Determining gestational age for public health care users in Brazil: comparison of methods and algorithm creation

Abstract

BackgroundA valid, accurate method for determining gestational age (GA) is crucial in classifying early and late prematurity, and it is a relevant issue in perinatology. This study aimed at assessing the validity of different measures for approximating GA, and it provides an insight into the development of algorithms that can be adopted in places with similar characteristics to Brazil. A follow-up study was carried out in two cities in southeast Brazil. Participants were interviewed in the first trimester of pregnancy and in the postpartum period, with a final sample of 1483 participants after exclusions. The distribution of GA estimates at birth using ultrasound (US) at 21–28 weeks, US at 29+ weeks, last menstrual period (LMP), and the Capurro method were compared with GA estimates at birth using the reference US (at 7–20 weeks of gestation). Kappa, sensitivity, and specificity tests were calculated for preterm (<37 weeks of gestation) and post-term (>=42 weeks) birth rates. The difference in days in the GA estimates between the reference US and the LMP and between the reference US and the Capurro method were evaluated in terms of maternal and infant characteristics, respectively.ResultsFor prematurity, US at 21–28 weeks had the highest sensitivity (0.84) and the Capurro method the highest specificity (0.97). For postmaturity, US at 21–28 weeks and the Capurro method had a very high sensitivity (0.98). All methods of GA estimation had a very low specificity (≤0.50) for postmaturity. GA estimates at birth with the algorithm and the reference US produced very similar results, with a preterm birth rate of 12.5%.ConclusionsIn countries such as Brazil, where there is less accurate information about the LMP and lower coverage of early obstetric US examinations, we recommend the development of algorithms that enable the use of available information using methodological strategies to reduce the chance of errors with GA. Thus, this study calls into attention the care needed when comparing preterm birth rates of different localities if they are calculated using different methods.

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

“…In the Nascer no Brasil (Birth in Brazil) study conducted at the national level, regarding the estimate of preterm birth based on last menstrual period compared to early obstetric ultrasonography, 69.4% sensitivity was observed for pregnant women treated in the public sector and 72% sensitivity was observed for those treated in the private sector. The present results are also consistent with other Brazilian studies which demonstrated that the use of LMP overestimates the rate of preterm birth by about 10% to 34% 4,5 while considerably underestimating the post-term birth rate 5 . However, a study conducted in Canada demonstrated that the use of LMP underestimates the preterm birth, in contrast to what was observed here 1 .…”

“…It is influenced by retarded ovulation, bleeding at the beginning of pregnancy, use of an oral contraceptive after the perception of amenorrhea, short birth spacing and memory bias 3,4 . In addition, errors in gestational age estimate based on LMP are greater in populations of lower educational levels 5 .…”

“…Due to the still low availability of obstetric ultrasonography in epidemiological studies, it is important to carry out studies for LMP validation. Studies have demonstrated that LMP tends to underestimate or overestimate the rate of preterm birth and to overestimate the rate of postterm birth 1,5,6 . However, most of the available studies have been conducted in high-income countries 1,2 , with little information available for low and middle-income countries 5 , in which errors of gestational age classification based on LMP must be greater.…”

Prevalência de nascimentos pré-termo por peso ao nascer: revisão sistemática

“…12 Two Brazilian studies present conflicting visions of this topic. A prospective study in two cities in the Southeast of public health care system -Sistema Único de Saúde (SUS) users 20 showed that, compared with results obtained by ultrasound (US) up to 20 weeks, the date of the last menstrual period (after excluding outliers) had a sensitivity of 71.0% and accuracy of 94.0%, estimating the prevalence at 14.0% compared with 12.5% according to US. The authors considered the US as the gold standard, without discussing the quality of the examination and mentioned that in one of the two municipalities, they were performed by a health care professional connected to the research team.…”

Determinação da idade gestacional com base em informações do estudo Nascer no Brasil

“…In 2011, this information came to be collected in a disaggregated way, according to weeks of gestation, with the main calculation method being the date of the last menstrual period (LMP) 2 , and making possible the recording of gestational age information based on other assessment methods (physical examination or ultrasound imaging) 2 . However, these methods have different levels of validity 3,4,5,6 , making the assessment of gestational age in the country more difficult.…”