Weight correction of MoM values: which method?

Abstract

Background: Adjusting maternal serum markers for maternal weight is considered to be a standard practice when screening for pregnancies associated with Down's syndrome. The choice of model for taking maternal weight into account is, however, rarely explicitly evaluated. Method: The relationship between the maternal serum markers afetoprotein (AFP), human chorionic gonadotropin (HCG) and unconjugated oestriol (uE3), determined with the Beckman Coulter access reagents and maternal weight was investigated in a cohort of 752 Belgian women being screened for pregnancy associated with Down's syndrome. Two different models (the log-linear equation and the linear-reciprocal equation) were used to determine the relationship between the serum markers and maternal weight. Results: A significant relationship between log 10 multiples of median (MoM) values and weight (kg) was obtained for all markers, and the log-linear model had higher coefficients of determination (r 2 ) when compared with the linear-reciprocal model. Weight correction with either method achieved the optimum effect that the correction factor for a woman with a population median weight of 65.5 kg was not significantly different from 1. Simulated weight-corrected MoM values with the two approaches were compared and variation was estimated. The mean difference between the weight-corrected MoM values calculated by the two methods was 7.8% (SD 4.3%) for AFP, 14.0% ( 4.4%) for HCG and 5.9% ( 3.2%) for uE3. This resulted in a difference in risk estimate of 1.66-5.34% for Down's syndrome owing to weight correction algorithm differences in women of median weight. Conclusion: The log-linear weight correction approach was shown to be marginally more effective by a goodness-of-fit analysis. Differences in weight-corrected MoM values estimated with the two approaches are highly significant (p,0.0001, Wilcoxon's paired sample test), but the effect on risk calculation was not significant. It was observed that the changes in risk became significant the more the MoM correction factors deviated from 1.

Comparison of the New PRC Software with the Established Algorithm of the FMF UK for the Detection of Trisomy 21 and 18/13

“…The main reason for the intolerably high false-positive rate for the biochemical trisomy 21 risk of PRC seems to be the fact that this software does not take into account maternal weight, nor are the so-called DoE values (that have been introduced instead of the internationally accepted MoM values) corrected for smoking, ethnicity, or IVF pregnancy status. Correction for maternal weight and ethnicity is generally regarded as essential in Down's syn- drome screening [12][13][14][15] , and the absence of a correction can lead to increased false-positive rates. Spencer et al [14] found that correction of the biochemical parameters for maternal weight resulted in a decrease in the falsepositive rate while maintaining the same detection rate.…”

Maternal Biochemical Serum Screening for Down Syndrome in Pregnancy With Human Immunodeficiency Virus Infection

“…Nevertheless, marker levels were stated in terms of multiple of the median (MoM) and thus were standardized on the most important confounding factors: gestational age, tobacco use, weight, and diabetes mellitus. 5,[12][13][14] Therefore, to adjust for confounding factors not taken into account in the calculation of this standardized rate, we matched cases and controls on geographic origin and fetal sex. We adopted a second-trimester double test based on serum AFP and total hCG levels.…”

Determination of the median levels of double and triple prenatal screening parameters in Adıyaman region

“…Çalışmamızda bölgemizdeki gebelerin nüfus kayıtlarının eksik olabildiği göz önüne alınarak formlar teslim alınırken gebenin gerçek doğum tarihi öğrenilip kaydedilmiştir. Bazı programlar gebenin ağırlığı olmadan da risk hesaplaması yapmaktadır, fakat gebenin ağırlığının düzeltme faktörü olarak kullanılıp hesaplanan risk analizleri daha güvenilirdir [17]. Bu yüzden çalışmamızda formlar laboratuvarda teslim alınırken eksik bilgiler kontrol edilmiş gebenin ağırlığı formda eksik ise tamamlanmıştır.…”