Optimal growth modeling

Sonographic growth curves versus neonatal birthweight growth curves for the identification of fetal growth restriction

OBJECTIVE

Fetal growth restriction is suspected when the estimated fetal weight is <10th percentile for gestational age. Using a regional sonographic estimated fetal weight growth curve to diagnose fetal growth restriction has no known benefits; however, the traditional approach of using birthweight curves is misleading, since a large proportion of preterm births arise from pathological pregnancies. Our aim was to compare the diagnostic accuracies of sonographic versus birthweight curves in diagnosing fetal growth restriction. Our secondary aim was to compare maternal, fetal and neonatal outcome based on these two approaches.

METHODS

Retrospective study based on computerized medical records. Included were women with a singleton pregnancy, that underwent fetal biometry between 24 and 36.6 weeks' gestation (January 2010-February 2016) and delivered in our center. Each pregnancy was assigned to one of three groups based on the earliest sonographic estimated fetal weight performed: G1-Appropriate for gestational age, G2-fetal growth restriction based on sonographic but not birthweight curves; or G3-fetal growth restriction based on birthweight growth curves. Demographics, obstetric characteristics, ultrasound data, and neonatal data were retrieved and compared between groups. Primary outcome: rate of small for gestational age neonates in each group. Secondary outcomes were various adverse maternal and neonatal outcomes.

RESULTS

Six thousand and five pregnancies met inclusion criteria. Of these 5386 (89.6%) were categorized as G1, 300 (5%) as G2 and 319 (5.3%) as G3. The rate of small for gestational age neonates differed significantly between groups: G1 9.2%, G2 39.7% and G3 70%. Multivariable logistic regression modeling reiterated these rates: the odds ratios for small for gestational age were 6.47 [95% CI 4.99-8.40] and 23.99 [95% CI 18.26-31.51] for G2 and G3 respectively. Prediction of small for gestational age based on sonographic EFW curves increased the sensitivity for detection of SGA from 26% to 41% with a slight decrease in specificity from 98% to 95%, and a decrease of the positive likelihood ratio from 18.4 to 7.7, however there was no significant change in the overall test accurcy; 88.5% to 87.1%. Secondary outcomes also differed between groups: G2 and G3 had similar rates of maternal and neonatal morbidities and most parameters were higher than G1. G2 and G3 showed lower mean gestational age at delivery (36.2 weeks and 35.9 weeks vs.37.8; p < .0001), and higher rates of preterm delivery (40% and 51.7% vs. 21.5%; p < .001), as well as higher rates of intrauterine fetal demise 3% in G2, 6.9% in G3 and 0.9% in G1, p < .0001.

CONCLUSION

Pregnancies that are currently managed as appropriate for gestational age based on birthweight curves, but classified as growth restricted when prenatal sonographic curves are used, are associated with higher rates of small for gestational age and poor perinatal outcomes, at rates comparable to pregnancies that are classified as growth restricted based on birthweight curves. Furthermore, applying sonographic curves increases the sensitivity for detection of small for gestational age neonates. Consequently, consideration should be given to the use of sonographic biometry curves for defining fetal growth restriction.

Preventing term stillbirth: benefits and limitations of using fetal growth reference charts

PURPOSE OF REVIEW

This review examines the variation in clinical practice with regards to ultrasound estimation of fetal weight, as well as calculation of fetal weight centiles.

RECENT FINDINGS

Placental dysfunction is associated with fetal smallness from intrauterine malnutrition as well as fetal disability and even stillbirth from hypoxemia. Although estimating fetal weight can be done accurately, the issue of which fetal weight centile chart should be used continues to be a contentious topic. The arguments against local fetal growth charts based on national borders and customization for variables known to be associated with disease are substantial. As for other human diseases such as hypertension and diabetes, there is a rationale for the use of an international fetal growth reference standard. Irrespective of the choice of fetal growth reference standard, a significant limitation of small for gestational age (SGA) detection programs to prevent stillbirth is that the majority of stillborn infants at term were not SGA at the time of demise.

