Letter to the Editor: The umbilical cord nomogram in 11-15 weeks of pregnancy

Keywords

Umbilical cord, nomogram, letter to the editor

Dear Editor, Dr Ozdemir and her colleagues aimed to establish umbilical cord nomogram of the first and early second trimester and to determine its relationship with other fetal biometric parameters in their study published in Perinatol. Journal 2007; 15(2): 51-55 (1). I would like bring the authors' some recommendations about the study methodology and data analysis process. 1.The authors gave information on study methodology as “this prospective cross - sectional study was performed in Department of Perinatology of Education and Research Hospital Between September 2003- March 2005, among 14000 pregnant women who underwent antenatal examination 128 consecutive pregnant women which is appropriate for our criteria included in our study”. The authors also stated the exlusion criteria for the subjects. It is not clear that if all eligible pregnant women of those 14.000 pregnant women were included the study or a random sample of pregnant women were included? If a sample of pregnant women were selected by a non-random way (even they have inclusion criteria and they don’t have exluison criteria), there would be selection bias in the study and the Authors should discuss it as a study restriction in the manuscript. In addition, it would be convenient using “cross - sectional study” term instead of using “prospective cross - sectional study” to define study type (2). 2. Gravida number distribution and parity number distribution were summarised with means and SDs in the manuscript. I suggest to the Authors to summarise the data with percentages (classifying data if necessary) since the distributions are quite heterogenic distributions. 3. It was stated in the manuscript that “the correlation between the umbilical cord and the age of the pregnant woman is shown by this formula: The cord diameter = 0. 69 x gestational week – 4.76 (r: 0.84.5)”. I think, the regression formula has been written incorrectly. Regression formula should have been written as: The cord diameter = 4.76+ gestational week x 0. 69 since gestational week and the cord diameter were positively correlated. In addition, there is no information about the statistical method related this formula in the study. The authors should give information about it in material method section as “simple lineer regression analysis was used to predict cord diameter”. 4. Correlation coefficient can be between (-1) and (+1). The correlation coefficients are not shown in the manuscript properly. Coefficients should be written (r=0.85) instead of (r=0.84.5), (r=0.77) instead of (r=77.4), (r=0.82) instead of (r=81.5).

References

1) Ozdemir A, Goynumer FG, Gokçen O, Yetim G, Karaaslan I..The Umbilical Cord Nomogram In 11-15 Weeks of Pregnancy.Perinatol. Journal 2007; 15(2): 51 - 55.
2) Hennekens HC, Buring JE..Analysis of Epidemiological Studies: Evaluating the Role of Bias.In: Mayrent SL (Ed).Epidemiology in Medicine.Boston-Little, Brown and Company:1987.

	File/Dsecription
	Table 1. The mean of umbilical cord diameter in 11-14 gestational weeks.