Spontaneous post-implantation embryo resolution: A new concept in embryo loss

Objective: To determine and compare in an ART population the chances of complete abortion rate, and of spontaneous post-implantation embryo resolution (SPIER) (partial re-absorption of 1 or more gestational sacs) in clinical pregnancies according to the original number of gestational sacs observed. Design: A prospective, on going study in a University-based private practice and in a public hospital facility ART units. Materials and Methods: We studied the outcome of 620 pregnancies originated from ART. There were 414 singletons (67%), 132 twins (21%), 48 triplets (8%), 19 quadruplets (3%) and 7 quintuplets (1%). At the first ultrasound observation of the clinical pregnancies (20-30 days, post-conception) we detected 414 single gestational scans (44%), 264 double (28%), 144 triple (10%) 76 quadruple (8%) and 35 quintuple sacs (4%). Results: A) complete pregnancy loss was observed in 22% of all pregnancies (n:160) with the following distribution: Singleton (29%), twin (10%), triplet (8%), quadruplet pregnancies (10%), and quintuplets (14%) respectively. The pregnancy loss decreased proportional to the magnitude of the multiple gestation, being statistically significantly higher in the group of patients with singletons (p<0.05). B) SPIER was found to be overall of 29% (n:293), with the following distribution; 29% in singletons, 25% in twins 24% in triplets, 45% in quadruplet pregnancies, and 54% in quintuplets, respectively. The chance of losing a gestational sac does not differ between patients that originally had a singleton, twins or triplet pregnancies. However, it was statistically greater in those that began the gestation as a quadruplet. (p<0.005). Conclusions: These results show that the frequency of complete pregnancy loss and the partial-resolution of gestational sacs (SPIER) do not have a parallel correlation in singleton and multiple pregnancies (up to quadruplets). While the complete pregnancy wastage is increased in singleton vs. multiples, the SPIER is augmented only in high order multiple gestations. This information should be used for 1) counseling of patients about the prognosis and outcome of their pregnancies from ART once clinically confirmed, and 2) to assist in making decisions about the multifetal pregnancy reductions.