Assessing the quality of last menstrual period date on California birth records

Birth certificate last menstrual period (LMP) date is widely used to estimate gestational age in the US. While data quality concerns have been raised, no large population-based study has isolated data quality issues by comparing birth record LMP (Birth LMP) with reliable LMP dates from another source. We assessed LMP data quality in 2002 California singleton livebirth records ( n  = 515 381) and in a subset of records with linked prenatally collected LMP from California's statewide Prenatal Expanded Alpha-fetoprotein Screening Program (XAFP) ( n  = 105 936). Missing or incomplete LMP data affected 13% of birth records; 17% of those had complete LMP within XAFP records.
Data quality indicators supported XAFP LMP as more accurate than Birth LMP, with a lower prevalence of digit preference, post-term delivery, out-of-range gestational age estimates and implausible birthweight-for-gestational age. The bimodal birthweight distribution evident at 20–31 weeks' gestation based on Birth LMP was nearly absent with XAFP LMP-based gestational age. Approximately 32% of the second birthweight mode was explained by apparent clerical errors in Birth LMP month. Digit preference errors, particularly day 1, were associated with gestational age overestimation. Preterm delivery rates were higher according to Birth (7.6%) vs. XAFP LMP (7.2%). One-fifth of observed preterm and over half of observed post-term births using Birth LMP were not true cases; 15% of true preterm cases were missed. African American or Hispanic, less educated, and publicly or uninsured women were most likely to be misclassified and have large LMP date discrepancies attributable to clerical or digit preference error. The implementation of a revised birth certificate is an opportunity for targeted training and data entry checks that could substantially improve LMP accuracy on birth records.     

Comparison of gestational age at birth based on last menstrual period and ultrasound during the first trimester

Reported last menstrual period (LMP) is commonly used to estimate gestational age (GA) but may be unreliable. Ultrasound in the first trimester is generally considered a highly accurate method of pregnancy dating. The authors compared first trimester report of LMP and first trimester ultrasound for estimating GA at birth and examined whether disagreement between estimates varied by maternal and infant characteristics. Analyses included 1867 singleton livebirths to women enrolled in a prospective pregnancy cohort. The authors computed the difference between LMP and ultrasound GA estimates (GA difference) and examined the proportion of births within categories of GA difference stratified by maternal and infant characteristics. The proportion of births classified as preterm, term and post‐term by pregnancy dating methods was also examined. LMP‐based estimates were 0.8 days (standard deviation = 8.0, median = 0) longer on average than ultrasound estimates. LMP classified more births as post‐term than ultrasound (4.0% vs. 0.7%). GA difference was greater among young women, non‐Hispanic Black and Hispanic women, women of non‐optimal body weight and mothers of low‐birthweight infants. Results indicate first trimester report of LMP reasonably approximates gestational age obtained from first trimester ultrasound, but the degree of discrepancy between estimates varies by important maternal characteristics.     

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.     

Menstrual versus clinical estimate of gestational age dating in the United States: temporal trends and variability in indices of perinatal outcomes

Accurate estimation of gestational age early in pregnancy is paramount for obstetric care decisions and for determining fetal growth and other conditions that may necessitate timing the iatrogenic intervention or delivery. We sought to examine temporal changes in the distributions of two measures of gestational age, namely, those based on menstrual dating and a clinical estimate. We further sought to evaluate relative comparisons and variability in indices of perinatal outcomes. We utilised the Natality data files in the US, 1990–2002 comprising women that delivered a singleton livebirth between 22 and 44 weeks gestation ( n  = 42 689 603).
Changes were shown in the distributions of gestational age based on menstrual vs. clinical estimate between 1990 and 2002, as well as changes in the proportions of preterm (<37, <32 and <28 weeks) and post-term (≥42 weeks) birth, and small- (SGA; <10th percentile) and large-for-gestational-age (LGA; birthweight >90th percentile) births. While the absolute rates of preterm birth <37 weeks, SGA and LGA births were lower based on the clinical estimate of gestational age relative to that based on menstrual dating, the increases in preterm birth rate between 1990 and 2002 were fairly similar between the two measures of gestational dating. However, the decline in post-term births was larger, based on the clinical estimate (−73.8%), than on the menstrual estimate (−36.6%) between 1990 and 2002. While the clinical estimate of gestational age appears to provide a reasonably good approximation to the menstrual estimate, disregarding the clinical estimate of gestational age may ignore the advantages of gestational age assessment in modern obstetrics.     

