First-trimester Down syndrome screening following assisted conception

19 12 2013

To the Editor:

We would like to comment on the article written by Dr. Bellver and colleagues (1) regarding the need for adjustments of first-trimester Down syndrome screening parameters following assisted conception. Although we greatly appreciate their work, which confirms earlier data in the field, we would like to issue some additional remarks.

The Bellver et al. study suggests a reduced maternal serum pregnancy-associated plasma protein A (PAPP-A) and increased false positive rates (FPR) in singleton pregnancies achieved by in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), compared with naturally conceived pregnancies. However, the latter showed to be significant when including only ICSI cycles using non-donor oocytes. The authors discuss several other groups according mode of conception (IUI with partner or donor sperm, IVF, non-donor versus donor oocytes, fresh versus frozen embryo transfer), which veils the main message of the article, namely that (at least in their cohort) only in ICSI non-donor cycles serum PAPP-A level at first-trimester Down screening is significantly different from that seen in natural pregnancies. In their manuscript the authors describe a « diminished » PAPP-A level, even in cases where these levels are not significantly different, which is confusing.

Although the authors state that no significant differences were observed between the used laboratory techniques, the fact that dosages and calculations were performed with two different technologies during two successive periods warrants caution when interpreting the combined results.

The authors mention some interesting data relating to the ovarian stimulation protocol and its influence on the first-trimester Down screening biochemical markers. However, some details lack, such as the doses of gonadotropins/hormones used. Also, the finding that cycles in which only FSH was administered presented a significant reduction in PAPP-A MoM values, whereas this was not the case for FSH+LH regimens, needs additional discussion. Of course, we agree with the authors on the hypothesis that ovarian stimulation may alter first-trimester biochemical screening parameters, since we found that decreased PAPP-A levels following IVF or ICSI were strongly correlated with the estradiol level at ovulation triggering (2). However, we tend to disagree with the hypothesis that the ICSI technique adds an insult to the zona pellucida (ZP) of the oocytes, which in turn leads to altered serum PAPP-A levels by the placenta. If so, this effect should also be found in donor ICSI cycles. Another hypothesis might be that ICSI alters the constitution of the cytoplasm of the oocyte (and further downstream the origin of the placenta), rather than the ZP solely. Indeed, the placenta does not originate from the zona pellucida, but from the trophectoderm of the blastocyst.

Finally, we agree with the authors that studies investigating first-trimester biochemical markers should be performed in the scope of their correlation with complications in ART pregnancies.

Frauke Vanden Meerschaut, M.D., Ph.D.1, Claude Giorgetti, Ph.D.2, Petra De Sutter, M.D., Ph.D.1
1Centre for Reproductive Medicine, University Hospital Ghent, Belgium
2Institute of Reproductive Medicine, Marseille, France

References

1. Bellver J, Casanova C, Garrido N, Lara C, Remohi J, Pellicer A, et al. Additive effect of factors related to assisted conception on the reduction of maternal serum pregnancy-associated plasma protein A concentrations and the increased false-positive rates in first-trimester Down syndrome screening. Fertil Steril 2013;100:1314-20.

2. Giorgetti C, Vanden Meerschaut F, De Roo C, Saunier O, Quarello E, Hairion D, et al. Multivariate analysis identifies the estradiol level at ovulation triggering as an independent predictor of the first trimester pregnancy-associated plasma protein-A level in IVF/ICSI pregnancies. Hum Reprod 2013;28:2636-42.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2013.12.036

The authors respond:

Our paper (1) not only tries to show our personal experience but also performs a review of the current literature on first-trimester Down syndrome (DS) screening in assisted conception. As summarized in Table 1, most previous series (and particularly the most recent ones with larger sample sizes) show a significant reduction of serum pregnancy-associated plasma protein A (PAPP-A) concentrations in pregnancies achieved by IVF and especially by ICSI. In our population, both IVF and ICSI pregnancies showed reduced maternal serum PAPP-A and increased false-positive rates in DS screening, but were significant only in ICSI cycles. However, the sample size of our IVF cycles was quite small (n=328) compared to our ICSI cycles (n=1,364) and the most recent studies on IVF (n=2,115 in the largest [2]). As the latter showed significantly decreased PAPP-A levels in IVF cycles, we can infer that the reduction seen in our IVF group did not reach statistical significance probably due to the smaller sample size. For this reason, we also included the IVF cycles in our recommendation to perform adjustment of the PAPP-A levels in addition to ICSI cycles, in both cases when using own oocytes (non-donor cycles). In our opinion, the important message is that no adjustments are needed for the other low-rank assisted reproduction techniques or for free β-hCG levels.

Regarding the two laboratory techniques employed, caution was taken to check first the lack of differences between them before combining the whole set of biochemical data, as in previous publications (3).

With respect to the type of gonadotropins used, we observed a reduction of serum PAPP-A concentrations in cycles in which only FSH was used for ovarian stimulation, but we have not found any reasonable explanation for it. On the other hand, we found that total doses of gonadotropins administered did not correlate with PAPP-A MoM values and only marginally with free β-hCG MoM values (r= 0.082; p = 0.027). So, it seems that the influence of gonadotropin doses on serum PAPP-A concentrations is lacking.

Concerning the effect of the ICSI technique on PAPP-A results and the theory suggested by our colleagues about the alteration of the constitution of the cytoplasm of the oocyte after ICSI, we fully agree that different unknown mechanisms may be responsible for the results obtained. But, there is no doubt that in pregnancies achieved by ICSI serum, PAPP-A concentrations are more affected than in those achieved by IVF, and that the main difference between ICSI and IVF is the different degree of manipulation of the oocyte in the IVF laboratory, especially in our setting in which ICSI is performed more frequently than IVF, even in the absence of a severe male factor. Obviously, further studies are needed to explore in depth the mechanisms involved.

José Bellver, M.D. and Vicente Serra, M.D.
Instituto Valenciano de Infertilidad, Universidad de Valencia, Valencia, Spain

References

1. Bellver J, Casanova C, Garrido N, Lara C, Remohí J, Pellicer A, et al. Additive effect of factors related to assisted conception on the reduction of maternal serum pregnancy-associated plasma protein A concentrations and the increased false-positive rates in first-trimester Down syndrome screening. Fertil Steril 2013;100:1314-20.

2. Kagan KO, Wright D, Spencer K, Molina FS, Nikolaides KH. First trimester screening for trisomy 21 by free beta-human chorionic gonadotropin and pregnancy-associated plasma protein A: impact of maternal and pregnancy characteristics. Ultrasound Obstet Gynecol;2008;31:493–502.

3. Gjerris AC, Loft A, Pinborg A, Christiansen M, Tabor A. First-trimester screening markers are altered in pregnancies conceived after IVF/ICSI. Ultrasound Obstet Gynecol;2009;33:8-17.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2013.12.037

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