Despite the theoretical benefit of a euploid embryo screened for aneuploidy by preimplantation genetic testing (PGT-A), the impact of PGT-A on first-trimester aneuploidy screening has not been accurately assessed. Most institutional guidelines recommend offering prenatal aneuploidy screening to all patients regardless of PGT-A testing. However, combined screening algorithms do not take into account that the embryo has been selected by PGT-A, and provide risk estimates for chromosomal abnormalities based primarily on maternal age. A recent study indicated that PGT-A screening does not reduce the likelihood of undergoing invasive prenatal diagnostic procedures when conventional prenatal screening is performed.

For this reason, a team from Dexeus Mujer, led by Dr Gabriela Palacios, conducted a study to evaluate the efficacy of combined first-trimester screening in pregnancies achieved through IVF with PGT-A. A total of 20,237 women undergoing prenatal follow-up at the study centre were included in the study. The women were divided into three groups: singleton pregnancies conceived through the transfer of a PGT-A-screened euploid embryo (n = 510); singleton pregnancies conceived through IVF without PGT-A (n = 3291); and singleton pregnancies conceived naturally (n = 16,436).

Conventional combined screening for pregnancies conceived through IVF with PGT-A had a specificity of 91%; sensitivity could not be calculated as there were no cases of foetal aneuploidy in this group. In 89.1% of pregnancies conceived through IVF with PGT-A at high risk for trisomy 21, 18 or 13, the result was associated with advanced maternal age (>35 years at the time of screening).

According to the results, the current combined screening strategy penalises pregnancies achieved through IVF with PGT-A, due to the high weight of maternal age in the a priori risk assessment, which is higher in these women. According to the authors, this strategy leads to unnecessary testing, with the consequent financial and emotional burden on patients. They therefore suggest abandoning the current strategy and establishing a new protocol for these patients, including an ultrasound scan at 11-14 weeks to measure nuchal translucency and additional ultrasound markers. Based on this result, they recommend a genetic counselling consultation to explore alternative screening or prenatal diagnostic options.