Evaluation of gestational age estimate method on the calculation of preterm birth rates

The challenges of heterogeneity in gestational age and birthweight inclusion criteria for research synthesis on very preterm birth and childhood cognition: An umbrella review and meta-regression analysis

BACKGROUND

Meta-analyses of studies on very preterm (VPT) birth and childhood cognition select primary studies using gestational age inclusion criteria only, while others also include birthweight criteria. The consequences of this choice are unknown.

OBJECTIVE

The objective of this study was to describe the gestational age (GA) and birthweight (BW) criteria used in studies of VPT birth and cognition and to investigate whether meta-analysis results differ based on these criteria.

DATA SOURCES

Five systematic reviews on VPT birth and childhood IQ.

STUDY SELECTION AND DATA EXTRACTION

Country, birth years, GA-BW selection criteria and participant IQ were extracted from 156 studies representing 103 birth cohorts.

SYNTHESIS

Pooled standardised mean differences (SMD) in IQ between children born VPT and term-born controls were estimated by sub-group based on GA-BW criteria (GA, BW and GA-BW combined) and degree of preterm birth-low birthweight combinations: extremely preterm (EPT, <28 weeks) and extremely low BW (ELBW, <1000 g); VPT (<32 weeks) and very low BW (VLBW, <1500 g); and moderately MPT (<34 weeks) and moderately low BW (MLBW, <1800 g).

RESULTS

Cohorts used 27 distinct GA-BW inclusion criteria. Most common criteria were BW <1500 g (24 cohorts), BW <1000 g (12), GA <32 weeks (12) and GA <33 weeks (12); 23 studies used GA-BW combinations. BW-only criteria were more frequent in North America than Europe (63% versus 24%) and for cohorts before than after 1990 (67% vs 26%). Pooled SMD in IQ varied: SMD_EPT/ELBW -0.94, 95% confidence interval [CI] -1.07, -0.82; SMD_VPT/VLBW -0.78, 95% CI -0.85, -0.71; SMD_MPT/MLBW -0.68, 95% CI -0.79, -0.57; however, there was no difference in SMD across cohorts using BW compared to GA criteria after adjustment on risk group.

CONCLUSIONS

These findings support the inclusion of studies using GA and/or BW criteria in meta-analyses on VPT birth and cognition to increase the geographical and temporal generalisability of the results and to allow investigation of the impact of the heterogeneous inclusion criteria in this literature on outcomes.

Population-based rates, risk factors and consequences of preterm births in South-Asia and sub-Saharan Africa: A multi-country prospective cohort study

BACKGROUND

Preterm birth is the leading cause of neonatal deaths in low middle-income countries (LMICs), yet there exists a paucity of high-quality data from these countries. Most modelling estimates are based on studies using inaccurate methods of gestational age assessment. We aimed to fill this gap by measuring the population-based burden of preterm birth using early ultrasound dating in five countries in South-Asian and sub-Saharan Africa.

METHODS

We identified women early in pregnancy (<20 weeks based on last menstrual period) by home visits every 2-3 months (except in Zambia where they were identified at antenatal care clinics) in 5 research sites in South-Asia and sub-Saharan Africa between July 2012 and September 2016. Trained sonographers performed an ultrasound scan for gestational age dating. Women were enrolled if they were 8-19 weeks pregnant on ultrasound. Women <8 weeks were rescheduled for repeat scans after 4 weeks, and identified women were followed through pregnancy until 6 weeks postpartum. Site-specific rates and proportions were calculated and a logistic regression model was used to predict the risk factors of preterm birth.

RESULTS

Preterm birth rates ranged from 3.2% in Ghana to 15.7% in Pakistan. About 46% of all neonatal deaths occurred among preterm infants, 49% in South Asia and 40% in sub-Saharan Africa. Fourteen percent of all preterm infants died during the neonatal period. The mortality was 37.6% for early preterm babies (<34 weeks), 5.9% for late preterm babies (34 to <37 weeks), and 1.7% for term babies (37 to <42 weeks). Factors associated lower gestation at birth included South-Asian region (adjusted mean difference (Adj MD) = -6.2 days, 95% confidence interval (CI) = -5.5, -6.9), maternal morbidities (Adj MD = -3.4 days, 95% CI = -4.6, -2.2), multiple pregnancies (Adj MD = -17.8 days, 95% CI = -19.9,-15.8), adolescent pregnancy (Adj MD = -2.7 days, 95% CI = -3.7, -1.6) and lowest wealth quintile (Adj MD = -1.3 days, 95% CI = -2.4, -0.3).

CONCLUSIONS

Preterm birth rates are higher in South Asia than in sub-Saharan Africa and contribute to 49% and 40% of all neonatal deaths in the two regions, respectively. Adolescent pregnancy and maternal morbidities are modifiable risk factors associated with preterm birth.

