Embryo freezing for preventing ovarian hyperstimulation syndrome

More research is needed to determine whether using frozen embryos and or intravenous albumin can reduce the rate of severe ovarian hyperstimulation syndrome in IVF. Ovarian hyperstimulation syndrome (OHSS) is a complication of using hormones to induce ovulation (stimulate the release of eggs) in IVF (in vitro fertilisation). The drugs can sometimes over-stimulate ovaries. Severe OHSS can be life-threatening. Fewer hormones are needed if frozen embryos are transferred in a subsequent cycle, although this lowers pregnancy rates. However, this update the review first published in 2002 (D'Angelo 2002) found there is not enough evidence to show whether using frozen embryos and or intravenous albumin infusion (artificial fluid to increase the woman's blood volume) can reduce OHSS in women who are at high risk. More research is needed on effects on pregnancy rates.

Authors' conclusions: 

This updated of the review (D'Angelo 2002) has showed that there is insufficient evidence to support routine cryopreservation and insufficient evidence for the relative merits of intra-venous albumin versus cryopreservation.

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Background: 

Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic potentially life threatening condition resulting from an excessive ovarian stimulation. Its reported incidence varies from one percent to ten percent of in vitro fertilization (IVF) cycles. It seems likely that the release of vasoactive substances, secreted by the ovaries under human chorionic gonadotropin (hCG) stimulation plays a key role in triggering this syndrome. The hallmark of this condition, is a massive shift of fluid from the intra-vascular compartment to the third space resulting in profound intra-vascular depletion and haemoconcentration.

Objectives: 

To evaluate
(i) the effectiveness of cryopreservation (embryo freezing) for the prevention of OHSS when compared with human intra-venous albumin infusion
(ii) the effectiveness of the elective cryopreservation (embryo freezing ) of all embryos for the prevention of OHSS when compared with fresh embryo transfer.

Search strategy: 

We searched the Cochrane Menstrual Disorders and Subfertility Review Group specialised register of controlled trials up to April 2007. In addition, MEDLINE (PUBMED 1985 to March 2007), EMBASE (1985 to April 2007), CINAHL (1985 to March 2007) and the National Research Register (April 2007) were searched.

Selection criteria: 

Randomised controlled trials (RCTs) in which either human intra-venous albumin or cryopreservation of all embryos were used as a therapeutic approach to OHSS were included.

Data collection and analysis: 

The interventions compared were cryopreservation (embryo freezing) versus intra-venous human albumin administration and elective cryopreservation of all embryos versus fresh embryo transfer. The primary outcomes were: incidence of moderate and severe OHSS versus nil and or mild OHSS, clinical pregnancies and or woman. The secondary outcomes were: number of oocytes retrieved, number of oocytes fertilized, number of embryos transferred, number of embryos frozen, multiple pregnancy rate, live birth rate, number of women admitted to the hospital as inpatient or outpatient and time to the next menstrual period (resolution time). Statistical analysis was performed in accordance with the Cochrane Menstrual Disorders and Subfertility Group guidelines.

Main results: 

No new studies found for inclusion in the update of this review, the results from the original review published Issue 2 , 2002 (which identified seventeen studies) remain unchanged. It therefore remains that two studies of which met our inclusion criteria one study was included where cryopreservation (embryo freezing) was compared with intra-venous human albumin administration (Shaker 1996) and one study was included where elective cryopreservation of all embryos was compared with fresh embryo transfer (Ferraretti 1999). When cryopreservation was compared with intra-venous human albumin administration no difference was found in all the outcomes examined between the two groups. When elective cryopreservation of all embryos was compared with fresh embryo transfer no difference was found in all the outcomes examined between the two groups.

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