Ethnic variation in postnatal assessments of gestational age: a reappraisal

While the possibility of an ethnic bias in postnatal assessments of gestational age has been suggested by several investigators, others have reported that postnatal assessments do not provide biased estimates in non-White ethnic groups. In the light of this ongoing controversy, this study examines the validity of the Ballard postnatal assessment of gestational age by ethnicity, using a relatively large hospital data base that allows for the inspection of ethnic variations in the agreement between the Ballard assessment and last menstrual period (LMP). The results indicate that there is a greater over-estimation of the LMP interval by the Ballard method in Blacks compared with Whites and suggest that systematic differences exist by ethnicity of mother in the agreement between the Ballard postnatal assessment and the LMP interval. After taking maternal characteristics and pregnancy complications into account, for a given gestational age interval, Blacks have on average a greater level of maturity as measured by Ballard. One interpretation of these findings is that postnatal assessments may provide biased over-estimates of the LMP gestational age interval in certain ethnic groups. An alternative interpretation of these data is that the gestational age interval based on LMP is not a valid indicator of fetal maturity, readiness for birth and infant risk status across all ethnic groups.     

Determining Gestational Age in a Low-resource Setting: Validity of Last Menstrual Period

The validity of three methods (last menstrual period [LPM], Ballard and Dubowitz scores) for assessment of gestational age for premature infants in a low-resource setting was assessed, using antenatal ultrasound as the gold standard. It was hypothesized that LMP and other methods would perform similarly in determining postnatal gestational age. Concordance analysis was applied to data on 355 neonates of <33 weeks gestational age enrolled in a topical skin-therapy trial in a tertiary-care children''s hospital in Bangladesh. The concordance coefficient for LMP, Ballard, and Dubowitz was 0.878, 0.914, and 0.886 respectively. LMP and Ballard underestimated gestational age by one day (±11) and 2.9 days (±7.8) respectively while Dubowitz overestimated gestational age by 3.9 days (±7.1) compared to ultrasound finding. LMP in a low-resource setting was a more reliable measure of gestational age than previously thought for estimation of postnatal gestational age of preterm infants. Ballard and Dubowitz scores are slightly more reliable but require more technical skills to perform. Additional prospective trials are warranted to examine LMP against antenatal ultrasound for primary assessment of neonatal gestational age in other low-resource settings.Key words: Gestational age, Last menstrual period, Neonatal health, Obstetrics, Bangladesh     

Last menstrual period provides the best estimate of gestation length for women in rural Guatemala

The accurate estimation of gestational age in field studies in rural areas of developing countries continues to present difficulties for researchers. Our objective was to determine the best method for gestational age estimation in rural Guatemala. Women of childbearing age from four communities in rural Guatemala were invited to participate in a longitudinal study. Gestational age at birth was determined by an early second trimester measure of biparietal diameter, last menstrual period (LMP), the Capurro neonatal examination and symphysis-fundus height (SFH) for 171 women-infant pairs. Regression modelling was used to determine which method provided the best estimate of gestational age using ultrasound as the reference. Gestational age estimated by LMP was within +/-14 days of the ultrasound estimate for 94% of the sample. LMP-estimated gestational age explained 46% of the variance in gestational age estimated by ultrasound whereas the neonatal examination explained only 20%. The results of this study suggest that, when trained field personnel assist women to recall their date of LMP, this date provides the best estimate of gestational age. SFH measured during the second trimester may provide a reasonable alternative when LMP is unavailable.     