Comparison of adverse birth outcomes among HIV-infected and HIV-uninfected women delivering in high and low risk settings in the era of universal ART in Malawi: a registry study

Background: Recent studies show that ART is associated with an adverse birth outcome in HIV-infected women.Aim: To compare rates of low birthweight (LBW) and preterm birth (PTB) between HIV-infected women receiving lifelong ART and HIV-uninfected women giving birth in low- and high-risk settings in Malawi.Methods: This observational, registry study was conducted from January 2016 to August 2017 in one large, tertiary referral hospital and four primary healthcare (PHC) facilities in Blantyre, Malawi. Women who delivered singleton live births or stillbirths of ≥20 weeks gestation were included in the analysis. Descriptive and stratified analyses were conducted using χ² tests and multivariable logistic models to control for maternal age, gravidity and health facility.Results: A total of 14,233 births were included in the analysis (7715 from the tertiary hospital and 6518 from PHC facilities). In the univariable analysis, there were no differences in rates of LBW (6.7% vs 6.4%) and PTB (42.5% vs 42.0%) between HIV-infected and -uninfected women delivering in PHC facilities. However, differences in LBW were significantly higher in HIV-infected women in multivariable analysis (LBW aOR 1.40, 95% CI 1.01-1.95). Rates of LBW and PTB were significantly higher in HIV-infected women than in uninfected women delivering at the tertiary hospital (LBW 17.6% vs 13.2%, aOR 1.53, 95% CI 1.27-1.85; PTB 28.2% vs 24.9%, aOR 1.37, 95% CI 1.17-1.60)Conclusion: Rates of adverse birth outcomes are significantly higher in HIV-infected women than in HIV-uninfected women, and this is more apparent in high-risk hospital settings than in low-risk PHC settings.

Epidemiology of late preterm and early term births - An international perspective

Late preterm (34-36 weeks of gestational age (GA)), and early term (37-38 weeks GA) birth rates among singleton live births vary from 3% to 6% and from 15% to 31%, respectively, across countries, although data from low- and middle-income countries are sparse. Countries with high preterm birth rates are more likely to have high early term birth rates; many risk factors are shared, including pregnancy complications (hypertension, diabetes), medical practices (provider-initiated delivery, assisted reproduction), maternal socio-demographic and lifestyle characteristics and environmental factors. Exceptions include nulliparity and inflammation which increase risks for preterm, but not early term birth. Birth before 39 weeks GA is associated with adverse child health outcomes across a wide range of settings. International rate variations suggest that reductions in early delivery are achievable; implementation of best practice guidelines for obstetrical interventions and public health policies targeting population risk factors could contribute to prevention of both late preterm and early term births.

Particulate Matter Exposure and Preterm Birth: Estimates of U.S. Attributable Burden and Economic Costs

BACKGROUND

Preterm birth (PTB) rates (11.4% in 2013) in the United States remain high and are a substantial cause of morbidity. Studies of prenatal exposure have associated particulate matter ≤ 2.5 μm in diameter (PM2.5) and other ambient air pollutants with adverse birth outcomes; yet, to our knowledge, burden and costs of PM2.5-attributable PTB have not been estimated in the United States.

OBJECTIVES

We aimed to estimate burden of PTB in the United States and economic costs attributable to PM2.5 exposure in 2010.

METHODS

Annual deciles of PM2.5 were obtained from the U.S. Environmental Protection Agency. We converted PTB odds ratio (OR), identified in a previous meta-analysis (1.15 per 10 μg/m3 for our base case, 1.07-1.16 for low- and high-end scenarios) to relative risk (RRs), to obtain an estimate that better represents the true relative risk. A reference level (RL) of 8.8 μg/m3 was applied. We then used the RR estimates and county-level PTB prevalence to quantify PM2.5-attributable PTB. Direct medical costs were obtained from the 2007 Institute of Medicine report, and lost economic productivity (LEP) was estimated using a meta-analysis of PTB-associated IQ loss, and well-established relationships of IQ loss with LEP. All costs were calculated using 2010 dollars.

RESULTS

An estimated 3.32% of PTBs nationally (corresponding to 15,808 PTBs) in 2010 could be attributed to PM2.5 (PM2.5 > 8.8 μg/m3). Attributable PTBs cost were estimated at $5.09 billion [sensitivity analysis (SA): $2.43-9.66 B], of which $760 million were spent for medical care (SA: $362 M-1.44 B). The estimated PM2.5 attributable fraction (AF) of PTB was highest in urban counties, with highest AFs in the Ohio Valley and the southern United States.

