Metformin for gestational diabetes – what it is and how it works

In the UK it is common to use Metformin for gestational diabetes where dietary and lifestyle changes are not enough to lower and stabilise blood sugar levels. It is widely used to help lower fasting blood sugar levels as well as post meal levels.

Metformin is an oral medication in tablet form.  It is used in diabetics to help the body use insulin better by increasing how well the insulin works. In pregnancy it can be used in women who have diabetes before becoming pregnant (Type 2 diabetes) and in women who develop diabetes during pregnancy (gestational diabetes). Metformin is also used for other conditions too, commonly used in those that have PCOS (polycystic ovarian syndrome).

Metformin is a slow release medication.


Metformin for gestational diabetes


facebookHere are the most commonly asked Q&A on Metformin for gestational diabetes from our Facebook support group

Why do I need to take Metformin?

For many ladies with gestational or type 2 diabetes, if lower blood sugar levels cannot be reached through diet and exercise then medication will be required to assist.  If blood sugar levels remain high, then the diabetes is not controlled and can cause major complications with the pregnancy and baby.

Some consultants will prescribe Metformin on diagnosis of gestational diabetes on the basis of your GTT results. Others will let you try diet control first and when blood glucose levels rise out of target range, or close to the target range, they may prescribe Metformin as a way to help lower and control your levels.

NICE guidelines regarding the timing and use of Metformin for gestational diabetes

1.2.19 Offer a trial of changes in diet and exercise to women with gestational diabetes who have a fasting plasma glucose level below 7 mmol/litre at diagnosis. [new 2015]

1.2.20 Offer metformin[4] to women with gestational diabetes if blood glucose targets are not met using changes in diet and exercise within 1–2 weeks. [new 2015]

1.2.21 Offer insulin instead of metformin to women with gestational diabetes if metformin is contraindicated or unacceptable to the woman. [new 2015]

1.2.22 Offer addition of insulin to the treatments of changes in diet, exercise and metformin[4] for women with gestational diabetes if blood glucose targets are not met. [new 2015]

1.2.23 Offer immediate treatment with insulin, with or without metformin[4], as well as changes in diet and exercise, to women with gestational diabetes who have a fasting plasma glucose level of 7.0 mmol/litre or above at diagnosis. [new 2015]

1.2.24 Consider immediate treatment with insulin, with or without metformin[4], as well as changes in diet and exercise, for women with gestational diabetes who have a fasting plasma glucose level of between 6.0 and 6.9 mmol/litre if there are complications such as macrosomia or hydramnios. [new 2015].

1.2.25 Consider glibenclamide[5] for women with gestational diabetes:

  • in whom blood glucose targets are not achieved with metformin but who decline insulin therapy or
  • who cannot tolerate metformin. [new 2015]

SIGN (Scottish) guidelines:

Glucose-lowering therapy should be considered in addition to diet where fasting or two hour glucose levels are above target, for example, where two or more values per fortnight are: ƒ

  • ≥5.5 mmol/l preprandial or ≥7 mmol/l two hours postprandial on monitoring at ≤35 weeks ƒ
  • ≥5.5 mmol/l preprandial or ≥8 mmol/l two hours postprandial on monitoring at >35 weeks,
  • or any postprandial values are >9 mmol/l
When should I take Metformin?

Your diabetes health care professional will advise when you should take your Metformin. You may need to take Metformin at one or all of your meals, but it is commonly prescribed to be taken in the morning with breakfast and/or with your evening meal.


Does Metformin cause any side effects?

prolonged release metforminNot all people suffer side effects with Metformin. However, Metformin can very often cause gastric side effects such as nausea, loose stools (diarrhoea) cramps or stomach upset. Sometimes people can get these side effects when starting the medication, but after a few days they should stop.  It is also common to experience side effects when a dose is increased.

If side effects continue longer than a week, contact your diabetes team who may advise you to stop the Metformin or reduce the dose. There is also a slower prolonged release metformin which can be prescribed which may improve side effects.

If you are not able to tolerate the side effects at all, usually insulin injections will be given as an alternative.

Other common side effects of Metformin are flatulance (particularly smelly trumps, known in our Facebook support group as MetFARTmin!) and lack/loss of appetite as Metformin is an appetite suppressant.


Is there anything I can do to avoid or lessen the side effects of Metformin?

Taking Metformin with or after food helps to ease any side effects.  The best result for many has been taking the Metformin halfway through the meal. When starting Metformin you could also start on a low dose, slowly increasing it over a few days – Please ask your diabetes health care professional if this is acceptable for you to do.


The tablets are HUGE?!

metformin large pillsThere are many different brands of Metformin and some are very large in size which causes some ladies issues with swallowing such large pills. Smaller tablets are available and so you could ask your Pharmacist to provide smaller tablets, or try different dispensaries.

Metformin is available in liquid form but it is rarely prescribed. If you feel swallowing the pills will be an issue then you should discuss this with your diabetes health care professionals.


How soon does it take for Metformin to take effect?

