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Is It Safe To Use Metformin During Conception and Pregnancy?

The following recent query requested my opinion regarding the safety of metformin during the periconceptual period and throughout pregnancy. Although there are not many large or comprehensive studies addressing these concerns, the bulk of the data available to us is encouraging…

Dr. T,

Quick opinion if you don’t mind. As you may recall, I miscarried on 9/12. I have since seen my PCP for a regular check-up. He prescribed me Metformin….he believes based on my history, weight, blood work and family history, my body may have issues with the breakdown of sugars (i.e., type 2 diabetes but I’m not diagnosed with that). He said that it also may have some positive side effects for me including weight loss and assistance in helping me to conceive (although that doesn’t appear to be a problem since I WAS able to get pregnant even though I miscarried). He says it is completely safe.

I have read mixed things online about Metformin and potential effects on babies. Namely that no known birth defects have been caused from it but that there are not many studies either. Additionally, I have read some things about it potentially causing miscarriage.

Could you please give me your opinion on this? I would like to take it as I have for a week now, because I physically feel better. I’m very scared of the effect it may have of a pregnancy and if I were to stop taking it during my pregnancy (as my doctor said this is elective as he feels it would benefit me but is not imperative for me to take). Do you know of any potential miscarriage issues with this prescription?

Thanks again for EVERYTHING!


Women with insulin resistance are at increased risk for hyperinsulinemia, type 2 diabetes, polycystic ovary syndrome (PCOS), and hyperandrogenism (increased levels of ‘male hormones’). They also are at risk for reduced fertility secondary to ovulatory dysfunction and a suboptimal hormonal milieu that may impair conception, implantation, and placentation. Pregnancy complications include higher rates of miscarriage, gestational diabetes, hypertensive disorders, preterm delivery and operative deliveries, excessive maternal weight gain, fetal macrosomia as well as growth restriction, and admission of their babies to neonatal intensive care units for a variety of reasons (Boomsa, et al., Semin Reprod Med. 2008;26:72-84). In my own experience, they also appear to be at increased risk for complications related to cervical insufficiency.

Metformin is an oral hypoglycemic (blood sugar lowering) agent whose primary affect seems to be mediated through its ability to reduce insulin resistance, thereby leading to a reduction in blood glucose and insulin levels. Metformin has also been found to have other beneficial affects, some of which appear to be independent of its hypoglycemic activity. Included among these are its effects on lipids, inflammation, hemostasis, and endothelial cell and platelet function (Anfossi G, et al. Curr Vasc Pharmacol. 2010 Jan 1. [Epub ahead of print]; Matsumoto T, et al., Am J Physiol Heart Circ Physiol. 2008;295:H1165-H1176).

In women with PCOS, “reduction of hyperinsulinemia with metformin and diet is associated not only with improvement of the biochemical endocrinopathy, but, commonly, with restoration of menstrual cycles and fertility (Goldenberg, et al, Minerva Ginecol. 2008;60:63-75).” When used in infertile women with PCOS in combination with clomiphene citrate, an ovulation-inducing drug, metformin was shown to improve conception rates and, perhaps, live-birth rates compared to either drug alone (Legro, et al., N Engl J Med. 2007;356:551-66). In a recent small study of 66 women with PCOS who were clomiphene resistant and underwent in vitro fertilization, those who “received metformin (until conception) showed a significantly higher number of good quality embryos and implantation rate when compared with the placebo controls (Qublan, et al., J Obstet Gynaecol. 2009;29:651-5).” They were also found to undergo fewer spontaneous abortions in early pregnancy.

Very few studies have been done in which metformin therapy has been continued throughout the pregnancy, but in those that have, the results have been encouraging. Khattab and colleagues (Gynecol Endocrinol. 2006;22:680-4) studied 200 nondiabetic women who took metformin while undergoing assisted reproduction, of which 80 stopped the drug once they conceived and 120 continued it throughout pregnancy. Demographically, both groups were similar. Miscarriage rates “in the metformin group were 11.6% compared with 36.3% in the control group (p < 0.0001; odds ratio = 0.23, 95% confidence interval 0.11-0.42).” Similarly, Nawaz and colleagues (J Obstet Gynaecol Res. 2008;34:832-7), found that “In women with PCOS, continuous use of metformin during pregnancy significantly reduced the rate of miscarriage, gestational diabetes requiring insulin treatment and fetal growth restriction.” Furthermore, no significant congenital anomaly, intrauterine death or stillbirth in any of the woman who took metformin during in this study.

To support the observations in humans and, perhaps, to provide a mechanism of action, Luchetti and colleagues (J Steroid Biochem Mol Biol. 2008;111:200-7) found in mouse studies that hyperandrogenization, such as that which occurs in PCOS, induces embryo resorption in early pregnancy and that this is correlated with reduced production of progesterone-induced blocking factor and increased production of cyclooxygenase-2 (COX-2) – the overall effect of these changes creating a pro-inflammatory environment. Coincident treatment with metformin is able to reverse such changes and prevent early pregnancy loss in this animal model. To further support the overall beneficial effect of metformin in human pregnancy being the result of its overall anti-inflammatory properties, Orio and colleagues (Eur J Endocrinol. 2007;157:69-73) found in nonpregnant PCOS women that metformin treatment significantly reduced WBC count and C-reactive protein (CRP), reduced androgens, reduced low density lipids, and increased high-density lipids – all contributing to a reduction in the “proinflammatory” status of those PCOS women receiving metformin.

Finally, to answer our reader’s final concerns, in all the studies we have reviewed, in no instance did taking metformin, either during conception or throughout any time frame of pregnancy, appear to have a serious deleterious affect on the babies. Although the studies have been small, there does not appear to be a greater risk for spontaneous abortion, later pregnancy loss, or congenital anomalies (Goldenberg, et al., Minerva Ginecol. 2008;60:63-75; Nawaz, et al., J Obstet Gynaecol Res. 2008;34:832-7; Qublan, et al., J Obstet Gynaecol. 2009;29:651-5; Elizur, et al., Fertil Steril. 2008;89:1595-602; Bolton, et al., Eur J Pediatr. 2009;168:203-6; Ekpebegh, et al., Diabet Med. 2007;24:253-8). Furthermore, Bolton and colleagues (Eur J Pediatr. 2009;168:203-6) have reported that metformin is actually associated with beneficial effects of fewer growth restricted (< 10th percentile) and macrosomic (> 90th percentile babies) and fewer cases of neonatal hypoglycemia requiring glucose infusion.

This post, Is It Safe To Use Metformin During Conception and Pregnancy?, was originally published on by Kenneth Trofatter, M.D., Ph.D..

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