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Antibiotics During Pregnancy-New Study Suggests Obesity As Possible Side Effect

A new study in 2014, by the NYU Langone Medical Center, has revealed that early antibiotic use, in a study, carried out on mice could make them more susceptible to metabolic abnormalities and obesity later in life. Some mice were given low doses of penicillin for life from the last week in pregnancy, and others were given the same doses during nursing.

What is made clear by the study is the disruption of the bacterial landscape in the gut, at a stage of early development? It shows that when even low doses of antibiotics are administered, the body’s metabolism is reprogrammed. This in turn set up a predisposition to metabolic abnormalities and obesity.

1. Antibiotics during pregnancy alter the gut bacteria in mice

In fact, the study showed that it is not the antibiotics themselves which drive these metabolic effects, but however, the gut bacteria which have been altered. The researchers of the study have stressed that currently more evidence would be necessary before we can determine whether early use of antibiotics can lead to obesity also in humans. One part of the study was an experiment with three different groups of mice.

The first group were given antibiotics in low doses from the last week of pregnancy, and these doses were continued to be administered throughout their lives. The second group were given the same amount of penicillin, after weaning, and they also continued to receive these doses for the rest of their lives. The final group were not given any antibiotics.

During this experiment, it was evident that both of the groups which received penicillin saw an increased fat mass in their bodies. However, the increase in fat mass was higher in the group of mice which received penicillin during the last week of pregnancy in the womb.

2. Testing with a high-fat diet

A normal female adult mouse carries 3 grams of fat. Another aspect of the study was feeding the mice a high-fat diet. As a result of this high-fat diet the mice who had not been administered antibiotics, but were fed the high-fat diet, ended up with 5 grams of fat. However, the groups of mice that had received antibiotics, as well as the high-fat diet, ended up with 10 grams of fat.

Also, mice who received the antibiotics suffered from other effects, which we see in human obese patients – such as changes in their genes in relation to detoxification and liver regeneration, as well as elevated levels of fasting insulin.

carbon monoxide poisoning pregnancy

3. Confirmation of the landmark research by Dr Blaser’s lab published in Nature in 2012

This landmark research of 2012 revealed that when mice who were on a normal diet, were given low doses of antibiotics during their life, their body fat mass increase by between 10 to 15%, more than the mice who did not receive antibiotics. Additionally, that research also noted a significant alteration in the metabolism of their livers.

One of the unanswered questions of the 2012 study was whether the metabolic changes were caused as a result of antibiotic exposure or altered bacteria? However, this latest study answers this question. It shows that altered microbes are what drive the obesity effects.

4. Antibiotics during pregnancy – the current stance

I would like to reiterate the earlier statement – that the researchers of this recent study have made it perfectly clear that further studies will be required, to confirm as to whether this may be the case also in humans. The purpose of this section of the website, and this feature, is purely to gather and inform you of the latest research.

The current stance on taking antibiotics during pregnancy is that it is okay to do so, but only with some types of antibiotics. How your medical team will judge this, depends on a variety of safety factors, such as what stage of pregnancy you are at, what is the type of antibiotic and how long you will need to take it for.

You should never take any antibiotics during pregnancy without consulting your medical team. For example, the combination of trimethoprim and sulfamethoxazole, has been linked with causing birth defects.

These two antibiotics are often used in conjunction with each other to treat urinary tract infections. Another example of antibiotics should definitely be avoided during pregnancy are tetracyclines. These have the potential to damage your liver and also to discolour your baby’s teeth

5. Below is a sample of some of the antibiotics that are sometimes considered to be safe during pregnancy

  • Amoxicillin
  • Ampicillin
  • Clindamycin
  • Erythromycin
  • Penicillin
  • Nitrofurantoin

An earlier study that dates back to 2009, drew up the following guidelines:

  1. Antibiotics during pregnancy should only be used if absolutely indicated. Therefore any infection must be medically confirmed, and the medications chosen accordingly.
  2. If at all possible doctors should avoid starting a course of antibiotics during the first trimester. – In other words that should be ideally an antibiotic that you are patient has a proven, positive track record with.
  3. Single agent therapy is always preferable over polypharmacy.
  4. Make sure you discourage patients use of over-the-counter drugs, explaining to her that they could interfere with the metabolism and efficacy of what you have prescribed.

If you wish to reference these studies they are linked below: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2760892/ http://www.sciencedaily.com/releases/2014/08/140814123426.htm

Midwife sonographer facilitated

Consultant Led, Centre of Medical Excellence 


All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.


This website was formerly Merrion Fetal Health. The clinic has undergone a rebrand and is now known as Merrion Ultrasound.