Metformin takes a little while to build up in your system.  Some less insulin resistant ladies may see an improvement in blood sugar levels very soon, but for others it may take well over a week – 2 weeks, OR increased doses before any difference is seen.


Now that I am taking Metformin for gestational diabetes can I go back to eating a ‘normal’ diet?

Please do not be under the impression that it is a ‘magic pill’ or miracle cure for gestational diabetes.  It is very important to still follow a good GD diet and to exercise.  Metformin will help you use your  body’s insulin better, but you are still insulin resistant and so poor food or drink choices will still raise your blood sugar levels too high.  You may however be able to eat more substantial meals than you had previously been able to tolerate and may feel much better, gaining more energy as a result.


What if the Metformin doesn’t work?

If your blood glucose levels do not improve with Metformin, diet and exercise, insulin will usually be used to help achieve the blood glucose levels required whilst you are pregnant.  Please do not be disheartened if this happens. The further into pregnancy you go, the more insulin resistant you become and so very often insulin may also be introduced to help control levels. To read about insulin and how it used for gestational diabetes, please take a look at this page.


Can Metformin and insulin be taken together?

Yes, very often Metformin is the first step of treatment to help lower blood glucose levels, but if further help is needed then insulin is often used alongside Metformin.  Insulin and Metformin are commonly used alongside each other as it means that less insulin is needed to achieve the desired results.  This is preferential as insulin resistance worsens the more insulin taken therefore it is better to have a mix of the two than just insulin alone.


Will I need to take Metformin after my baby is born?

As you get near to the end of pregnancy and your labour plans are discussed, you will be advised what you need to do with regards to your Metformin and when to stop it.  If you were not taking Metformin previous to being pregnant then you will stop taking it once your baby is born.

Metformin is commonly given to those diagnosed with type 2 diabetes and so if you are diagnosed following the birth of your baby, at your post birth diabetes screening test then you may be re-prescribed this medication although doses may be different to what was required during your pregnancy. For more information on post birth diabetes testing, more information is available here.


Will taking Metformin for gestational diabetes change anything during my labour?

induction of labourDepending on your blood glucose levels, baby’s growth, hospital and NHS Trust guidelines and any other complications, you may be advised to have an induction (or planned caesarean section if you need this for other reasons) from anywhere around 37 weeks – 40+6 weeks.

Due to gestational diabetes, during the actual labour, you may also be given insulin via an intravenous drip if your blood sugar levels are unstable (even if you were not using insulin therapy through your pregnancy).  This is where an insulin and glucose drip is used, known as a ‘sliding scale‘.   It is best to discuss this with your consultant to see what is likely to be offered and advised for YOUR situation. Please note: Not all ladies are given a sliding scale during labour.  NICE guidelines recommend “Advise women with uncomplicated gestational diabetes to give birth no later than 40+6 weeks.”

For further information on birth and induction of labour with gestational diabetes, take a look at our page on induction and home or water births.


NICE guidelines regarding timing and mode of birth in gestational diabetes

1.4.4 Advise women with gestational diabetes to give birth no later than 40+6 weeks, and offer elective birth (by induction of labour, or by caesarean section if indicated) to women who have not given birth by this time.[new 2015]

1.4.5 Consider elective birth before 40+6 weeks for women with gestational diabetes if there are maternal or fetal complications. [new 2015]

1.4.6 Diabetes should not in itself be considered a contraindication to attempting vaginal birth after a previous caesarean section. [2008]

1.4.7 Explain to pregnant women with diabetes who have an ultrasound‑diagnosed macrosomic fetus about the risks and benefits of vaginal birth, induction of labour and caesarean section. [2008]

Does Metformin cross the placenta?

Yes, Metformin crosses the placenta in significant amounts.


Is Metformin licensed for use in pregnant women in the UK?

No, however, there have been clinical trial proving it’s use is safe. Please read below…


Is Metformin safe for me & my baby to take during pregnancy?

Yes, the MiG (Metformin in Gestational diabetes) trial from May 2008, observed the use of Metformin in pregnancy and has shown that it is safe to use during pregnancy. National Diabetes Guidelines, NICE and the British National Formulary say Metformin can be used in Pregnancy. **You need to be aware that the patient leaflet which comes with the medication will say otherwise.


Can taking Metformin cause a hypo (blood sugar levels <4.0mmol/L)?

This is a debatable subject as there seems to be differing opinions on this from different medical professionals. Metformin can cause blood sugar levels to drop lower which may cause hypo type symptoms such as the following:

  • Sweating
  • Anxiety or bad temper
  • Trembling/shaking
  • Tingling of the lips or fingers
  • Intense hunger
  • Going pale
  • Dizziness
  • Palpitations (heart beating rapidly)
  • Confusion
  • Lack of concentration
  • Lack of co-ordination

HOWEVER, Metformin cannot cause blood sugar levels to drop so low that it would cause a life threatening situation where your brain cannot function.  Therefore this is known as a ‘false hypo’. If your levels drop low, your liver will dump glucose into your bloodstream which will raise your levels.  This does not happen to those who are treated with insulin or Glibenclamide and this is why insulin or Glibenclamide dependant diabetics have to ‘treat’ the hypo with something high in glucose to raise their levels and counteract the insulin. For more information on false hypos please read more here.


