Menstrual Period Estimates Research Articles

Preterm disparities between foreign and Swedish born mothers depend on the method used to estimate gestational age. A Swedish population-based register study.

This study aims to examine whether disparities in gestational age outcomes between foreign and Swedish-born mothers are contingent on the measure used to estimate gestational age and, if so, to identify which maternal factors are associated with the discrepancy. Using population register data, we studied all singleton live births in Sweden from 1992-2012 (n = 1,317,265). Multinomial logistic regression was performed to compare gestational age outcomes classified into very (<32 weeks) and late preterm (32-36 weeks), term and post-term derived from the last menstrual period (LMP) and ultrasound estimates in foreign- and Swedish-born women. Compared to Swedish-born women, foreign-born women had similar odds of very preterm birth (OR: 0.98 [95% CI: 0.98, 1.01]) and lower odds of moderately preterm birth (OR: 0.95 [95% CI: 0.92, 0.98]) based on ultrasound, while higher risks based on LMP (respectively, OR: 1.10 [95% CI: 1.07, 1.14] and 1.09 [95% CI: 1.06, 1.13]). Conclusions on disparities in gestational age-related outcomes by mother's country of origin depend on the method used to estimate gestational age. Except for very preterm, foreign-born women had a health advantage when gestational age is based on ultrasound, but a health disadvantage when based on LMP. Studies assessing disparities in very preterm birth by migration status are not affected by the estimation method but caution should be taken when interpreting disparities in moderately preterm and preterm birth rates.

Quantifying bias between reported last menstrual period and ultrasonography estimates of gestational age in Lusaka, Zambia.

To quantify differences in assessing preterm delivery when calculating gestational age from last menstrual period (LMP) versus ultrasonography biometry. The Zambian Preterm Birth Prevention Study is an ongoing prospective cohort study that commenced enrolment in August 2015 at Women and Newborn Hospital of University Teaching Hospital in Lusaka, Zambia. Women at less than 20weeks of pregnancy who were enrolled between August 17, 2015, and August 31, 2017, and underwent ultrasonography examination were included in the present analysis. The primary outcome was the difference between ultrasonography- and LMP-based estimated gestational age. Associations between baseline predictors and outcomes were assessed using simple regression. The proportion of preterm deliveries using LMP- and ultrasonography-derived gestational dating was calculated using Kaplan-Meier analysis. The analysis included 942 women. The discrepancy between estimating gestational age using ultrasonography and LMP increased with greater gestational age at presentation and among patients with no history of preterm delivery. In a Kaplan-Meier analysis of 692 deliveries, 140 (20.2%, 95% confidence interval [CI] 17.7-23.0) and 79 (11.4%, 95% CI 9.6-13.6) deliveries were classified as preterm by LMP and ultrasonography estimates, respectively. Taking ultrasonography as a standard, a bias was observed in LMP-based gestational age estimates, which increased with advancing gestation at presentation. This resulted in misclassification of term deliveries as preterm.

Validity of gestational age estimates by last menstrual period and neonatal examination compared to ultrasound in Vietnam

BackgroundAccurate estimation of gestational age is important for both clinical and public health purposes. Estimates of gestational age using fetal ultrasound measurements are considered most accurate but are frequently unavailable in low- and middle-income countries. The objective of this study was to assess the validity of last menstrual period and Farr neonatal examination estimates of gestational age, compared to ultrasound estimates, in a large cohort of women in Vietnam.MethodsData for this analysis come from a randomized, placebo-controlled micronutrient supplementation trial in Vietnam. We analyzed 912 women with ultrasound and prospectively-collected last menstrual period estimates of gestational age and 685 women with ultrasound and Farr estimates of gestational age. We used the Wilcoxon signed rank sum test to assess differences in gestational age estimated by last menstrual period or Farr examination compared to ultrasound and computed the intraclass correlation coefficient (ICC) and concordance correlation coefficient (CCC) to quantify agreement between methods. We computed the Kappa coefficient (κ) to quantify agreement in preterm, term and post-term classification.ResultsThe median gestational age estimated by ultrasound was 273.9 days. Gestational age was slightly overestimated by last menstrual period (median 276.0 days, P < 0.001) and more greatly overestimated by Farr examination (median 286.7 days, P < 0.001). Gestational age estimates by last menstrual period and ultrasound were moderately correlated (ICC = 0.78) and concordant (CCC = 0.63), whereas gestational age estimates by Farr examination and ultrasound were weakly correlated (ICC = 0.26) and concordant (CCC = 0.05). Last menstrual period and ultrasound estimates of gestational age were within ± 14 days for 88.4% of women; Farr and ultrasound estimates were within ± 14 days for 55.8% of women. Last menstrual period and ultrasound estimates of gestational age had higher agreement in term classification (κ = 0.41) than Farr and ultrasound (κ = 0.05).ConclusionIn this study of women in Vietnam, we found last menstrual period provided a more accurate estimate of gestational age than the Farr examination when compared to ultrasound. These findings provide useful information about the utility and accuracy of different methods to estimate gestational age and suggest last menstrual period may be preferred over Farr examination in settings where ultrasound is unavailable.Trial registrationThe trial was registered at ClinicalTrials.Gov as NCT01665378 on August 13, 2012.

