to be the least precise dating method. To highlight the research implications of the choice of a gestational dating method, we used data from the Routine Antenatal Diagnostic Imaging with Ultrasound Study to identify risk factors for post-term delivery. Risk factors for post-term delivery are shown to vary according to the choice of a gestational dating method, suggesting that some findings are an artefact of the choice of a method rather than evidence of causality.

Smoking during pregnancy according to obstetric complications and parity: results of the EUROPOP study

This study aimed to analyse the relationship between smoking and preterm birth (22-36 weeks) according to the main obstetric complications leading to the preterm birth, both overall and by parity. The EUROPOP study is a case-control study carried out between 1994 and 1997; 3,787 preterm and 5,602 full-term births were included, from maternity units in 10 countries, using the same protocol. Social, demographic and medical information was collected after delivery, from obstetric records and interviews with the mothers. Cases were classified according to the main obstetric complication (hypertension, haemorrhage, preterm premature rupture of membranes (PPROM), idiopathic spontaneous preterm labour, intrauterine growth retardation, all other causes). Multiple logistic regression analysis was used to control for confounders. Twenty four percent of cases and 20% of controls were smokers. Smoking during pregnancy, heavy smoking (>or=10 cigarettes per day) in particular, was a risk factor for preterm birth (aOR = 1.39, 95% CI:1.20-1.60). Smoking increased the risk of preterm delivery due to all obstetric complications other than hypertension. For these complications, the risk of preterm delivery associated with smoking was higher for multiparae (aOR = 1.46, 95% CI:1.24-1.71) than for primiparae (aOR = 1.18, 95% CI:1.00-1.38). In conclusion, smoking during pregnancy increases the risk of preterm birth among women with all obstetric complications except hypertension. This association is stronger in multiparae than in primiparae and the risk is higher for heavy smokers.

Antiretroviral therapy and premature delivery in diagnosed HIV-infected women in the United Kingdom and Ireland

OBJECTIVE

To explore the association between antiretroviral therapy in pregnancy and premature delivery, birthweight, stillbirth and neonatal mortality, in pregnancies in HIV-infected women delivering between 1990 and 2005.

DESIGN

Pregnancies in women with diagnosed HIV infection in the UK and Ireland are notified to the National Study of HIV in Pregnancy and Childhood (NSHPC) through a well-established surveillance scheme.

RESULTS

The prematurity rate (< 37 weeks gestation) was higher in women on highly active antiretroviral therapy (HAART) (14.1%, 476/3384) than in women on mono/dual therapy (10.1%, 107/1061), even after adjusting for ethnicity, maternal age, clinical status and injecting drug use as the source of HIV acquisition [adjusted odds ratio (AOR) = 1.51, 95% confidence interval (CI), 1.19-1.93; P = 0.001]. Delivery at < 35 weeks was even more strongly associated with HAART (AOR = 2.34; 95% CI, 1.64-3.37; P < 0.001). The effect was the same whether or not HAART included a protease inhibitor. In comparison with exposure to mono/dual therapy, exposure to HAART was associated with lower birthweight standardized for gestational age (P < 0.001), and an increased risk of stillbirth (AOR = 2.27; 95% CI, 0.96-5.41; P = 0.063).

CONCLUSIONS

These findings, based on comprehensive population surveillance, demonstrate an increased risk of prematurity associated with HAART, and a possible association with other perinatal outcomes, including stillbirth and birthweight. Although the beneficial effects of antiretroviral therapy on mother-to-child transmission are indisputable, monitoring antiretroviral therapy in pregnancy remains a priority.

Fetal growth in early pregnancy and risk of delivering low birth weight infant: prospective cohort study

OBJECTIVE

To determine if first trimester fetal growth is associated with birth weight, duration of pregnancy, and the risk of delivering a small for gestational age infant.

DESIGN

Prospective cohort study of 38 033 pregnancies between 1999 and 2003.

SETTING

15 centres representing major regions of the United States.

PARTICIPANTS

976 women from the original cohort who conceived as the result of assisted reproductive technology, had a first trimester ultrasound measurement of fetal crown-rump length, and delivered live singleton infants without evidence of chromosomal or congenital abnormalities. First trimester growth was expressed as the difference between the observed and expected size of the fetus, expressed as equivalence to days of gestational age.

MAIN OUTCOME MEASURES

Birth weight, duration of pregnancy, and risk of delivering a small for gestational age infant.