Factors influencing the relationship between a newborn assessment of gestational maturity and the gestational age interval

Summary. This study examines the correlation and agreement between the calculated 'gestational interval' from the date of last menstrual period (LMP) and the Ballard newborn assessment of gestational maturity. It then investigates selected maternal socio-demographic, prenatal, intrapartum and infant factors which may account for differences between these two gestational age determination methods. Single live-born deliveries (n = 10 794) were selected from a 1982–1986 medical university perinatal information data system for analysis. The Ballard assessment overestimates the LMP at earlier gestational ages and underestimates in the post-term range. The discrepancy between LMP and Ballard varies across the range of gestational age values and the extent of variation differs by several maternal and infant risk factors. These findings suggest considerable bias may result from the indiscriminate case mixing of LMP and Ballard values for use in gestational age research or in standardising developmental tests. We highlight the deficiencies in using correlation coefficients or mean differences to assess agreement between these measures.     

Factors influencing the relationship between a newborn assessment of gestational maturity and the gestational age interval

This study examines the correlation and agreement between the calculated 'gestational interval' from the date of last menstrual period (LMP) and the Ballard newborn assessment of gestational maturity. It then investigates selected maternal socio-demographic, prenatal, intrapartum and infant factors which may account for differences between these two gestational age determination methods. Single live-born deliveries (n = 10,794) were selected from a 1982-1986 medical university perinatal information data system for analysis. The Ballard assessment overestimates the LMP at earlier gestational ages and underestimates in the post-term range. The discrepancy between LMP and Ballard varies across the range of gestational age values and the extent of variation differs by several maternal and infant risk factors. These findings suggest considerable bias may result from the indiscriminate case mixing of LMP and Ballard values for use in gestational age research or in standardising developmental tests. We highlight the deficiencies in using correlation coefficients or mean differences to assess agreement between these measures.     

Variation between last-menstrual-period and clinical estimates of gestational age in vital records

An accurate assessment of gestational age is vital to population-based research and surveillance in maternal and infant health. However, the quality of gestational age measurements derived from birth certificates has been in question. Using the 2002 US public-use natality file, the authors examined the agreement between estimates of gestational age based on the last menstrual period (LMP) and clinical estimates in vital records across durations of gestation and US states and explored reasons for disagreement. Agreement between the LMP and the clinical estimate of gestational age varied substantially across gestations and among states. Preterm births were more likely than term births to have disagreement between the two estimates. Maternal age, maternal education, initiation of prenatal care, order of livebirth, and use of ultrasound had significant independent effects on the disagreement between the two measures, regardless of gestational age, but these factors made little difference in the magnitude of gestational age group differences. Information available on birth certificates was not sufficient to understand this disparity. The lowest agreement between the LMP and the clinical estimate was observed among preterm infants born at 28-36 weeks' gestation, who accounted for more than 90% of total preterm births. This finding deserves particular attention and further investigation.     

Assessing number-specific error in the recall of onset of last menstrual period

The goal of this investigation was to determine whether women who did not report preferred numbers for their last menstrual period (LMP) may be a group of women who are particularly careful in keeping track of their menstrual cycles and therefore have more accurate LMP dating--based on a comparison with ultrasound examinations. We also sought to estimate the frequency with which preferred numbers are reported in different sources of data and for different subgroups of women. First, we examined the 1987 California birth certificates in which LMP was collected at the time of birth (n = 504853). We also examined the records of 43880 women participating in the California Alpha-fetoprotein (AFP) Screening Program between 1986 and 1987, for whom gestational ages based on both early ultrasound examination and LMP were collected before 20 weeks of gestation. In the 1987 California birth certificates, seven numbers--1, 5, 10, 15, 20, 25 and 28--were recorded more frequently than expected. An estimated 12.9% of these records had preferred numbers. The most frequently recorded number was 15, occurring 2.5 times more often than expected (P < 0.01). In the data of the AFP Screening Program, the same seven numbers were preferred, and approximately 7.9% of records were affected by number preference. Comparisons with measurements of gestational age based on ultrasound demonstrated that LMP-based gestational ages in which non-preferred numbers are reported for the LMP are slightly more accurate than those in which preferred numbers are reported (P < 0.01). In most cases, number preference appears to introduce small errors into measurements of gestational age, probably as a result of rounding. Thus, the effect of number preference may be primarily of interest to research studies in which small errors in the measurement of gestational age will have a significant impact on findings.     