SUMMARY

Placental dysfunction can present with SGA from malnutrition and/or stillbirth from hypoxemia depending on the gestational age of onset. Emerging data show that at term, fetal Doppler arterial redistribution is associated more strongly with perinatal death than fetal size. Properly conducted trials of the role for maternal characteristics, fetal size, placental biomarkers, and Doppler assessing fetal well-being are required urgently.

New Australian birthweight centiles

OBJECTIVES

To prepare more accurate population-based Australian birthweight centile charts by using the most recent population data available and by excluding pre-term deliveries by obstetric intervention of small for gestational age babies.

DESIGN

Population-based retrospective observational study.

SETTING

Australian Institute of Health and Welfare National Perinatal Data Collection.

PARTICIPANTS

All singleton births in Australia of 23-42 completed weeks' gestation and with spontaneous onset of labour, 2004-2013. Births initiated by obstetric intervention were excluded to minimise the influence of decisions to deliver small for gestational age babies before term.

MAIN OUTCOME MEASURES

Birthweight centile curves, by gestational age and sex.

RESULTS

Gestational age, birthweight, sex, and labour onset data were available for 2 807 051 singleton live births; onset of labour was spontaneous for 1 582 137 births (56.4%). At pre-term gestational ages, the 10th centile was higher than the corresponding centile in previous Australian birthweight charts based upon all births.

CONCLUSION

Current birthweight centile charts probably underestimate the incidence of intra-uterine growth restriction because obstetric interventions for delivering pre-term small for gestational age babies depress the curves at earlier gestational ages. Our curves circumvent this problem by excluding intervention-initiated births; they also incorporate more recent population data. These updated centile curves could facilitate more accurate diagnosis of small for gestational age babies in Australia.

Implementing the INTERGROWTH-21st gestational dating and fetal and newborn growth standards in peri-urban Nairobi, Kenya: Provider experiences, uptake and clinical decision-making

BACKGROUND

Perinatal and newborn complications are major risk factors for unfavorable fetal and neonatal outcomes. Gestational dating and growth monitoring can be instrumental in the identification and management of high-risk pregnancies and births. The INTERGROWTH-21st Project developed the first global standards for gestational dating and fetal and newborn growth monitoring, supplying a toolkit for clinicians. This study aimed to assess the feasibility and acceptability of the first known implementation study of these standards in a low resource setting.

METHODS

The study was performed in two 12-month phases from March 2016 to March 2018 at Jacaranda Health, a private maternity hospital in peri-urban Nairobi, Kenya. In-depth interviews, focus group discussions and a provider survey were utilized to evaluate providers' experiences during implementation. Client chart data, for pregnant women attending antenatal care and/or delivering at Jacaranda Health along with their newborns, were captured to assess uptake and effect of the standards on clinical decision-making.

RESULTS

Facility-level support and provider buy-in proved to be critical factors driving the success of implementing the standards. However, additional support was needed to strengthen capacity to conduct and interpret ultrasounds and maintain motivation among providers. We observed a significant increase in the uptake of obstetric ultrasounds, particularly gestational dating, during the implementation of the standards. Although no significant changes were detected in the identification of high-risk pregnancies, referrals and deliveries by Cesarean section during implementation, we did observe a significant reduction in inductions for post-date. No significant barriers were reported regarding the use of the newborn standards. Over 80% of providers advocated for the standards to remain in place with some enhancements related mainly to training, advocacy and procurement.

CONCLUSIONS

The findings are timely with increasing global adoption of the standards and the challenging and multi-faceted nature of translating new, evidence-based guidelines into routine clinical practice.

Effect of maternal age, height, BMI and ethnicity on birth weight: an Italian multicenter study

AIM

To assess the effect of maternal age, height, early pregnancy body mass index (BMI) and ethnicity on birth weight.

SUBJECTS AND METHODS

A cross-sectional study was conducted on more than 42,000 newborns. Ethnicity was defined by maternal country of birth or, when missing (<0.6% of records), by citizenship. The effect of maternal characteristics on birth weight was evaluated with general linear models.

