382
Reply: Legislation of embryo
transfer affected the
denominator, not the numerator!
Sir,
We read with interest the Letter to the Editor by Scholten et al., (2013)
regarding our paper (De Neubourg et al., 2013). We do not agree with
their comments and disagree with the data they use to build their case.
Scholten et al. state that the absolute numbers of multiple embryo
transfers showed a slight reduction from 9671 in 2002 to 9555 in 2010.
However, in our calculation there were 9614 multiple embryo transfers in
2002 and 9371 in 2010 when analyzing the raw data without extrapolations.
Furthermore, the absolute number of twin pregnancies was not 447 in
2002 and 407 in 2010, as stated by Scholten et al. but 429 in 2002 and 379
in 2010, when analyzing our raw data.
In conclusion, the new Belgian legislation indeed resulted in a decrease
in the absolute number of multiple embryo transfers and of twin pregnancies and in a substantial increase in the number of assisted reproductive
technology (ART) cycles. In fact, both numerator [reduction of the
number (N) of multiple embryo transfers and of N of twin pregnancies]
and denominator (increase in N of ART cycles) were affected by the legislation. However, as incidence is defined as the number of events arising
in a population in a given time period, our conclusion is correct that the
new Belgian legislation resulted in a 50% reduction of the incidence of
multiple pregnancies. Given that access to ART treatment was improved,
an important increase in twin and multiple pregnancies could have been
anticipated if reimbursement of laboratory costs had not been coupled to
Letters to the Editor
a restriction in the number of embryos for transfer. Therefore, our conclusion and title remains valid.
We agree with Scholten et al. that it is important to calculate ART
results and reproductive outcome parameters per patient rather than
per cycle, as mentioned in the discussion of our paper (see future
focus of De Neubourg et al., 2013). Since 2009, the Belgian registration
system has been adapted to allow such a patient-based calculation, which
will also allow one to calculate prospectively the time to pregnancy per
patient (see Materials and Methods of De Neubourg et al., 2013).
Reference
De Neubourg D, Bogaerts K, Wyns C, Albert A, Camus M, Candeur M,
Degueldre M, Delbaere A, Delvigne A, De Sutter P et al. The history of
Belgian assisted reproduction technology cycle registration and control:
a case study in reducing the incidence of multiple pregnancy. Hum
Reprod 2013;28:2709 – 2719.
Scholten I, Kamphuis E, Mol BWJ. Legislation of embryo transfer affected the
denominator, not the numerator. Hum Reprod 2013;28. doi:10.1093/
humrep/det415.
Diane De Neubourg1,2,*, Kris Bogaerts3 and Thomas D’Hooghe1,2
LUFC, Department of Obstetrics and Gynaecology, University Hospitals Leuven,
Leuven, Belgium
2
Department of Development and Regeneration, KU Leuven, Leuven, Belgium
3
I-BioStat, Katholieke Universiteit Leuven and Universiteit Hasselt, Leuven, Belgium
1
*Correspondence address. E-mail: [email protected]
doi:10.1093/humrep/det416
Advanced Access publication on November 25, 2013