Background: Metformin is sometimes used as an alternative to insulin in gestational
diabetes mellitus (GDM). It is also used to achieve ovulation in polycystic ovary syndrome (PCOS).
Pre-natal exposure to metformin results from its continuation after a successful ovulation in women
with PCOS, its maintenance in women with pre-gestational diabetes or the installation of metformin
in GDM. Little is known about the potential consequences of metformin exposure on pregnancy
outcomes and offspring development. The aim of this review is to summarize the metformin effects
on pregnancy outcomes and offspring development. Gaps in the available evidence and unanswered
questions are also discussed.
Methods: A comprehensive literature search was carried out to identify eligible studies from
MEDLINE/PubMed, EMBASE and SCIELO databases through 1995 first semester.
Results: Several factors limit the effect of metformin on embryos. In contrast, placental transport of
metformin is effective allowing for a higher fetal exposure; the impact of this finding remains
unclear. It seems that the interruption of metformin after a pregnancy diagnosis in women with
PCOS is not associated with a higher miscarriage risk and it continuation does not seem to impair
the maternal metabolic prognosis or prevent emerging GDM.
Conclusions: It seems to have no sense to prolong the use of metformin after a pregnancy diagnosis
in women with PCOS. Patients with GDM may be treated with metformin under on judicious basis,
and a careful attachment to clinical guidelines and regulations is recommended. The long-term
effects of pre-natal exposure to metformin on the offspring remain uncertain
Keywords: Metformin, gestational diabetes mellitus, polycystic ovary syndrome, pregnancy outcomes
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