DOI: 10.1002/pd.4228

CORRESPONDENCE

Comment on “On gestational weeks and maths”

With great interest, I read the position statement from the Aneuploidy Screening Committee on behalf of the Board of the International Society for Prenatal Diagnosis1, and am corroborating with the opinions about screening and diagnosis and the recommendations of the committee. At four places in the text, the term ‘gestational age(s)’ is used. How that age should be calculated is not described. In Table 1 and in the recommendations, one reads that 10 completed weeks equals ‘10 weeks 0 days to 10 weeks and 6 days’. However, the period between and including 100/7 and 106/7 weeks is the 11th week of gestation, and week 10 is completed when a gestational age of 100/7 weeks is reached. Defining completed gestational weeks the way the committee has done is an arithmetical aberration. It is less confusing to read that nuchal translucency should be measured and blood be sampled between and including

110/7 and 136/7 weeks and 100/7 and 136/7 weeks of gestation, respectively. How gestational age should be determined, for example, in aneuploidy screening, is – even when the day of oocyte retrieval and fertilization is known – apparently still open for discussion.2–4

Pieter Hummel Department of Obstetrics, Gynecology and Reproductive Medicine, Medical Center Alkmaar, Wilhelminalaan 12,1815 JD Alkmaar, the Netherlands Correspondence to: Pieter Hummel. E-mail: [email protected] Funding sources: None Conflicts of interest: None declared

REFERENCES 1. Benn P, Borell A, Chiu R, et al. Position statement from the Aneuploidy Screening Committee on behalf of the Board of the International Society for Prenatal Diagnosis. Prenat Diagn 2013;33:622–9. 2. Huttly WJ, Wald NJ. The estimation of gestational age of pregnancy for use in screening for Down syndrome using ultrasound measurements and embryo transfer date. Prenat Diagn 2012;32:1008-9. 3. Gjerris AC, Loft A, Pinborg A, et al. First-trimester screening in pregnancies conceived by assisted reproductive technology:

Prenatal Diagnosis 2013, 33, 1217

significance of gestational dating by oocyte retrieval or sonographic measurement of crown-rump length. Ultrasound Obstet Gynecol 2008;32:612–7. 4. Saltvedt S, Almström H, Kublickas M, et al. Ultrasound dating at 12–14 or 15–20 weeks of gestation? A prospective cross-validation of established dating formulae in a population of in-vitro fertilized pregnancies randomized to early or late dating scan. Ultrasound Obstet Gynecol 2004;24:42–50.

© 2013 John Wiley & Sons, Ltd.

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