The association between the type of progesterone supplementation and miscarriage risk in women who have had a positive pregnancy test following embryo transfer: a retrospective cohort study

Abstract

Purpose: The purpose of this study was to identify if switching from intramuscular (IM) to vaginal progesterone compared to staying on IM progesterone after a positive pregnancy test following embryo transfer (ET) is associated with miscarriage risk.

Methods: A retrospective cohort study was performed in a private university-affiliated fertility clinic and included women aged 18-50 years with a positive pregnancy test following ET. The two groups studied were: women who stayed on IM progesterone following a positive pregnancy test and those who switched to vaginal progesterone after a positive test. The main outcome measured was risk of miscarriage < 24 weeks gestation as a proportion of non-biochemical pregnancies.

Results: 1988 women were included in the analysis. Among the baseline characteristics, the presence of prior miscarriages as well as prior failed ETs, and frozen cycles (vs fresh) as type of transfer were associated with IM progesterone use (p values ≤ 0.01). As per miscarriage risk < 24 weeks, 22.4% (274/1221) of patients in the IM progesterone group experienced a miscarriage compared with 20.7% (159/767) in the vaginal progesterone group (OR 0.90; 95% CI 0.73-1.13). A multivariable logistic regression model revealed an adjusted OR (aOR) of 0.97 (95% CI 0.77-1.22).

Conclusion: This study suggests that switching from IM to vaginal progesterone after a positive pregnancy test following an ET is not associated with miscarriage risk. Considering that IM progesterone imposes substantial discomfort, this study offers reassurance and some flexibility in treatment protocols. Further prospective studies are necessary to corroborate the results of this study.

Keywords: In vitro fertilization; Intramuscular progesterone; Luteal phase support; Miscarriage; Vaginal progesterone.