RESULTS

Maternal height and BMI, although not age, significantly affected birth weight. Among Italian babies, 4.7% of newborns were classified as appropriate-for-gestational age (AGA) (birth weight between the 10th and the 90th centile) according to the country-specific Italian Neonatal Study (INeS) charts and were re-classified as either large-(LGA) (birth weight >90th centile) or small-(SGA) (birth weight <10th centile) for gestational age (GA) after adjustment for maternal characteristics. On the contrary, 1.6% of Italian newborns were classified as SGA or LGA according to the INeS charts and re-classified as AGA after adjustment. Maternal ethnicity had a significant impact on birth weight. Specifically, babies born to Senegalese mothers were the lightest, whilst babies born to Chinese mothers were the heaviest.

CONCLUSIONS

Maternal height and early pregnancy BMI, should be considered in the evaluation of birth weight. The effect of ethnicity suggests the appropriateness of ethnic-specific charts. Further studies are necessary to determine if changes in birth weight classification, may translate into improved detection of subjects at risk of adverse outcomes.

Customized vs population-based growth charts to identify neonates at risk of adverse outcome: systematic review and Bayesian meta-analysis of observational studies

OBJECTIVE

To compare the effectiveness of customized vs population-based growth charts for the prediction of adverse pregnancy outcomes.

METHODS

MEDLINE, ClinicalTrials.gov and The Cochrane Library were searched up to 31 May 2016 to identify interventional and observational studies comparing adverse outcomes among large- (LGA) and small- (SGA) for-gestational-age neonates, when classified according to customized vs population-based growth charts. Perinatal mortality and admission to the neonatal intensive care unit (NICU) of both SGA and LGA neonates, intrauterine fetal demise (IUFD) and neonatal mortality of SGA neonates, and neonatal shoulder dystocia and hypoglycemia as well as maternal third- and fourth-degree perineal lacerations in LGA pregnancies were evaluated.

RESULTS

The electronic search identified 237 records that were examined based on title and abstract, of which 27 full-text articles were examined for eligibility. After excluding seven articles, 20 observational studies were included in a Bayesian meta-analysis. Neonates classified as SGA according to customized growth charts had higher risks of IUFD (odds ratio (OR), 7.8 (95% CI, 4.2-12.3)), neonatal death (OR, 3.5 (95% CI, 1.1-8.0)), perinatal death (OR, 5.8 (95% CI, 3.8-7.8)) and NICU admission (OR, 3.6 (95% CI, 2.0-5.5)) than did non-SGA cases. Neonates classified as SGA according to population-based growth charts also had increased risk for adverse outcomes, albeit the point estimates of the pooled ORs were smaller: IUFD (OR, 3.3 (95% CI, 1.9-5.0)), neonatal death (OR, 2.9 (95% CI, 1.2-4.5)), perinatal death (OR, 4.0 (95% CI, 2.8-5.1)) and NICU admission (OR, 2.4 (95% CI, 1.7-3.2)). For LGA vs non-LGA, there were no differences in pooled ORs for perinatal death, NICU admission, hypoglycemia and maternal third- and fourth-degree perineal lacerations when classified according to either the customized or the population-based approach. In contrast, both approaches indicated that LGA neonates are at increased risk for shoulder dystocia than are non-LGA ones (OR, 7.4 (95% CI, 4.9-9.8) using customized charts; OR, 8.0 (95% CI, 5.3-10.1) using population-based charts).

CONCLUSIONS

Both customized and population-based growth charts can identify SGA neonates at risk for adverse outcomes. Although the point estimates of the pooled ORs may differ for some outcomes, the overlapping CIs and lack of direct comparisons prevent conclusions from being drawn on the superiority of one method. Future clinical trials should compare directly the two approaches in the management of fetuses of abnormal size. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Indonesian local fetal-weight standard: a better predictive ability for low Apgar score of SGA neonates