CONCLUSIONS

PM2.5 may contribute substantially to burden and costs of PTB in the United States, and considerable health and economic benefits could be achieved through environmental regulatory interventions that reduce PM2.5 exposure in pregnancy. Citation: Trasande L, Malecha P, Attina TM. 2016. Particulate matter exposure and preterm birth: estimates of U.S. attributable burden and economic costs. Environ Health Perspect 124:1913-1918; http://dx.doi.org/10.1289/ehp.1510810.

Comparison of gestational dating methods and implications for exposure-outcome associations: an example with PM2.5 and preterm birth

OBJECTIVES

Estimating gestational age is usually based on date of last menstrual period (LMP) or clinical estimation (CE); both approaches introduce potential bias. Differences in methods of estimation may lead to misclassification and inconsistencies in risk estimates, particularly if exposure assignment is also gestation-dependent. This paper examines a 'what-if' scenario in which alternative methods are used and attempts to elucidate how method choice affects observed results.

METHODS

We constructed two 20-week gestational age cohorts of pregnancies between 2000 and 2005 (New Jersey, Pennsylvania, Ohio, USA) using live birth certificates: one defined preterm birth (PTB) status using CE and one using LMP. Within these, we estimated risk for 4 categories of preterm birth (PTBs per 10⁶ pregnancies) and risk differences (RD (95% CIs)) associated with exposure to particulate matter (PM_2.5).

RESULTS

More births were classified preterm using LMP (16%) compared with CE (8%). RD divergences increased between cohorts as exposure period approached delivery. Among births between 28 and 31 weeks, week 7 PM_2.5 exposure conveyed RDs of 44 (21 to 67) for CE and 50 (18 to 82) for LMP populations, while week 24 exposure conveyed RDs of 33 (11 to 56) and -20 (-50 to 10), respectively.

CONCLUSIONS

Different results from analyses restricted to births with both CE and LMP are most likely due to differences in dating methods rather than selection issues. Results are sensitive to choice of gestational age estimation, though degree of sensitivity can vary by exposure timing. When both outcome and exposure depend on estimate of gestational age, awareness of nuances in the method used for estimation is critical.

Predicting Preterm Birth Among Women Screened by North Carolina's Pregnancy Medical Home Program

OBJECTIVE

To determine which combination of risk factors from Community Care of North Carolina's (CCNC) Pregnancy Medical Home (PMH) risk screening form was most predictive of preterm birth (PTB) by parity and race/ethnicity.

METHODS

This retrospective cohort included pregnant Medicaid patients screened by the PMH program before 24 weeks gestation who delivered a live birth in North Carolina between September 2011-September 2012 (N = 15,428). Data came from CCNC's Case Management Information System, Medicaid claims, and birth certificates. Logistic regression with backward stepwise elimination was used to arrive at the final models. To internally validate the predictive model, we used bootstrapping techniques.

RESULTS

The prevalence of PTB was 11 %. Multifetal gestation, a previous PTB, cervical insufficiency, diabetes, renal disease, and hypertension were the strongest risk factors with odds ratios ranging from 2.34 to 10.78. Non-Hispanic black race, underweight, smoking during pregnancy, asthma, other chronic conditions, nulliparity, and a history of a low birth weight infant or fetal death/second trimester loss were additional predictors in the final predictive model. About half of the risk factors prioritized by the PMH program remained in our final model (ROC = 0.66). The odds of PTB associated with food insecurity and obesity differed by parity. The influence of unsafe or unstable housing and short interpregnancy interval on PTB differed by race/ethnicity.

CONCLUSIONS

Evaluation of the PMH risk screen provides insight to ensure women at highest risk are prioritized for care management. Using multiple data sources, salient risk factors for PTB were identified, allowing for better-targeted approaches for PTB prevention.

Validity of pre and post-term birth rates based on the date of last menstrual period compared to early obstetric ultrasonography

The aim of this study was to assess the validity of the last menstrual period (LMP) estimate in determining pre and post-term birth rates, in a prenatal cohort from two Brazilian cities, São Luís and Ribeirão Preto. Pregnant women with a single fetus and less than 20 weeks' gestation by obstetric ultrasonography who received prenatal care in 2010 and 2011 were included. The LMP was obtained on two occasions (at 22-25 weeks gestation and after birth). The sensitivity of LMP obtained prenatally to estimate the preterm birth rate was 65.6% in São Luís and 78.7% in Ribeirão Preto and the positive predictive value was 57.3% in São Luís and 73.3% in Ribeirão Preto. LMP errors in identifying preterm birth were lower in the more developed city, Ribeirão Preto. The sensitivity and positive predictive value of LMP for the estimate of the post-term birth rate was very low and tended to overestimate it. LMP can be used with some errors to identify the preterm birth rate when obstetric ultrasonography is not available, but is not suitable for predicting post-term birth.

