囊胚5顆之內  鮮胚植入與囊胚數量成正比
囊胚超過5顆  該周期鮮胚植入反而會下降懷孕率
囊胚超過5顆  囊胚數量與懷孕率成反比
原因再於卵巢過度刺激造成子宮內膜之干擾

Fertil Steril. 2019 Aug 5. pii: S0015-0282(19)30563-1. doi: 10.1016/j.fertnstert.2019.06.030. [Epub ahead of print]

Clinical pregnancy and live birth increase significantly with every additional blastocyst up to five and decline after that: an analysis of 16,666 first fresh single-blastocyst transfers from the Society for Assisted Reproductive Technology registry.

Smeltzer S1, Acharya K1, Truong T2, Pieper C2, Muasher S3.

OBJECTIVE:

To study the association between the number of blastocysts available and pregnancy outcomes in first fresh autologous single blastocyst transfer cycles.

DESIGN:

Retrospective cohort study.

SETTING:

Not applicable.

PATIENT(S):

Patients from the Society for Assisted Reproductive Technology reporting fertility clinics (n=16,666).

INTERVENTIONS(S):

None.

MAIN OUTCOME MEASURE(S):

Primary outcomes were clinical pregnancy (CP), live birth (LB), and miscarriage rates. Logistic regression was used to investigate the association between the number of blastocysts and each outcome.

RESULT(S):

When comparing fresh single blastocyst transfer rates, the odds of a positive pregnancy outcome (CP) increased significantly with each additional supernumerary blastocyst up to five and declined by 2% for every additional blastocyst after five. Similarly, the odds of an LB was 17% higher for each additional blastocyst up to five and declined by 2% for every additional blastocyst after five. There was no significant association between blastocyst number and miscarriage rate.

CONCLUSION(S):

Odds of positive pregnancy outcomes (CP, LB) increased significantly with every additional blastocyst up to five, but declined after that, in first fresh autologous cycles with single-blastocyst transfer. The decline after five may be explained by a detrimental effect on endometrial receptivity in patients with a large number of oocytes or inadequate selection of the best embryo for transfer based on morphology alone.