Comparative accuracy of clinical estimate versus menstrual gestational age in computerized birth certificates

OBJECTIVE: This study compares gestational age data obtained by clinical estimate with data calculated from the date of the last menstrual period (LMP) as recorded on birth certificates. METHODS: The authors analyzed 476,034 computerized birth records from three overlap years, that is, those that contained both menstrual and clinical estimates of gestational age, concentrating on cases within the biologically plausible range of 20-44 weeks. RESULTS: The overall exact concordance between the two measurements was 46%. For +1 week it was 78%, and for +2 weeks it was 87%. Incidence of prematurity was 16% with menstrual gestational age, while it was 12% with clinical estimate. About 47% of the LMP-based preterm births were classified as term by clinical estimate. Eighty-three percent of clinical estimate-based preterms were also preterms by LMP-based gestation. Birthweight frequency distribution curves for LMP-based gestational age are bimodal, indicating probable miscoding of term births. An apparent over-representation of births coded as exactly 40 weeks by clinical estimate suggests rounding off near term for this method. CONCLUSION: Agreement between menstrual and clinical estimates of gestational age occurs most often close to term, with significant disagreement in preterm and postterm births. Use of different methods of determining gestation in different years or geographic populations will result in artifactual differences in important indicators such as prematurity rate.     

Alpha-fetoprotein screening for open spina bifida: effect of routine biparietal diameter measurement to estimate gestational age

The estimation of gestational age by "dates" (time since the first day of the last menstrual period) and by means of an ultrasound scan examination (measurement of fetal biparietal diameter) lead to different results when screening for open spina bifida by maternal serum alphafetoprotein (A.F.P.) measurement. This paper provides estimates of the detection rate for open spina bifida, the false positive rate, and the odds of being affected given a positive A.F.P. result when gestational age is estimated according to the two methods. Estimates are also given on the odds of being affected for individuals with a particular serum A.F.P. result. The estimates may be useful to those concerned with the development and design of screening programmes for open spina bifida as well as to clinicians concerned with providing risk estimates for individual patients.     

United States vital statistics and the measurement of gestational age

Estimates of the gestational age of the newborn based on US Birth Certificate data are extensively used to monitor trends in infant and maternal health and to improve our understanding of adverse pregnancy outcome. Two measures of gestational age, the 'date of the last normal menses' (LMP) and the 'clinical estimate of gestation' (CE), have been available from birth certificate data since 1989. Reporting irregularities with the LMP-based measure are well-documented, and important questions remain regarding the derivation of the CE. Changes in perinatal medicine and in vital statistics reporting in recent years may have importantly altered gestational age data based on vital statistics. This study describes how gestational age measures are collected and edited in US national vital statistics, and examines changes in the reporting of these measures by race and Hispanic origin between 1990 and 2002. Data are drawn from the National Center for Health Statistics' restricted use US birth files for 1990–2002. Bivariable statistics are used.
The percentage of records with missing LMP dates declined markedly over the study period, overall, and for each racial/Hispanic origin group studied. A marked shift in the distribution of the CE of gestational age was also observed, suggesting changes both in the true distribution of age at birth, and in the derivation of this measure. Agreement between the LMP-based and CE estimates increased over the study period, especially among preterm births. However, a high proportion of LMP dates continue to be missing or invalid and the derivation of the CE is still uncertain. In sum, although the reporting of gestational age measures in vital statistics appears to have improved between 1990 and 2002, substantial concerns with both the LMP-based and the CE persist. Efforts to identify approaches to further improve upon the quality of these data are needed.     

