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Table 2 Validity of LMP compared to CRL for gestational age estimation, overall and by parity, rural Bangladesh, 2008–2009

From: A home calendar and recall method of last menstrual period for estimating gestational age in rural Bangladesh: a validation study

  All Nulliparous Parous
Ultrasound visit (n = 353) (n = 134) (n = 219)
Gestational agea
 Last menstrual period, days 76.1 (12.5) 78.8 (12.8) 74.4 (12.1)
 Crown-rump length, days 73.3 (12.9) 74.6 (12.7) 72.5 (13.0)
 LMP-CRL, days 2.8 (10.8) 4.2 (10.0) 1.9 (11.2)
Convergent validityb
 Pearson’s correlation coefficient 0.63 0.69 0.61
 Bias Correction Factor 0.98 0.95 0.99
 Lin’s concordance correlation coefficient (95 % CI) 0.63 (0.56, 0.69) 0.66 (0.56, 0.75) 0.60 (0.52, 0.68)
Live birth (n = 332) (n = 127) (n = 205)
Gestational agea
 Last menstrual period, days 276.2 (18.1) 275.9 (17.7) 276.5 (18.4)
 Crown-rump length, days 273.4 (14.2) 271.6 (13.6) 274.6 (14.5)
 LMP-CRL, days 2.8 (10.7) 4.3 (10.0) 1.9 (11.0)
Convergent validityb
 Pearson’s correlation coefficient 0.81 0.83 0.80
 Bias correction factor 0.96 0.93 0.97
 Lin’s concordance correlation coefficient (95 % CI) 0.77 (0.73, 0.81) 0.77 (0.71, 0.83) 0.77 (0.72, 0.83)
Validity of classifying preterm
 Prevalence of preterm by LMP, % (n) 10.8 (36) 13.4 (17) 9.3 (19)
 Prevalence of preterm by CRL, % (n) 8.7 (29) 11.0 (14) 7.3 (15)
 Sensitivity, % 86.2 92.9 80.0
 Specificity, % 96.4 96.5 96.3
 Positive predictive value, % 69.4 76.5 63.1
 Kappa 0.74 0.82 0.68
Validity of classifying post-term
 Prevalence of post-term by LMP, % (n) 14.2 (47) 15.0 (19) 13.7 (28)
 Prevalence of post-term by CRL, % (n) 3.6 (12) 1.6 (2) 4.9 (10)
 Sensitivity, % 66.7 87.2 60.0
 Specificity, % 88.8 87.4 89.7
 Positive predictive value, % 18.2 11.1 23.1
 Kappa 0.24 0.18 0.28
  1. Preterm is <259 days, term is 259-293 days, and post-term is >293 days gestational age by ultrasound; the Hadlock equation is used for CRL estimate of gestational age
  2. LMP first day of the last menstrual period, CRL crown-rump length
  3. aData presented as mean (SD)
  4. bIn validation analysis: Pearson’s coefficient is a measure of precision; the bias correction factor is a measure of accuracy; and Lin’s concordance correlation coefficient is a measure of reproducibility (accounting for precision and accuracy in the same estimate). Perfect correlation/concordance for each measure = 1