Background: Accurate assessment of fetal growth is one of crucial components of antenatal care. A generic reference for fetal-weight and birthweight percentiles that can be easily adapted to local populations have been developed by Mikolajczyk and colleagues. This study aimed to validate our own local percentile standard by evaluating the odds ratio (OR) of low 1st and 5th minute Apgar score for small-for-gestational age (SGA) versus those not SGA.Methods: We used the generic reference tools for fetal-weight and birthweight percentiles developed by Mikolajczyk and colleagues to create our own local standard and then defined the SGA neonates. For validation, we used the database of singleton live deliveries (2,139 birth) during January 1st to December 31st 2013 in Cipto Mangunkusumo Hospital, Jakarta, Indonesia. We compared our reference with that of Hadlock and colleagues. For every reference, the OR of Apgar score <7 at 1st and 5th minutes for infants who were SGA versus those not estimated with bivariate and multivariate analyses.Results: SGA found in 35% (748/2,139) and 13% (278/2,139) of neonates using the definition derived from Indonesian standard and Hadlock’s. OR of Apgar score <7 at 1st and 5th minutes were 3.45 (95% CI=2.56–4.65) and 3.05 (95% CI=1.92–4.83) for the Indonesian local fetal-weight standard compared with respectively 2.14 (95% CI=1.65–2.76) and 1.83 (95% CI=1.21–2.77) for Hadlock and collegues’ reference.Conclusion: Indonesian local fetal-weight standard has a better ability to predict low 1st and 5th minutes Apgar scores of SGA neonates than has the Hadlock and collegues’ reference.

Early Life Events Predict Adult Testicular Function; Data Derived From the Western Australian (Raine) Birth Cohort

CONTEXT

The impact of early life events on testicular function in adulthood is not well understood.

OBJECTIVE

To study the early influences of fetal growth, exposures to cigarette smoke in utero and cord blood estrogens, and the influences of growth and adiposity in childhood through adolescence; on testicular function in adulthood.

DESIGN

Male members of the Western Australian Pregnancy Cohort (Raine) were contacted at 20-22 years of age. Of 913 contacted, 423 (56%) agreed to participate; 404 underwent a testicular ultrasound, 365 provided a semen sample, and reproductive hormones were measured (384). Fetal growth measurements (n = 137), umbilical cord estrogen concentrations (n = 128), cord testosterone (T) (n = 125), and child-adulthood growth charts (n = 395) were available.

RESULTS

Median sperm output for the 18.6% of men exposed in utero to smoking was lower than nonexposed (82.4 × 10(6) vs 123.1 × 10(6); P = .029). Sperm output in adulthood was inversely correlated with cord serum estradiol (P = .019) and estrone (P = .018). The sperm output of men whose cord blood estradiol and estrone were less than 50th percentile vs more than 50th percentile was 191.1 × 10(6) vs 100.5 × 10(6) (P = .002) and 190.0 × 10(6) vs 106.0 × 10(6) (P = .012), respectively. Men with favorable fetal growth patterns in utero were less likely to have total motile sperm counts within the lowest quartile (P = .011), and men born prematurely had reduced serum T levels in adulthood (13.4 vs 16.6nmol/L, P = .024). Consistent height above the 50th percentile for age through childhood was associated with larger adult mean testicular volume (P < .001). Optimal body mass index trajectory through childhood and adolescence was associated with larger testicular volume (P = .009) and higher serum inhibin B (P = .010) and T (P = .003) in adulthood.

CONCLUSIONS

Exposures to maternal smoking and higher cord blood estrogens at delivery were associated with a reduced sperm output in adulthood. Optimal adult testicular function depends on being born at or above average weight, and maintaining optimal growth and adiposity into adulthood.

Differences in birthweight outcomes: a longitudinal study based on siblings

Objectives: We investigate the differences in birthweight between first- and second-borns, evaluating the impact of changes in pregnancy (e.g., gestational age), demographic (e.g., age), and social (e.g., education level, marital status) maternal characteristics. Data and Methods: All analyses are performed on data collected in Umbria (Italy) taking into account a set of 792 women who delivered twice from 2005 to 2008. Firstly, we use a univariate paired t-test for the comparison between weights of first- and second-borns; Secondly, we use linear and nonlinear regression approaches in order to: (i) evaluate the effect of demographic and social maternal characteristics and (ii) predict the odds-ratio of low and high birthweight infants, respectively. Results: We find that the birthweight of second-borns is significantly higher than that of first-borns. Statistically significant effects are related with a longer gestational age, an increased number of visits during the pregnancy, and the gender of infants. On the other hand, we do not observe any significant effect related with mother’s age and with other characteristics of interest.

