Original Article
Accurate reporting of expected delivery date by mothers 9 months after birth

https://doi.org/10.1016/j.jclinepi.2011.03.007Get rights and content

Abstract

Objective

To measure agreement between gestational age based on maternal report of expected date of delivery (EDD) 9 months after birth and gestational age at birth in routine hospital data. Furthermore, to examine whether sociodemographic and perinatal factors influenced agreement and whether disagreement affected classification of infants in preterm groups.

Study Design and Setting

The study used data on 8,058 singleton infants from the UK Millennium Cohort Study. Women were interviewed 9 months after birth and interviews were linked to routine hospital data. The infant’s date of birth and EDD were used to calculate gestational age in completed weeks.

Results

Agreement between maternal report and hospital data was 72% for exact number of weeks’ gestation and 94% for agreement within 1 week. Disagreement was associated with the infant not being firstborn, unplanned pregnancy, late or no antenatal care, and low socioeconomic status. Maternal report of gestational age resulted in slightly more children being classified as preterm (6.4%) than gestational age based on hospital data (6.1%). Agreement was found to be poor for postterm births.

Conclusion

Gestational age based on retrospective maternal reporting of EDD is reliable within 1 week or when used to assign infants to broad gestational groups.

Introduction

What is new?

Key findings

  1. For 94% of women, gestational age based on reported expected delivery date was within 1 week of hospital-based gestational age.

  2. 88% of children who were born preterm according to hospital data were also correctly identified as such by maternal report.

  3. Our study showed higher percentage of agreement and narrower limits of agreement than previous studies.

  4. Agreement varied with various indicators of social position. Investigators need to take this into account when basing a study on maternal report of gestational age.

Preterm birth is one of the most important determinants of neonatal and infant mortality [1], [2] and is strongly associated with child health and development [3]. As a result, gestational age is often considered in epidemiological studies as a pregnancy outcome, a risk factor for outcomes occurring in childhood and adulthood, or as a confounder.

Many research studies, such as maternity surveys [4], [5] and follow-up studies of preterm children [6], [7], rely on retrospective maternal report of gestational age when hospital records with results from ultrasound scan are unavailable or are too expensive or time-consuming to access. Asking women about gestational age or expected date of delivery (EDD) is often the simplest and cheapest way of obtaining the information, and it is therefore relevant to know how reliable maternal report of gestational age is.

In studies of the accuracy of maternal recall of perinatal events, it has generally been found that recall depends on the type of event, time since the event, and on how the question is formulated [8]. Some studies have looked at maternal recall of gestational age among recall of other perinatal factors [9], [10], [11], [12], [13], [14], but few have focused on gestational age alone and attempted to describe which factors influence the accuracy of recall of gestational age [15], [16].

Several studies have compared maternal report of gestational age with gestational age in medical records. High intraclass correlations (ICC) have been reported ranging from 0.64 [12] to 0.90 [14] and high kappa coefficients ranging from 0.56 [15] to 0.90 [14], but exact agreement in weeks has often been found to be low. In a recent Danish study of 678 women, the ICC was high (0.76), but only 42% of participating women reported exact gestational age, although 94% reported gestational age within 2 weeks of that recorded on the birth registration [15]. In a study of 208 women in Taiwan, the correlation coefficient was high (0.93), but only approximately two-thirds of women correctly reported exact gestational age [11].

The present study uses data on 8,058 women from the Millennium Cohort Study (MCS) to measure agreement between maternal report of gestational age 9 months after delivery and routine hospital data to describe which perinatal and sociodemographic factors influenced agreement and to examine how the potentially observed disagreement influenced classification of preterm birth.

Section snippets

Millennium Cohort Study

The MCS is a nationally representative longitudinal study of 18,818 infants born in the United Kingdom [17]. The study is based on a random two-stage sample drawn from child benefit registers of all infants born in England and Wales between September 2000 and August 2001, and in Scotland and Northern Ireland between November 2000 and January 2002, who were alive and living in the United Kingdom at the age of 9 months. Stratified sampling at electoral ward level, with oversampling of ethnic

Percentage disagreement

Agreement between MCS and hospital data was 72.2% for exact gestational age in completed weeks and 94.5% for agreement within 1 week either side (Table 2). Exact agreement varied by gestational age and was markedly lower for cases with values of 42 and 43 weeks in either data source (Table 3). In preterm infants, agreement within 1 week was 93.5% in infants born before week 32 and 85.2% in infants born between 32 and 36 completed weeks. In 98.0% of observations, the hospital data and maternal

Discussion

We compared gestational age estimated from maternal reporting of EDD 9 months after delivery with gestational age reported in routine hospital data in 8,058 singleton births. We found that 94% of women reported gestational age within 1 week of the gestational age in the hospital data. We found a clinically irrelevant mean difference of 0.04 weeks, corresponding to about a quarter of a day. Limits of agreement showed that 95% of differences fell within −1.6 and 1.7 weeks. This shows better

Conclusion

Our study suggests that gestation estimated from retrospective maternal reporting of EDD is accurate within 1 week of the gestation recorded in routine hospital data. For the assessment of exact gestation in weeks, there may be some misclassification arising from maternal report of EDD, although it is unclear whether this is because of inaccuracy in maternal reporting or ambiguities in the definition of EDD or gestational age. The high level of overall agreement that we observed suggests that

Acknowledgment

The study was supported by the Bupa Foundation, grant TBF-08-07.

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  • Cited by (0)

    Ethical approval: This article involves only secondary data analysis of the Millennium Cohort Study (MCS), which is available in the UK Data Archive, and therefore does not require ethical approval. Ethical approval for the MCS was granted from the Multicentre Research Ethics Committee..

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