Gestational diabetes mellitus (GDM) is high blood sugar that develops during pregnancy and usually resolves after the baby is delivered. Worldwide, GDM affects around 10% of pregnancies. In contrast to women who had pre-existing diabetes before pregnancies, women with true GDM do not have an increased risk of infants with birth defects. This is because the onset of GDM starts later in the 2nd or 3rd trimester which is way after the normal formation of the fetus in the womb. However, a number of complications may arise if GDM is left untreated, such as macrosomia (big baby), polyhydramnios (excess amniotic fluid), stillbirth and preeclampsia. Big baby might result in difficult delivery and injury or shoulder dystocia to the baby. Moreover, mothers may develop long-term complications of persistent diabetes after delivery. Thus treatment for GDM should not be taken lightly by pregnant mothers in order to ensure a safe and pleasant pregnancy.
Besides nutritional therapy, exercise, glucose monitoring and insulin injection, doctors may consider prescribing metformin to control GDM. Metformin is marketed under the brand name Glucophage amongst others. Naturally, concerned mothers would wonder if it is safe and effective to take glucophage throughout pregnancy. While insulin is the more preferred choice of medication for GDM, the American College of Obstetricians and Gynecologists (ACOG) have endorsed the use of metformin as one of the oral antidiabetic agents, particularly in those who declined insulin or unable to afford insulin. Metformin is also deemed as a safe and reasonable alternative to insulin by the Society for Maternal-Fetal Medicine. Other guidelines like the International Federation of Gynecology and Obstetrics (FIGO) consider metformin as an acceptable first-line oral medication for GDM in selected women.
A 2015 review reported that treatment with metformin appears to be safe and effective in the short term, but a third of them may need supplemented insulin to achieve the best blood sugar control. There is also evidence that metformin has some advantages over insulin. A 2017 meta-analysis revealed that metformin was more effective than insulin in lowering the risk of neonatal hypoglycemia, large for gestational age infants, pregnancy induced hypertension and reduced gestational weight gain. Additionally, a meta-analysis done in 2019 found that compared to insulin, metformin was able to lower birth weight and decrease the risk of macrosomia and large-for-gestational age babies.
Side effects of metformin is one of the major disadvantages of metformin. This includes metallic taste in mouth, nausea, mild anorexia, abdominal discomfort, diarrhea and gas. Hence patients are often advised to take metformin tablets with or after meals to minimise the side effects. Side effects can also be mitigated by initiating metformin at lower doses. So far, only 2% of patients had discontinued metformin due to its side effects. Besides that, evidence showed that metformin does not prevent GDM. Multiple studies showed no significant reduction in the rate of GDM when comparing metformin with a placebo.
Although metformin is able to cross the placenta and enter the fetus, it is not known yet if this is beneficial or harmful to the fetus. Certain studies showed no difference in neurodevelopmental outcomes but one study found that children who were exposed to metformin during pregnancy had higher body mass index (BMI) than those exposed to insulin. These children were larger on certain physical parameters at 4 to 9 years old. More research is needed to establish the long-term safety of metformin. Nonetheless, this does not discredit the huge amounts of benefits that metformin has to offer. Hence, pregnant mothers can rest assured that metformin, or glucophage can be taken during pregnancy for GDM. Always consult with your doctors if it is in your interest to take metformin for your GDM.