RESULTS

For each one day increase in the observed size of the fetus, birth weight increased by 28.2 (95% confidence interval 14.6 to 41.2) g. The association was substantially attenuated by adjustment for duration of pregnancy (adjusted coefficient 17.1 (6.6 to 27.5) g). Further adjustments for maternal characteristics and complications of pregnancy did not have a significant effect. The risk of delivering a small for gestational age infant decreased with increasing size in the first trimester (odds ratio for a one day increase 0.87, 0.81 to 0.94). The association was not materially affected by adjustment for maternal characteristics or complications of pregnancy.

CONCLUSION

Variation in birth weight may be determined, at least in part, by fetal growth in the first 12 weeks after conception through effects on timing of delivery and fetal growth velocity.

Courbes de poids à la naissance: une revue de la littérature

There are many birthweight reference curves in the literature. This study reviews birthweight curves that are commonly used in France as well as references that provide birthweight by sex. The 19 curves selected for review were published between 1971 and 2001 using samples of between 300 to 3 million newborns in Europe, Australia and North America. Our objective was to summarize their main characteristics and to provide guidelines for analysis by explaining which factors are responsible for differences between curves, and discussing the methods used to construct them. The characteristics of the population must be taken into account and study samples must be recent and representative. The sample size must be sufficient to ensure stable estimates for premature infants. It is preferable to use different curves for boys and girls because sex is a key determinant of birth weight. The choice of appropriate birth weight reference remains difficult in some countries, in France particularly, and the use of individual customised birth weight curves provides an interesting alternative.

Smoking during pregnancy and preterm birth according to obstetric history: French national perinatal surveys

The relation between smoking and preterm delivery is not totally known. Our aim was to determine whether smoking during pregnancy was associated with preterm birth among women at different risk according to their obstetric history. The study was based on data from the 1998 French national perinatal survey. Of the 13073 singleton live births, 4.7% were preterm; 15% of the pregnant women were moderate (one to nine cigarettes per day) and 10% heavy smokers (at least 10 cigarettes per day). Smoking heavily was related to preterm birth (crude odds ratio [OR] = 1.35, 95% confidence interval [95% CI]: [1.04, 1.74]). Multivariable logistic regression showed a relation between smoking and preterm birth among multiparae without previous adverse pregnancy outcomes; the associated adjusted ORs (AORs) were 1.25 [95% CI 0.83, 1.87] among moderate smokers and 1.46 [95% CI 0.98, 2.20] among heavy smokers. The corresponding AORs were 0.69 [95% CI 0.46, 1.05]) and 0.96 [95% CI 0.59, 1.56] for primiparae and 1.11 [95% CI 0.63, 1.93] and 0.50 [95% CI 0.25, 0.98] for multiparae with previous adverse pregnancy outcomes. Our study showed a relation between heavy smoking during pregnancy and preterm birth mostly for women with low obstetric risk.

Prematurity and fetal growth restriction

Assessment of the growth status of the fetus and neonate is an essential component of perinatal care. It requires a distinction to be made between physiological and pathological factors, and the prediction of the optimal growth that a baby can achieve in a normal, uncomplicated pregnancy. Such an individually customised standard can now be easily calculated by computer: it needs to be accurately dated, individually adjusted for physiological characteristics, exclude pathological factors such as smoking, and be based on a fetal weight trajectory derived from normal term pregnancies. Application of a customised standard to calculate the growth status of preterm babies gives us freshly insights into the causes of prematurity. Fetal growth restriction is seen as a strongly associated factor, which is often present before the onset of spontaneous preterm labour. This raises the question whether, in many instances, the initiation of parturition should be seen as a fetal adaptive response aimed at escaping an unfavourable intrauterine environment. These concepts have implications for the understanding of the pathophysiology of preterm labour, as well as its clinical management.

The complex relationship between smoking in pregnancy and very preterm delivery. Results of the Epipage study

OBJECTIVE

To assess the relationship between cigarette smoking during pregnancy and very preterm births, according to the main mechanisms of preterm birth.

DESIGN

Case-control study (the French Epipage study).

SETTING

Regionally defined population of births in France.

POPULATION

Eight hundred and sixty-four very preterm live-born singletons (between 27 and 32 completed weeks of gestation) and 567 unmatched full-term controls.