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

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

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.

English

The expected date of delivery is of paramount importance to pregnant woman, her relatives, and treating doctor. It is useful for arranging help required and to take appropriate obstetric decisions. This study was aimed to find more accurate method to know Expected date of delivery. This was prospective study done on 800 new cases coming to Antenatal Outpatient clinic. A total of 318 cases were included in analysis. Rest of them were excluded for various reasons. In the patients selected Expected date was calculated according to Naegle’s rule calculation (L.M.P. date +280days) and by measuring femur length and biparietal diameter of fetal head measured on ultrasound scan and using Hadlock charts already available on ultrasound machines. Actual date when these patients went in labour spontaneously was noted eventually. Accuracy rates for ultrasound scan and menstrual period estimates of date of delivery were calculated as the percentage estimates accurate to within a given number of days. Significance tests and confidence intervals for differences in these paired rates were calculated. The cases where the estimated dates of delivery disagree are termed discrepant. For 33 patients the estimated dates of delivery from the two methods were identical and in 27 of these cases they were exactly correct. The percentages of the 285 discrepant cases in which the scan gave closer prediction of the date of delivery than the last menstrual period. It can be concluded that all persons involved with antenatal care, may be doctors or the patients and relatives should rely the estimated date of delivery derived from ultrasound scan and ignore the one calculated by Naegle’s rule once the satisfactory scan has been obtained. The study was undertaken to compare and know the more accurate and reliable method to calculate Expected Date of Delivery for the pregnant women coming to Antenatal Outpatient department. Total 800 women were included in the study initially coming from different parts of the district. Out of the above only 318 women were taken for analysis and the rest were excluded for various reasons.

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.

A comparison of LMP‐based and ultrasound‐based estimates of gestational age using linked California livebirth and prenatal screening records

Although early ultrasound (<20 weeks' gestation) systematically underestimates the gestational age of smaller fetuses by approximately 1-2 days, this bias is relatively small compared with the large error introduced by last menstrual period (LMP) estimates of gestation, as evidenced by the number of implausible birthweight-for-gestational age. To characterise this misclassification, we compared gestational age estimates based on LMP from California birth certificates with those based on early ultrasound from a California linked Statewide Expanded Alpha-fetoprotein Screening Program (XAFP). The final sample comprised 165 908 women. Birthweight distributions were plotted by gestational age; sensitivity and positive predictive value for preterm rates according to LMP were calculated using ultrasound as the 'gold standard'. For gestational ages 20-27 and 28-31 weeks, the LMP-based birthweight distributions were bimodal, whereas the ultrasound-based distributions were unimodal, but had long right tails. At 32-36 weeks, the LMP distribution was wider, flatter, and shifted to the right, compared with the ultrasound distribution. LMP vs. ultrasound estimates were, respectively, 8.7% vs. 7.9% preterm (<37 weeks), 81.2% vs. 91.0% term (37-41 weeks), and 10.1% vs. 1.1% post-term (>or=42 weeks). The sensitivity of the LMP-based preterm birth estimate was 64.3%, and the positive predictive value was 58.7%. Overall, 17.2% of the records had estimates with an absolute difference of >14 days. The groups most likely to have inconsistent gestational age estimates included African American and Hispanic women, younger and less-educated women, and those who entered prenatal care after the second month of pregnancy. In conclusion, we found substantial misclassification of LMP-based gestational age. The 2003 revised US Standard Certificate of Live Birth includes a new gestational age item, the obstetric estimate. It will be important to assess whether this estimate addresses the problems presented by LMP-based gestational age.