Size at birth by gestational age and hospital mortality in very preterm infants: results of the area-based ACTION project

BACKGROUND

Size at birth is an important predictor of neonatal outcomes, but there are inconsistencies on the definitions and optimal cut-offs.

AIMS

The aim of this study is to compute birth size percentiles for Italian very preterm singleton infants and assess relationship with hospital mortality.

STUDY DESIGN

Prospective area-based cohort study.

SUBJECTS

All singleton Italian infants with gestational age 22-31 weeks admitted to neonatal care in 6 Italian regions (Friuli Venezia-Giulia, Lombardia, Marche, Tuscany, Lazio and Calabria) (n. 1605).

OUTCOME MEASURE

Hospital mortality.

METHODS

Anthropometric reference charts were derived, separately for males and females, using the lambda (λ) mu (μ) and sigma (σ) method (LMS). Logistic regression analysis was used to estimate mortality rates by gestational age and birth weight centile class, adjusting for sex, congenital anomalies and region.

RESULTS

At any gestational age, mortality decreased as birth weight centile increased, with lowest values observed between the 50th and the 89th centiles interval. Using the 75th-89th centile class as reference, adjusted mortality odds ratios were 7.94 (95% CI 4.18-15.08) below 10th centile; 3.04 (95% CI 1.63-5.65) between the 10th and 24th; 1.96 (95% CI 1.07-3.62) between the 25th and the 49th; 1.25 (95% CI 0.68-2.30) between the 50(h) and the 74th; and 2.07 (95% CI 1.01-4.25) at the 90th and above.

CONCLUSIONS

Compared to the reference, we found significantly increasing adjusted risk of death up to the 49th centile, challenging the usual 10th centile criterion as risk indicator. Continuous measures such as the birthweight z-score may be more appropriate to explore the relationship between growth retardation and adverse perinatal outcomes.

New population-based references for birth weight, length, and head circumference in singletons and twins from 23 to 43 gestation weeks

BACKGROUND AND OBJECTIVES

Birth size curves are needed for clinical and epidemiological purposes. We constructed birth weight (BW), length (BL), and head circumference (BHC) references, assessed effects of twinness and parity, and defined cut-off points for small, appropriate, and large for gestational age.

MATERIALS AND METHODS

Birth register data of all 753,036 infants born in 1996-2008 in Finland were cleaned to create references reflecting optimal intrauterine growth. The final data included 533,666 singletons and 15,033 twins (median gestation weeks (gws) 40.0 and 37.1, respectively, 41.6% primiparous). Sex-specific BW, BL, and BHC references were constructed from 23 to 43 gws separately for singletons and twins born to primiparous or multiparous mothers. GAMLSS method was used for modelling.

RESULTS

In singletons from 36 gws onwards, increased BW and BL were observed in comparison to previous reference from 1979-1983. Twins diverged from singletons from 30 gws onwards. At 37.0 gws, mean BW was 400 g lower and mean BL 1.2 cm shorter than in singletons. From 30 gws onwards, birth size was larger in infants of multiparous than primiparous mothers.

CONCLUSIONS

Population-based birth size references are available for the evaluation of birth size. Accounting for plurality and parity improves the accuracy of birth size evaluation.

Customized versus population approach for evaluation of fetal overgrowth

OBJECTIVE

To compare the ability of customized versus normalized population fetal growth norms in identifying neonates at risk for adverse perinatal outcomes (APOs) associated with fetal overgrowth and gestational diabetes (GDM).

STUDY DESIGN

Secondary analysis of a multicenter treatment trial of mild GDM. The primary outcome was a composite of neonatal outcomes associated with fetal overgrowth and GDM. Birth weight percentiles were calculated using ethnicity- and gender-specific population and customized norms (Gardosi).