Investigating Implausible Gestational Age and High Birthweight Combinations

BACKGROUND

Birth certificate data overestimate national preterm births because a high percentage of last menstrual period (LMP) dates have errors. Study goals were to determine: (i) To what extent errors in transfer of birthweight and LMP date from medical records to birth certificates contribute to implausibly high birthweight-for-gestational-age births; (ii) What percentage of implausible births would be resolved if the clinical estimate (CE) from birth certificates were used instead of LMP-based gestational age, and with what degree of certainty; and (iii) Of those not resolved, what percentage had a medical explanation.

METHODS

Medical records and birth certificates for all singleton infants with implausibly high birthweight-for-gestational-age based on LMP delivered in the Kaiser Permanente Northwest system in Oregon during 1998-2007 were examined. Percentages of implausible records resolved under various scenarios were calculated.

RESULTS

A total of 100 births with implausibly high birthweight-for-gestational age combinations were identified. When LMP date and birthweight from medical records were used instead of from birth certificates, 31% of births with implausible combinations were resolved. Substituting the CE on the birth certificate for the LMP date resolved 92%. Of the latter, the clinician's gestational age estimate in the medical record was obtained in early pregnancy in 72%. Five of the eight births with unresolved implausible combinations were to mothers with diabetes; the remaining three had no documented medical explanation.

CONCLUSIONS

In this study, use of the birth certificate CE rather than the LMP resulted in a clinically reliable reclassification for the majority of implausible birthweight-for-gestational age deliveries.

What contributes to disparities in the preterm birth rate in European countries?

PURPOSE OF REVIEW

In countries with comparable levels of development and healthcare systems, preterm birth rates vary markedly--a range from 5 to 10% among live births in Europe. This review seeks to identify the most likely sources of heterogeneity in preterm birth rates, which could explain differences between European countries.

RECENT FINDINGS

Multiple risk factors impact on preterm birth. Recent studies reported on measurement issues, population characteristics, reproductive health policies as well as medical practices, including those related to subfertility treatments and indicated deliveries, which affect preterm birth rates and trends in high-income countries. We showed wide variation in population characteristics, including multiple pregnancies, maternal age, BMI, smoking, and percentage of migrants in European countries.

SUMMARY

Many potentially modifiable population factors (BMI, smoking, and environmental exposures) as well as health system factors (practices related to indicated preterm deliveries) play a role in determining preterm birth risk. More knowledge about how these factors contribute to low and stable preterm birth rates in some countries is needed for shaping future policy. It is also important to clarify the potential contribution of artifactual differences owing to measurement.

Standard methods based on last menstrual period dates misclassify and overestimate US preterm births

OBJECTIVE

To compare number of US preterm births based on obstetric versus last menstrual period (LMP) estimates and evaluate their correlations with clinical risk indicators associated with prematurity.

STUDY DESIGN

Preterm births were assessed from LMP, per standard practice, and, separately, from obstetric estimates using the 2012 Natality Public Use File. Percentages of infants with neonatal intensive care unit (NICU) admission and low birth weight (LBW) were calculated.

RESULT

More births were <37 weeks gestational age (GA) by reported LMP (11.4%) versus obstetric estimates (9.5%). Among infants preterm by LMP, but born at 37-41 weeks by obstetric estimates, there were 5.7% NICU admission and 7.7% LBW rates versus 25.2% and 35.4%, respectively, of those preterm by obstetric estimates but born 37-41 weeks by LMP assessments.

CONCLUSION

Obstetric estimates provide the most clinically relevant estimates of US preterm births. Assessments calculated from LMP alone may overestimate prematurity incidence by ~20%.

Determining gestational age based on information from the Birth in Brazil study

This study aimed at assessing the validity of different measures for estimating gestational age and to propose the creation of an algorithm for gestational age at birth estimates for the Birth in Brazil survey--a study conducted in 2011-2012 with 23,940 postpartum women. We used early ultrasound imaging, performed between 7-20 weeks of gestation, as the reference method. All analyses were performed stratifying by payment of maternity care (public or private). When compared to early ultrasound imaging, we found a substantial intraclass correlation coefficient of ultrasound-based gestational age at admission measure (0.95 and 0.94) and of gestational age reported by postpartum women at interview measure (0.90 and 0.88) for the public and private payment of maternity care, respectively. Last menstrual period-based measures had lower intraclass correlation coefficients than the first two measures evaluated. This study suggests caution when using the last menstrual period as the first measure for estimating gestational age in Brazil, strengthening the use of information obtained from early ultrasound imaging results.