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.

Comparison of Gestational Age Classifications: Date of Last Menstrual Period vs. Clinical Estimate

The purpose was to compare the two different measures of gestational age currently used on birth certificates (the duration of pregnancy based on the date of last menstrual period [LMP] and the clinical estimate [CE] as related to health status indicators. We contrasted these measures by race/ethnicity. NCHS natality files for 2000-2002 were used, selecting cases of single live birth to U.S. resident mothers with both LMP and CE gestational age information. Approximately 75% of the records had valid LMP and CE values and for approximately one-half of these, the LMP and CE values did not exactly agree. Overall and for each race and ethnic group, the LMP measures resulted in higher proportions of very preterm, preterm, postterm and SGA births. CE value provided preterm rates of 7.9% and for LMP, 9.9%. The odds ratio of preterm birth for African-Americans using the CE measure was 1.78 [95% Cl 1.77-1.79]. The odds ratio using LMP was 1.93 [95% Cl 1.92-1.94]. Whites were the referent population. Different measures of gestational age result in different overall and race-specific rates of very preterm, preterm, postterm, and SGA births. These findings indicate that substituting or combining these measures may have consequences.

Preterm birth in Sweden 1973–2001: Rate, subgroups, and effect of changing patterns in multiple births, maternal age, and smoking

The objectives of this report are to evaluate changes in the preterm birth rate in Sweden 1973-2001. Furthermore, describe the proportion of spontaneous and indicated preterm births and assess risk factors for the subgroups of preterm birth during the period from 1991 to 2001. A population-based register study of all births occurring in Sweden from 1973 to 2001 registered in the Swedish Medical Birth Register was designed. The analysis of subgroups was restricted to the period 1991-2001. Gestational age was calculated using last menstrual period and best estimate. Odds ratio for preterm birth related to risk factors was calculated for the subgroups' spontaneous and indicated preterm birth. After an increase in the beginning of the 1980s, the preterm birth rate has decreased from 6.3% in 1984 to 5.6% in 2001 (P < 0.0001). The proportion of multiple births born preterm of the total birth rate increased from 0.34% in 1973 to 0.71% in 2001 (P < 0.0001). Spontaneous preterm births account for 55.2% and iatrogenic preterm births for 20.2% of all preterm births. The strongest association with maternal smoking in early pregnancy was found at gestational age <28 weeks and spontaneous preterm birth [odds ratio (OR) smoking versus no smoking: 1.55, 95% confidence intervals (CI): 1.42-1.69]. The strongest association for maternal age was found between gestational age <28 weeks and indicated preterm birth (OR 5-year increase: 1.34, 95% CI: 1.21-1.47). The preterm birth rate in Sweden has decreased since the mid 1980s. The composition of different subtypes of preterm birth in a Scandinavian low-risk population seems to be similar to populations with higher incidence of preterm birth and perinatal infections.

Preterm birth in Sweden 1973-2001: Rate, subgroups, and effect of changing patterns in multiple births, maternal age, and smoking