RESULTS

Two hundred three (9.8%) and 288 (13.8%) neonates were large for gestational age by population (LGApop) and customized (LGAcust) norms, respectively. Both LGApop and LGAcust were associated with the primary outcome and neonatal hyperinsulinemia, but neither was associated with hypoglycemia or hyperbilirubinemia. The ability of customized and population birth weight percentiles for predicting APOs were poor (area under the receiver operating characteristic curve < 0.6 for six of eight APOs).

CONCLUSION

Neither customized nor normalized population norms better identify neonates at risk of APOs related to fetal overgrowth and GDM.

Customized growth charts for twin gestations to optimize identification of small-for-gestational age fetuses at risk of intrauterine fetal death

OBJECTIVE

Customized growth charts developed for singleton pregnancies have been shown to be more effective than population-based ones at identifying small-for-gestational age (SGA) fetuses at risk for intrauterine fetal death (IUFD). We sought to compare the association between SGA and IUFD in twins using customized growth charts designed for twin gestations compared to those designed for singletons.

METHODS

This was a retrospective cohort study using a database including singleton and twin pregnancies undergoing ultrasound examination between 16 and 20 weeks' gestation. After excluding preterm births < 34 weeks, congenital anomalies and stillbirths, we identified 51, 150 singleton births. Coefficients for significant physiological and pathological variables affecting birth weight for singletons were derived using backward stepwise multiple regression. The same process was repeated for twin births (1608 pairs), also adjusting for chorionicity. Customized growth charts for each pregnancy were derived using these two regression models for optimal birth weight at term and a proportionality equation. The association between SGA < 10(th) percentile, defined using the twin and singleton-customized charts, and IUFD were compared. Statistical analysis, including calculation of adjusted odds ratios (OR) for IUFD and screening accuracy using each chart, was performed.

RESULTS

The derived coefficients for optimal birth weight for twins were different from those for singletons, with lower constants and root mean square error (3422 and 288.9, respectively, in twins vs 3543 and 416 in singletons). Among 3786 twin infants, IUFD was seen in 123 (3.2%). The numbers of fetuses identified as SGA were 575 (15.2%) and 504 (13.3%) by the singleton and twin charts, respectively. Fetuses classified as SGA by the twin-specific customized charts were at a significantly increased risk for IUFD (adjusted OR, 2.3 (95% CI, 1.4-3.5)), whereas those classified as SGA by the singleton-customized charts were not (adjusted OR, 1.2 (95% CI, 0.7-2.0)).

CONCLUSION

Customized charts designed specifically for twins are more effective at identifying twin pregnancies at risk for IUFD than are those derived using singleton birth data.

Population versus customized fetal growth norms and adverse outcomes in an intrapartum cohort

OBJECTIVE

To compare population versus customized fetal growth norms in identifying neonates at risk for adverse outcomes (APO) associated with small for gestational age (SGA).

STUDY DESIGN

Secondary analysis of an intrapartum fetal pulse oximetry trial in nulliparous women at term. Birth weight percentiles were calculated using ethnicity- and gender-specific population norms and customized norms (Gardosi).

RESULTS

Of the studied neonates, 508 (9.9%) and 584 (11.3%) were SGA by population (SGApop) and customized (SGAcust) norms, respectively. SGApop infants were significantly associated with a composite adverse neonatal outcome, neonatal intensive care admission, low fetal oxygen saturation, and reduced risk of cesarean delivery; both SGApop and SGAcust infants were associated with a 5-minute Apgar score < 4. The ability of customized and population birth weight percentiles in predicting APO was poor (12 of 14 APOs had area under the curve of <0.6).

CONCLUSION

In this intrapartum cohort, neither customized nor normalized population norms adequately identified neonates at risk of APO related to SGA.