METHODS

Data from the French Epipage study were analysed using a polytomous logistic regression model to control for social and demographic characteristics, pre-pregnancy body mass index and obstetric history. The main mechanisms of preterm delivery were classified as gestational hypertension, antepartum haemorrhage, premature rupture of membranes, spontaneous preterm labour and other miscellaneous mechanisms.

MAIN OUTCOME MEASURES

Odds ratios for very preterm birth for low to moderate (1-9 cigarettes/day) and heavy (>/=10 cigarettes/day) maternal smoking in pregnancy, estimated according to the main mechanisms leading to preterm birth.

RESULTS

Smokers were more likely to give birth to very preterm infants than non-smokers [adjusted odds ratio (aOR) 1.7, 95% confidence interval (CI) 1.3-2.2]. Heavy smoking significantly reduced the risk of very preterm birth due to gestational hypertension (aOR 0.5, 95% CI 0.3-1.0), whereas both low to moderate and heavy smoking increased the risk of very preterm birth due to all other mechanisms (aOR between 1.6 and 2.8).

CONCLUSION

These data from the Epipage study show that maternal smoking during pregnancy is a risk factor for very preterm birth. The impact of maternal smoking on very preterm birth appears to be complex: it lowers the risk of very preterm birth due to gestational hypertension, but increases the risk of very preterm birth due to other mechanisms. These findings might explain why maternal smoking is more closely related to preterm birth among multiparous women than among nulliparous women.

Adverse obstetric outcome in fetuses that are smaller than expected at second trimester routine ultrasound examination

BACKGROUND

Adverse obstetric outcome in fetuses that are smaller than expected at second trimester routine ultrasound examination.

AIM

To assess the obstetric outcome when the interval between the estimated date of delivery by last menstrual period and the estimated date of delivery by second trimester ultrasound exceeds 14 days.

MATERIALS AND METHODS

Population-based prospective cohort study. Included were all women (n = 16 302) with a singleton pregnancy, in one Norwegian county from 1989 to 1999, with a reliable menstrual history and whose second trimester ultrasound examination was conclusive with a 35-60-mm biparietal diameter.

RESULTS

Adverse outcome was defined as preterm birth (< 37 weeks), perinatal death, low birthweight (< 2500 g) and small-for-gestational age (< 2 standard deviation). The risk for perinatal death (odds ratio = 2.3), preterm birth (odds ratio = 1.7), low birth weight (odds ratio = 1.5), and small-for-gestational age (odds ratio = 1.5) was highly significantly increased in deliveries where the discrepancy between the two terms was more than 14 days. The increased risk is not explained by differences in parity, maternal age, smoking, fetal malformations, or use of oral contraceptives before pregnancy.

CONCLUSION

Fetuses that are smaller than expected at the mid-second trimester ultrasound corresponding to a discrepancy of more than 14 days have an increased risk for adverse obstetric outcome.

The epidemiology of preterm labor

There are many factors that are associated with preterm labor and delivery. These include maternal conditions such as medical illness, anemia and uterine malformation. They may be related to past events such as prior obstetric complication, previous preterm labor, cervical surgery or induced abortion. They may be intrinsic to the current pregnancy, such as reproductive tract infection, multifetal gestation, maternal age, short interpregnancy interval or prolonged menstrual conception interval. Maternal behaviors such as smoking and substance abuse can be risk factors for a short gestation. Demographic variables such as race, employment and socioeconomic status can also be associated with preterm labor. This article briefly reviews these subjects.

Role of structural birth defects in preterm delivery

The proportion of preterm births associated with structural birth defects has not been adequately quantified. We explored the proportion of preterm infants with structural birth defects diagnosed in the first year of life, as well as the specific phenotypes of birth defects occurring among preterm infants. The data used were from the California Birth Defects Monitoring Program, a population-based registry, as well as data from California vital records corresponding to births and fetal deaths in the period 1984-96. The prevalence of structural birth defects exceeded 8% among deliveries with gestational ages < or = 30 weeks, and prevalence decreased to 2% as gestational age increased to > or = 37 weeks gestation. The decreasing prevalence pattern with increasing gestational age was observed for a variety of anatomically defined birth defect groups suggesting that certain birth defects were not the sole contributors to the elevated prevalences among preterm births. Decreasing prevalence with increasing gestational age was also observed across strata of maternal race/ethnicities, ages, infant's sex and each year studied. These data indicate that structural birth defects may contribute significantly to the proportion of infants who are delivered before 37 weeks gestation.