Background. The objectives of this report are to evaluate changes in the preterm birth rate in Sweden 1973–2001. Furthermore, describe the proportion of spontaneous and indicated preterm births and assess risk factors for the subgroups of preterm birth during the period from 1991 to 2001. Methods. A population-based register study of all births occurring in Sweden from 1973 to 2001 registered in the Swedish Medical Birth Register was designed. The analysis of subgroups was restricted to the period 1991–2001. Gestational age was calculated using last menstrual period and best estimate. Odds ratio for preterm birth related to risk factors was calculated for the subgroups' spontaneous and indicated preterm birth. Results. After an increase in the beginning of the 1980s, the preterm birth rate has decreased from 6.3% in 1984 to 5.6% in 2001 (P < 0.0001). The proportion of multiple births born preterm of the total birth rate increased from 0.34% in 1973 to 0.71% in 2001 (P < 0.0001). Spontaneous preterm births account for 55.2% and iatrogenic preterm births for 20.2% of all preterm births. The strongest association with maternal smoking in early pregnancy was found at gestational age <28 weeks and spontaneous preterm birth [odds ratio (OR) smoking versus no smoking: 1.55, 95% confidence intervals (CI): 1.42–1.69]. The strongest association for maternal age was found between gestational age <28 weeks and indicated preterm birth (OR 5-year increase: 1.34, 95% CI: 1.21–1.47). Conclusions. The preterm birth rate in Sweden has decreased since the mid 1980s. The composition of different subtypes of preterm birth in a Scandinavian low-risk population seems to be similar to populations with higher incidence of preterm birth and perinatal infections.

Mid-trimester ultrasound prediction of gestational age: advantages and systematic errors.

To detect possible sources of bias in ultrasound prediction of gestational age. Using the Swedish Medical Birth Registry, 571 617 women were identified who were delivered between 1990 and 1997 and who had obtainable information on last menstrual period and expected date of delivery according to ultrasound. Male fetuses were more likely than females to be judged older than the last menstrual period date suggested at early fetometry. The estimated magnitude of the systematic error by infant gender corresponded to 1.5 days. Similarly, the fetuses of young women, multiparous women, smokers and women with low educational level were at increased risk of being smaller than expected at ultrasound examination in early pregnancy. A strong association was seen between adjustments of expected date of delivery -7 days or more and small-for-gestational age according to ultrasound at birth. Compared to singleton pregnancies, twin pregnancies were more likely to be judged more progressed at ultrasound fetometry than the last menstrual period date suggested. Compared to last menstrual period estimates, routine ultrasound measurements to predict date of delivery are comparatively reliable but systematic errors are inherent in the method. The erroneous adjusted dates may be due to incorrect measurements or systematic bias (e.g. gender), but they are also likely to reflect early growth restriction (e.g. in the case of maternal smoking and small-for-gestational age). Further studies are needed to investigate whether the systematic errors in ultrasound prediction of gestational age could lead to suboptimal obstetric management in adjusted pregnancies.

Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination

Objective: The purpose of this study was to evaluate the accuracy of algorithms for the assignment of gestational age with the use of the last menstrual period and early ultrasound information. Study Design: Gestational age estimates that are based on last menstrual period, ultrasound scanning, or their combination were compared among women who attended prenatal care clinics in central North Carolina (n = 3655) by an evaluation of digit preference in the last menstrual period dates and a comparison of mean gestational age, preterm and postterm categories with the use of κ statistics, difference between actual and expected delivery date, and birth weight among subgroups with discrepant assignments. Results: Last menstrual period reports show digit preference, assign gestation 2.8 days longer on average than ultrasound scanning, yield substantially more postterm births (12.1% vs 3.4%), and predict delivery among term births less accurately. Misclassification of births as postterm was more common in younger women, those of nonoptimal prepregnancy body weight, cigarette smokers, and women who reported last menstrual period using preferred dates of the month. Conclusion: Last menstrual period estimates of the duration of gestation are subject to both random error and a systematic tendency to overstate the duration of gestation, most likely because of delayed ovulation. (Am J Obstet Gynecol 2002;187:1660-6.)

How does early ultrasound scan estimation of gestational age lead to higher rates of preterm birth?

