懷孕從受精開始到胎兒出生結束，是一個漫長的發(fā)育過程。妊娠失敗，或稱為妊娠丟失或流產，可以發(fā)生在妊娠的不同階段，并且可能涉及許多不同的病理生理學機制。孕期是一個發(fā)展的過程，很難去定義每個不同階段的妊娠情況。不過，早期妊娠通常是指著床后至第三個月的妊娠階段，這可以進一步分為:(I):臨床前妊娠，只能通過HCG水平漲值來辨別，以及(II)超聲或組織學證據可以證明的臨床妊娠。

　　In the past, focus was given primarily to those pregcy failures occurring after a clinically recognized gestation, as preclinical pregcy losses would commonly go unnoticed or present merely as a late period. However, with the development of over-the-counter pregcy testing kits for early pregcy recognition, and the widespread use of ART, the focus of interest in pregcy failure has gradually shifted to the earlier stages of gestation. As a result, it has become increasingly evident that even women with normal fertility appear to have a large number of pregcy losses occurring at a very early gestational stage.

　　在過去，臨床妊娠后的流產現象備受關注，原因是臨床前妊娠失敗容易容易受到忽視或僅在較晚的時期出現。然而，隨著用于早期妊娠鑒別的非處方妊娠檢測試劑盒的發(fā)展，以及輔助生殖技術的廣泛使用，對妊娠失敗的關注焦點已逐漸轉移到妊娠的早期階段。結果顯示，即使是生育能力正常的婦女，也會在妊娠早期頻發(fā)流產。

　　Roberts and Lowe were among the first to demonstrate the scale of early pregcy wastage, by using the registered number of births in England and estimating the number of fertile ovulatory cycles in married couples having unprotected intercourse. They calculated that only 22% of cycles exposed to the risk of pregcy actually resulted in a live birth (1). Because the sporadic miscarriage rate of pregcies is far less than 78%, this finding implied that the vast majority of pregcies were being lost at a very early stage, before they were clinically recognized. In fact, a review of the literature suggests that of all pregcies, approximately 30% fail prior to implantation, a further 30% fail following implantation but prior to clinical evidence of pregcy, and about 10% suffer clinical miscarriages. This means that only 30% of all conceptions in fertile women will result in a live birth (2).

　　Roberts和Lowe是兩位最早通過使用英國登記的出生人數，并估算已婚夫婦無保護措施性行為的可育排卵周期數，來說明早期妊娠流產規(guī)模的研究人員。結果表明只有22%的周期最終妊娠并且有嬰兒出生(數據參考見1)。由于妊娠的偶發(fā)性流產率遠低于78%，這一發(fā)現意味著，絕大多數的妊娠是在臨床確認之前就流產了。事實上，文獻回顧表明，在所有妊娠中，大約30%的胚胎沒有著床，另有30%在著床后和臨床妊娠確認前丟失，約10%遭遇臨床流產。這意味著，在育齡女性中，女性的所有受孕中只有30%的概率會誕生一名嬰兒(數據參考見2)。

　　References 數據參考：

　　1. Roberts CJ, Lowe CR. Where have all conceptions gone ? Lancet 1975; 1:498-499

　　2. Macklen NS, Geraedts JP, Fauser BC. Conception to ongoing pregcy : the “black box” of early pregcy loss. Hum Reprod Update 2002; 8:333-343.

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