What to do if you use Metformin for gestational diabetes and you experience hypo type symptoms

If your blood sugar levels drop low whilst taking Metformin and you experience hypo type symptoms, the best thing to do is eat a normal, GD friendly meal or snack and this should raise your levels sufficiently to make you feel better. If you ‘treat’ the hypo as an insulin dependant diabetic would, with something high in glucose, then you run the risk of raising your blood sugar levels too high, which in turn can make you feel unwell and is not good for your baby. These hypo type symptoms are known as ‘false hypos’. Metformin cannot cause hypoglycaemia. For more information on false hypos, please read more here.



Are there any side effects to my baby once born from taking Metformin?

There are no known side effects to the baby from taking Metformin in pregnancy.

There is currently research taking place as to what the longer term effects to the children born to mothers taking Metformin during pregnancy are.  This drug was only introduced for use during pregnancy for those diagnosed with gestational diabetes following the MiG trial in 2008, therefore they are still researching what effects Metformin has on the offspring as they reach adulthood.  It is thought that there are many benefits such as decreased risk of developing type 2 diabetes and decreased risk of obesity – but this is yet to be proven.  So far the most recent research available is the MiG TOFU, taken at the age of 2 years following birth. For links to these research trials, please scroll to the bottom of this page.


Is it safe to drive whilst taking Metformin?

Yes – you do not need to notify the DVLA that you are being treated with Metformin. You must by law, inform your insurance company if you have diabetes, no matter how it is treated.  If you fail to do so, your insurance may be invalid. Take a look at our information on gestational diabetes and driving here.

I’ve started taking Metformin for gestational diabetes yet my levels have not come down or seem worse?

For many, low doses of Metformin are given to start with and whilst this may make immediate difference for some, for many others it takes a while for the Metformin to build up in your system or to get the dose correct.  Keep in touch with your diabetes team to discuss blood sugar levels and doses.  Metformin cannot cause higher blood sugar levels, but gestational diabetes is a progressively worsening condition. As gestational diabetes is driven by hormones, things can change overnight and often this may coincide with starting medication and often confuse things. Call your diabetes health care professionals with any concerns.


HG (severe sickness in pregnancy) and Metformin

Some GD HG Mums have reported that using Metformin for gestational diabetes has actually helped their HG symptoms, others have concerns over taking a medication which they feel may worsen their HG. Discuss any concerns you have with your diabetic consultant and/or midwife who may be able to help you. If you need additional help with lowering blood sugar levels and do not feel Metformin is suitable for you, then please be aware that in the majority of cases, insulin will be offered as an alternative. Occasionally Glibenclamide may be offered as an alternative medication to Metformin too. For further information on HG and GD, please take a look at this page.



The MiG (Metformin in Gestational diabetes) trial  published May 2008

Metformin in Gestational Diabetes: The Offspring Follow-Up (MiG TOFU) Body composition at 2 years of age  published 2011

Metformin Therapy During Pregnancy – Good for the goose and good for the gosling too? published 2011

A higher level of evidence has come from randomized clinical trials using metformin in the treatment of women with GDM. In the Metformin in Gestational Diabetes (MiG) trial, the largest study so far reported of metformin use in women with GDM, 751 women were randomized to receive either metformin or insulin (12). There was no significant difference in the composite fetal outcome between the two groups although preterm birth was found to be increased in the metformin group. Women in the metformin group had less weight gain compared with women in the insulin group. The results provide further evidence regarding the safety of metformin in pregnancy. A comparable, but much smaller, randomized trial of 63 patients found similar results (13).

Clinical experience and the evidence published thus far support the safety and efficacy of metformin use in pregnancy with respect to the immediate pregnancy outcomes. However, does the use of metformin in pregnancy ultimately have a beneficial, neutral, or deleterious effect on the offspring? While the results of Rowan et al. (21) on this issue are both encouraging and reassuring, and the possibility of benefit in children and adolescents with in utero exposure to metformin is intriguing, the long-term impact—positive or negative—of metformin use is still largely an unknown quantity. This work is the first of several necessary steps toward answering this important question.

Efficacy and safety of metformin during pregnancy in women with gestational diabetes mellitus or polycystic ovary syndrome: a systematic review. published July 2013

Metformin appears to be effective and safe for the treatment of gestational diabetes mellitus (GDM), particularly for overweight or obese women. However, patients with multiple risk factors for insulin resistance may not meet their treatment goals with metformin alone and may require supplementary insulin. Evidence suggests that there are potential advantages for the use of metformin over insulin in GDM with respect to maternal weight gain and neonatal outcomes. Furthermore, patients are more accepting of metformin than insulin. The use of metformin throughout pregnancy in women with polycystic ovary syndrome reduces the rates of early pregnancy loss and preterm labor and protects against fetal growth restriction. There have been no demonstrable teratogenic effects, intra-uterine deaths or developmental delays with the use of metformin.