Evaluation of Gestational Age Estimate Method on the Calculation of Preterm Birth Rates

The objectives of this study is to evaluate the impact of vital record gestational age estimation method on resulting preterm birth (PTB) rate calculations. This retrospective analysis reviewed three methods of gestational age estimation using all Ohio live birth records from 2006 to 2009. PTB rates were calculated using each gestational age representation and agreement between classifications of PTB was evaluated with respect to maternal age and race. For each of 608,530 births, gestational age estimates based on last menstrual period (LMP) were compared to clinically-based obstetric estimates. When gestational age estimates did not perfectly agree, differences in the consequential classification of PTB status were evaluated with respect to a third reconciliatory combined gestational age estimate. Mean birth weight at each week of gestation was calculated and compared for all three estimate methods. Substantial agreement was found in PTB classification among gestational age estimates (kappa: 0.748; 95 % Confidence Interval: 0.745–0.750); agreement was weakest among black mothers and among mothers less than 20 years of age. LMP-based gestational age estimates did not perfectly agree with obstetric estimates in 238,262 records (39.2 %). Disagreement in gestational age led to disagreement in PTB status in 32,033 records (5.3 % of total cases) resulting in a 1.8 percentage point difference in PTB rate calculations (11.0 % using obstetric and 12.8 % using combined estimates). Researchers and policy makers need consistency in selecting which gestational age estimate method to use when calculating or comparing PTB rates.     

Expanding medical abortion: can medical abortion be effectively provided without the routine use of ultrasound?

Medical abortion studies have traditionally relied on ultrasound to confirm gestational age, intrauterine location and abortion completion. However, the routine dependence on ultrasound can limit access to safe services for women living in low resource settings that are often most in need of safe abortion care. This review discusses the literature surrounding the safe provision of medical abortion without the routine use of ultrasonography and concludes that clinicians can use the reported last menstrual period (LMP) and physical examination to reasonably estimate gestational age. Completed pregnancy expulsion can be confirmed primarily through history and physical examination with some studies indicating that urine pregnancy tests may also play a limited role. Central to the discussion of whether medical abortion can be provided in most low resource settings without the routine use of ultrasonography is the fact that the mifepristone–misoprostol regimen is a highly effective procedure for pregnancy termination through 63 days' gestation.     

The accuracy of using last menstrual period to determine gestational age for first trimester medication abortion: a systematic review

Objective

We sought to evaluate the accuracy of assessing gestational age (GA) prior to first trimester medication abortion using last menstrual period (LMP) compared to ultrasound (U/S).

Study Design

We searched Medline, Embase and Cochrane databases through October 2013 for peer-reviewed articles comparing LMP to U/S for GA dating in abortion care. Two teams of investigators independently evaluated data using standard abstraction forms. The US Preventive Services Task Force and Quality Assessment of Diagnostic Accuracy Studies guidelines were used to assess quality.

Results

Of 318 articles identified, 5 met inclusion criteria. Three studies reported that 2.5–11.8% of women were eligible for medication abortion by LMP and ineligible by U/S. The number of women who underestimated GA using LMP compared to U/S ranged from 1.8 to 14.8%, with lower rates found when the sample was limited to a GA < 63 days. Most women (90.5–99.1%) knew their LMP, 70.8–90.5% with certainty.

Conclusion

Our results support that LMP can be used to assess GA prior to medication abortion at GA < 63 days. Further research looking at patient outcomes and identifying women eligible for medication abortion by LMP but ineligible by U/S is needed to confirm the safety and effectiveness of providing medication abortion using LMP alone to determine GA.     

Birthweight distributions by gestational age: comparison of LMP-based and ultrasound-based estimates of gestational age using data from the Swedish Birth Registry