OBJECTIVE: Early ultrasound scanning estimation of gestational age is known to increase the reported preterm delivery rate (<37 completed weeks) compared with estimation by date of the last normal menstrual period, but it is unclear how this systematic difference arises. STUDY DESIGN: This study was a hospital-based study of 44,623 women who delivered a live-born or stillborn infant between January 1, 1978, and March 31, 1996, and who had both last normal menstrual period-based and early (usually at 16-18 weeks) ultrasound scan-based gestational age estimates. Cross-classification of the 2 estimates by completed weeks was used to examine the direction and magnitude of the differences between them and to compare the resulting classifications of preterm birth. RESULTS: The early ultrasound scan-based gestational age distribution was shifted uniformly to the left (ie, lower gestational age) relative to the last normal menstrual period gestational age distribution; the early ultrasound scan-based preterm delivery rate was 9.1%, which was 19.5% (n = 659 births) higher than the 7.6% rate by last normal menstrual period (P <.0001). The last normal menstrual period estimate exceeded the early ultrasound scan estimate far more often than the reverse, up to and including early ultrasound scan estimates of 40 weeks. No concentration of 4-week discrepancies was observed in either direction, as would be expected with random or systematic errors in recall of the last normal menstrual period. The absolute number of births at 37 to 39 weeks of gestation (by last normal menstrual period) that were reclassified as preterm (n = 1206 births) was much higher than the number of preterm births at 34 to 36 weeks of gestation that were reclassified as term (n = 581 births). The net increase of 625 preterm births (from 581 to 1206 births) that resulted from reclassification of births at 37 to 39 last normal menstrual period weeks accounted for 95% of the total 659-birth increase in early ultrasound scan-based preterm births at all last normal menstrual period gestational ages. CONCLUSION: Early ultrasound scanning reduces the gestational age estimate across the entire gestational age range; early ultrasound scan-based reclassification of gestational age results in a substantial increase in the prevalence of preterm births. Small downward reclassifications exceed upward reclassifications of similar magnitude, which is consistent with previous reports that delayed (>14 days) ovulation is more frequent than early (<14 days) ovulation. (Am J Obstet Gynecol 2002;186:433-7.)

Seasonality in Conception of Births and Influence on Late Initiation of Prenatal Care

In Brief Objective To determine whether there is a summer peak in conception of births to adolescents (up to 17 years) compared with older teenagers (18–19 years) and adults (20–29 years), and to assess the influence of season of conception on late initiation of prenatal care. Methods We analyzed 1,178,607 singleton births to women aged 29 years and younger in Texas between 1994 and 1998. Dates of conception were estimated using last menstrual period and clinical estimates of gestation. Proportions of births conceived per month were assessed for seasonal patterns. Proportions of births with late initiation of prenatal care were also compared by month of conception. The outcomes were further stratified by sociodemographic variables. Results There was a consistent summer trough (7.5% in August) and year-end peak (9.1% in December) in conception of births to adolescents (P < .001), a pattern similar to that of older teenagers and adults. Among the adolescents, students and non-Hispanic women giving birth presented a secondary early summer peak (8.8% each in May and June) in their conceptions. There was a modest bimodal effect of season of conception on initiation of prenatal care in all age groups. Adolescent conceptions in April–May and September–October were 14–18% and 6% significantly more likely to have late prenatal care compared with other months, respectively. Conclusion Adolescents giving birth in Texas were not more likely to conceive in the summer. They did present seasonal patterns of conception and late initiation of prenatal care similar to older women. Texas adolescents have a small year-end peak in conceptions resulting in birth and a bimodal pattern of late initiation of prenatal care, similar to older women.

Seasonality in conception of births and influence on late initiation of prenatal care

Objective: To determine whether there is a summer peak in conception of births to adolescents (up to 17 years) compared with older teenagers (18–19 years) and adults (20–29 years), and to assess the influence of season of conception on late initiation of prenatal care. Methods: We analyzed 1,178,607 singleton births to women aged 29 years and younger in Texas between 1994 and 1998. Dates of conception were estimated using last menstrual period and clinical estimates of gestation. Proportions of births conceived per month were assessed for seasonal patterns. Proportions of births with late initiation of prenatal care were also compared by month of conception. The outcomes were further stratified by sociodemographic variables. Results: There was a consistent summer trough (7.5% in August) and year-end peak (9.1% in December) in conception of births to adolescents ( P < .001), a pattern similar to that of older teenagers and adults. Among the adolescents, students and non-Hispanic women giving birth presented a secondary early summer peak (8.8% each in May and June) in their conceptions. There was a modest bimodal effect of season of conception on initiation of prenatal care in all age groups. Adolescent conceptions in April–May and September–October were 14–18% and 6% significantly more likely to have late prenatal care compared with other months, respectively. Conclusion: Adolescents giving birth in Texas were not more likely to conceive in the summer. They did present seasonal patterns of conception and late initiation of prenatal care similar to older women.