Adverse perinatal and neonatal outcomes and their determinants in rural Vietnam 1999-2005

Population-based estimations of perinatal and neonatal outcomes are sparse in Vietnam. There are no previously published data on small for gestational age (SGA) infants. A rural population in northern Vietnam was investigated from 1999 to 2005 (n=5521). Based on the birthweight distributions within the population under study, reference curves for intrauterine growth for Vietnamese infants were constructed and the prevalence and distribution of SGA was calculated for each sex. Neonatal mortality was estimated as 11.6 per 1000 live births and the perinatal mortality as 25.0 per 1000 births during the study period. The mean birthweight was 3112 g and the prevalence of low birthweight was 5.0%. The overall prevalence of SGA was 6.4%. SGA increased with gestational age and was 2.2%, 4.5% and 27.1% for preterm, term and post-term infants, respectively. Risk factors for SGA were post-term birth: adjusted odds ratio (AOR) 7.75 [95% CI 6.02, 9.98], mothers in farming occupations AOR 1.72 [95% CI 1.21, 2.45] and female infant AOR 1.61 [95% CI 1.27, 2.03]. There was a pronounced decrease in neonatal mortality after 33 weeks of gestation. Suggested interventions are improved prenatal identification of SGA infants by ultrasound investigation for fetal growth among infants who do not follow their expected clinical growth curve at the antenatal clinic. Other suggestions include allocating a higher proportion of preterm deliveries to health facilities with surgical capacity and neonatal care.

Graphic model of birth weight and gestational age in Monastir, Tunisia

BACKGROUND

Birth weight for gestational age curves provide to clinicians available references to assess fetal growth in individual infants and in populations. In Tunisia, until now, only North American based references were used. The objective of this study was to create national reference curves for birth weight and to compare these to those actually used in our maternities.

METHODS

A retrospective population based study was performed over a period of 11 years (from January 1994 to December 2004) using the register of births database of the region of Monastir. We studied a total of 75,751 births. Gestational age of infants ranged from 28 to 43 weeks. Fifth, tenth, 25th, 50th, 75th, 90th and 95th percentiles for weight were calculated by polynomial linear regression of the following general form to construct the clinical curves (Y=a+bX+cX(2)).

RESULTS

The database included 38,646 males and 37,105 females (sex ratio: 1.04). The resulting male and female curves provide smoothed percentiles cutoffs for defining small and large for gestational age births. An actual difference does exist between our curves and those routinely used.

CONCLUSION

These constructed smoothed gestational curves can be used as a useful tool for assessing birth weight and to evaluate clinical or public health interventions to enhance fetal growth.

Prenatal smoking cessation and the risk of delivering preterm and small-for-gestational-age newborns

OBJECTIVE

To examine the association between prenatal smoking cessation and delivery of a preterm or small-for-gestational-age (SGA) newborn in a large U.S. subpopulation using the revised (2003) birth certificate, which now assesses maternal smoking status by trimester.

METHODS

We analyzed a cohort of U.S.-resident, singleton births in the 11 states that used the revised birth certificate in 2005 (n=915,441). Self-reported maternal smoking status was categorized as "never smoked," "quit in the first trimester," "quit in the second trimester," and "smoked throughout" pregnancy (referent). Multinomial logistic regression was used to estimate adjusted odds ratios (aORs) for three outcomes (preterm non-SGA, term SGA, or preterm SGA newborns) by maternal smoking status. Analyses stratified by maternal age were also conducted.

RESULTS

Compared with women who smoked throughout pregnancy, first-trimester quitters reduced their odds of delivering a preterm non-SGA newborn by 31% (aOR 0.69, 95% confidence interval [CI] 0.65-0.74), a term SGA newborn by 55% (aOR 0.45, 95% CI 0.42-0.48), and a preterm SGA newborn by 53% (aOR 0.47, 95% CI 0.40-0.55), similar to nonsmokers. Second-trimester quitters also reduced their odds of delivering preterm non-SGA and term SGA newborns but to a lesser magnitude. When comparing first-trimester quitters with smokers in each age group, older mothers had generally lower odds of these outcomes than younger mothers.

CONCLUSION

Pregnant smokers who quit in the first trimester lowered their risk of delivering preterm and SGA newborns to a level similar to that of pregnant nonsmokers, and this benefit appeared to increase with maternal age. These findings reinforce current clinical guidance to encourage smoking cessation among pregnant smokers and serve as an additional incentive to quit.

LEVEL OF EVIDENCE

II.