Studies based on data from the US have reported that the birthweight distribution at gestational age 28–31 weeks is bimodal with a second peak occurring at approximately 3300 g, suggesting that there is misclassification of term infants. In these studies, gestational ages were estimated from the date of the last menstrual period (LMP), and it has been suggested that ultrasound-based estimates of gestational age would eliminate the problem with bimodal birthweight distributions. Swedish data include both measures, thus offering an opportunity for comparison. All singleton births in Sweden from 1993 to 2002 with information on birthweight were included in the study ( n  = 917 901). Both LMP- and ultrasound-based estimates of gestational age were available for 75.1% of the births. Two possible sources of misclassification were considered: measurement error, assuming that ultrasound-based estimates are better, and data entry errors. An algorithm for assessment of data entry errors was developed; 67.4% of the births were left for the analyses of data 'cleaned' from data entry errors.
Based on the entire study population, the LMP-based birthweight curves for lower-gestational-age preterm births were bimodal, with a second peak around 3500 g. The bimodal distribution was greatly attenuated when using ultrasound-based gestational age categories, but did not disappear. After cleaning the data, the LMP-based birthweight distributions for infants at gestational ages <32 weeks were no longer bimodal, and were very similar to the ultrasound-based curves. In conclusion, data entry errors are more likely to cause the bimodality in the birthweight distribution among preterm infants than measurement errors in the LMP-based gestational age estimate.     

Characteristics of prospectively measured vaginal bleeding among women trying to conceive

Previous research has described variability in menstrual cycle lengths within and across women, though less attention has focused on characterising patterns of bleeding. While clinical definitions for menstrual bleeding are often given in standard textbooks, the validity of conventional definitions has not been empirically evaluated in epidemiological studies. The definition of menstrual bleeding may affect the analysis of time to pregnancy and pregnancy dating that relies upon the last menstrual period. We used daily records of vaginal bleeding from a prospective cohort study that included 74 women trying to become pregnant who reported 430 bleeding episodes. A longitudinal mixture model (PROC TRAJ) was used to classify patterns of bleeding.
Among the first 74 bleeding episodes, 15% comprised only days with spotting or light bleeding (possibly representing non-menstrual bleeding given the length of the cycle defined by these bleeding episodes). When all 430 bleeding episodes were analysed, four distinct bleeding patterns emerged: (1) episodic bleeding comprising 1–3 days of spotting (10%), (2) bleeding lasting 3–6 days (40%), (3) bleeding lasting 6–8 days (33%), and (4) bleeding lasting 8–12 days (17%). These findings suggest that non-menstrual bleeding may be relatively common. Considerable variation in menstrual bleeding patterns is evident, and as such is likely to impact fecundity-related endpoints or gestational age estimates that rely upon menstrual cycle dates. The association between bleeding patterns and female fecundity awaits future research.     

Methods of gestational age assessment influence the observed association between antiretroviral therapy exposure,preterm delivery,and small-for-gestational age infants: a prospective study in Cape Town,South Africa

PurposeHeterogeneous findings exist on antiretroviral therapy (ART) use in pregnancy and preterm delivery (PTD) or infants born small-for-gestational age (SGA). Whether reported differences may be explained by methods used to ascertain gestational age (GA) has not been explored.MethodsWe enrolled consecutive pregnant women attending a large primary care antenatal clinic in South Africa. Public-sector midwives assessed GA by last menstrual period (LMP) and symphysis-fundal height (SFH). Separately, if clinical GA was less than 24 weeks, ultrasound (US) was performed by a research sonographer blinded to midwife assessments. In analysis, the impact of measurement error on the association between HIV/ART status and birth outcome by GA method was assessed, and factors associated with clinical GA underestimation or overestimation identified.ResultsIn 1787 women included overall, estimated PTD incidence was 36% by LMP, 17% by SFH, and 11% by US. PTD risk was higher for HIV-infected than HIV-uninfected women using US-GA (adjusted odds ratio [aOR] 1.95; 95% CI 1.10–3.46); for LMP/SFH-GA, the associations were smaller and not significant. These findings persisted after adjustment for age, parity, height, and previous PTD. PTD risk did not vary by timing of ART initiation (before or during pregnancy) for any method. Elevated BMI and older age were associated with decreased risk of underestimation by both LMP and SFH; HIV status and obesity were associated with increased risk of overestimation by SFH. There were no differences in SGA incidence across GA methods.ConclusionsFindings for an association between HIV/ART and birth outcomes are substantially influenced by GA assessment method. With growing public health interest in this association, future research efforts should seek to standardize optimal measures of gestation.