Fetal outcome in pregnancies defined as post-term according to the last menstrual period estimate, but not according to the ultrasound estimate.

To study the risk of adverse fetal outcome in fetuses that were post-term according to the last menstrual period estimate but not according to the ultrasound estimate. A total of 11,510 women with singleton pregnancies, reliable last menstrual period and delivery after 37 weeks were divided into four groups: women who delivered at term, i.e. within 259-295 days according to both the ultrasound and the last menstrual period estimate; women who delivered post-term according to the last menstrual period estimate but not according to the ultrasound estimate; women who delivered post-term according to the ultrasound estimate but not according to the last menstrual period estimate; and women who delivered post-term according to both the ultrasound and the last menstrual period estimates. Stepwise logistic regression was used to test whether the risk of Apgar score of < 7 after 5 min and transfer to the neonatal intensive care unit increased in any of the post-term groups. There was no significant difference in mortality between the term group and the three study groups. There was no significant increase in the risk for Apgar score of < 7 after 5 min or transfer to the neonatal intensive care unit for pregnancies that were defined as post-term according to the last menstrual period estimate but not according to the ultrasound estimate. There was, however, an increased risk for Apgar score of < 7 after 5 min in the group that was post-term according to the ultrasound estimate but not according to the last menstrual period estimate. There was also an increased risk for transfer to the neonatal intensive care unit in the group that was post-term according to both estimates. The effect of ultrasound in changing the estimated day of delivery to a later date leading to pregnancies becoming post-term according to the last menstrual period estimate but not according to the ultrasound estimate does not have any adverse consequences for the fetal outcome. However, there seems to be an increased risk for adverse consequences for pregnancies that are post-term according to the ultrasound estimate.

Fetal outcome when the ultrasound estimate of the day of delivery is more than 14 days later than the last menstrual period estimate.

To evaluate the effect on fetal outcome of changing the estimated day of delivery as calculated according to ultrasound measurements more than 14 days later than the day estimated according to the last menstrual period. A non-selected population comprising 15,241 women was evaluated. A study group (the day of delivery based on the ultrasound estimate being changed to more than 14 days later than the estimate based on the last menstrual period) and a control group (the two estimates being within 7 days of each other) were compared regarding various parameters concerning fetal outcome. Changing the estimated day of delivery, based on the ultrasound evaluation, to a date 14 days later than the day of delivery as estimated according to the last menstrual period did not influence the risk of abortion, perinatal death or transferral to the neonatal intensive care unit. There was a difference of 3 days in the accuracy of the prediction of day of delivery between the two groups. There was a greater number of infants with a birth weight below 2500 g in the study group, but no difference was found between the groups in the number of infants with a birth weight < 2 SD from the mean according to the ultrasound estimate. There was no indication of any adverse consequence of the routine scan and change of estimated day of delivery among 15,000 pregnancies in a non-selected population.

Gestational Age Assessment in Preterm Neonates Weighing Less Than 1500 Grams

Postnatal assessment of gestational age in preterm neonates traditionally has been performed using the methods of Dubowitz and Ballard. This study was designed to determine the accuracy of these methods in a sample of very low birth weight preterm neonates. Dubowitz and Ballard examinations were done on 110 preterm neonates within the first 72 hours of life by a neonatologist masked to the gestational age assessed antenatally. Mean birth weight was 1066 ± 256 g (SD). These data were compared with gestational age assessments using last menstrual period and best obstetric estimate calculated by an obstetrician unaware of the neonatal examination. Mean gestational age using last menstrual period was 28.3±2.9 weeks. Mean differences between last menstrual period and Dubowitz/Ballard were -2.8±2.1 weeks and -2.6±2.2 weeks, respectively. Results using best obstetric estimate were similar. An ophthalmologist examined lens vessels of 89 neonates. A similar pattern toward overestimation of gestational age interval by Dubowitz/Ballard was seen at each lens vessel grade. The Dubowitz and Ballard examinations are inaccurate methods of assessing gestational age in preterm neonates with birth weights less than 1500 g.