Research indicates that sleeping on side can help babies' growth

New research has found links between low birth weight and sleeping on your back during the third trimester.

Pregnant woman sleeping on her side

New research has found links between low birth weight and sleeping on your back during the third trimester. This finding has come from scientists at the University of Auckland.

More than 1,700 women, all of whom were at least 28 weeks pregnant, were asked about how they position themselves when they sleep.  The results of the study were based on how the women had fallen asleep in the past 1 to 4 weeks.  The position you fall asleep in is often the position you stay in for the majority of the night.

The results showed the following:

  • Average weight of baby when mothers slept on their backs: 7lbs 8oz (3.41kg)
  • Average weight of baby when mothers slept in another position e.g. side: 7lbs 13oz (3.55kg) 
  • This is a difference of 5oz (144g) in weight, although both weights are considered ‘normal’*

*According to the University of Michigan, the average birth weight for newborn babies is around 7.5lb (3.5kg).  However, babies born between 5.5lb (2.5kg) and 10lb (4.5kg) are considered normal weight. 

Current research suggests that lying on your back in late pregnancy can compress blood flow around your body, lowering supplies of oxygen and nutrients to the developing fetus. This study indicates that this restricted blood flow could have an impact on the growth of the fetus in the womb.

When babies weigh too little, it can lead to health problems or complications before or after they are born. Lead author Dr Ngaire Anderson has suggested that “this reduction in birthweight with back sleeping could partly explain the relationship we have seen between back sleeping and elevated risk of stillbirth”.  However, the researchers are urging mothers not to panic if they wake up on their backs:

“[If you wake up on your back] just settle back to sleep on your most comfortable side. Also, our advice is the same whether you’re going to bed at night or lying down for a daytime nap.” Professor Lesley McCowan, Senior author and Head of University's Department of Obstetrics and Gynaecology.

Dr Ngaire Anderson suggests that the findings reinforce the need for an ongoing public health campaign to raise awareness of the effects of sleeping on side.  This is not only for the associated risk of stillbirth, but also for the added benefit of helping their babies reach a healthy birth weight.

Tommy’s Sleep On Side campaign

In 2017 Tommy’s launched the Sleep On Side campaign, with the aim of raising awareness of the link between the mother sleeping on her back in the third trimester and stillbirth.  The findings from this new research highlight how important it is that research into safe sleeping continues, in order to keep women informed about actions that can help protect themselves and their babies.

You can watch our campaign film below:


Read more pregnancy news

  • Illustration of woman fighting back against a cloud of unwanted comments


    Dear pregnant me...let's talk about unwanted advice

    Things I wish I had known when I was pregnant about...unwanted advice. People generally mean well, but at the end of the day, you and your partner (if you have one) are the only ones who get to decide how to raise your baby.

  • woman thinking


    Coronavirus and trying to get pregnant

    We understand that the recent news regarding coronavirus is unsettling and may be causing some anxiety. You may have been planning to get pregnant this year and now have lots of questions about whether you should go ahead or wait a while. This is your decision but we have tried to answer any questions you may have below.

  • Pregnant Woman Meeting With Nurse In Clinic


    Pregnancy and coronavirus: information for pregnant women and new mums

    The Royal College of Obstetricians & Gynaecologists has released official guidelines to outline information for pregnant women and new mums surrounding the recent outbreak of coronavirus (COVID-19). Try not to worry and follow any advice in these guidelines. We are updating this page as new information is published.

  • Pill bottle spilling out pills onto surface.


    New study into effects of taking Macrolide antibiotics during pregnancy

    Macrolide antibiotics (including erythromycin, clarithromycin, and azithromycin) are used to treat common bacterial infections and are considered alternatives for patients with penicillin allergy.

Read more about sleeping in pregnancy

    Was this information useful?

    Yes No