“Snoring while pregnant is linked to smaller babies,” reports The Daily Telegraph. There is also evidence that snoring can lead to an increased risk of a baby having to be delivered by caesarean section.

This news is based on the results of a US cohort study that questioned a group of women during their last trimester of pregnancy (weeks 29 and over).

The researchers asked whether the women “habitually” snored (snoring three to four nights per week or nearly every night), and then followed up their birth outcomes. It found that self-reported “habitual” snoring, in particular snoring before and during pregnancy, was associated with increased likelihood of having a baby small for gestational age. There was also an increased likelihood of caesarean delivery.

The researchers adjusted for a number of factors that could be responsible for any association seen (confounders), such as mother’s age. However, this study cannot show that snoring directly caused the poorer delivery outcomes, as there could be other confounding health or lifestyle factors that were not adjusted for.

The researchers speculate that snoring leads to increased levels of inflammation which could affect the placenta leading to low birthweight. But this hypothesis needs further investigation.

Overall, pregnant women who snore should not be overly concerned by this research that snoring is going to have a harmful effect on their baby. What is important though, is for pregnant women to be able to get adequate rest.

Though, as the researchers suggest, it may be useful for health professionals to ask about snoring symptoms, and if appropriate, recommend treatments.

Why do people snore?

Snoring is caused by the vibration of the soft tissue in the head and neck as a person breathes in.

The vibration can be amplified by a number of risk factors, leading to louder snoring. The factors include:

• Obesity
• Smoking
• Drinking alcohol before going to sleep

Read more about the causes of snoring.

Where did the story come from?

The study was carried out by researchers from the University of Michigan, US. It was funded by the Gene and Tubie Gilmore Fund for Sleep Research, the University of Michigan Institute for Clinical and Health Research and the US National Heart, Lung and Blood Institute.

The study was published in the peer-reviewed journal Sleep.

The results of the study were accurately reported in the media.

What kind of research was this?

This was a cohort study. It aimed to examine the impact of maternal snoring during pregnancy on key delivery outcomes.

These outcomes included mode of delivery (vaginal or via caesarean section) and birth centile. Birth centiles are a method of comparing birthweight to the rest of the population. For example, if birth centile was below the 10th centile, this means that for every 100 infants less than 10 have lower birthweights. In this study, centiles were customised to take into account factors including maternal height, weight, and ethnicity and the infant’s gender and gestational age at birth.

A cohort study is the ideal study design to investigate this question. However, while the researchers adjusted for a number of factors that could be responsible for any association seen (confounders), this study cannot show that snoring caused poorer delivery outcomes. There could be other confounders that were not adjusted for.

What did the research involve?

The researchers recruited 1,673 pregnant women in their third trimester of pregnancy (this study included those of 28 weeks’ gestation or more) who attended antenatal clinics within the University of Michigan.

The women were asked whether they habitually snored or whether they had stopped breathing or gasped for air at night. Habitual snoring was defined as snoring either “three to four times per week” or “almost every day”. If women reported habitual snoring, they were asked when they started snoring. If women snored both before and during pregnancy, their snoring was classified as chronic. If snoring only started during pregnancy, the snoring was classified as pregnancy-onset snoring.

Delivery outcomes were obtained from medical records. The primary study outcomes were birth centile, mode of delivery (vaginal or caesarean section), cord blood gases (which helps determine whether the baby has been deprived of oxygen) and newborn transfer (whether the baby had to go into intensive care).

The researchers looked at whether snoring was associated with poorer delivery outcomes. The researchers tried to control their analyses for important potential confounders, such as mother’s age, body mass index (BMI), pre-eclampsia, number of previous pregnancies and maternal smoking.

What were the basic results?

Of the 1,673 women, 35% reported habitual snoring (26% who had started snoring in pregnancy, and 9% who were “chronic” snorers).

Chronic snoring was associated with:

• Having a small for gestational age baby (birthweight less than the 10th birth centile) (odds ratio [OR] 1.65, 95% confidence interval [CI] 1.02 to 2.66).
• Having a caesarean section (planned, not emergency) (OR 2.25, 95% CO 1.22 to 4.18)

Pregnancy onset snoring was associated with:

• Having an emergency caesarean delivery (OR 1.68, 95% CO 1.22 to 2.30)

How did the researchers interpret the results?

The researchers concluded that: “Maternal snoring during pregnancy is a risk factor for adverse delivery outcomes including caesarean delivery and small-for-gestational age. Screening pregnant women for symptoms of SDB [sleep disorders breathing] may provide an early opportunity to identify women at risk of poor delivery outcomes.”

Conclusion

This large cohort study has found that self-reported snoring during the last trimester of pregnancy – and in particular chronic snoring – is associated with having a small for gestational age baby as well as a caesarean delivery.

A cohort study is the ideal study design to investigate this question, and the researchers have attempted to adjust for a number of important potential confounding factors that could be responsible for any association seen, such as maternal age, BMI and smoking status.

However, this study cannot show that snoring directly caused the poorer delivery outcomes, as there could be other health or lifestyle factors not adjusted for that are involved in the relationship.

In addition, in this study snoring was self-reported. It is possible that other women snored who were not aware of it (though the vast majority of women had bed partners, and only 2% of partners complained about snoring when women reported not snoring).

This study cannot tell us whether, if there is a direct link between snoring and poor delivery outcomes, by what biological mechanism this may be.

The researchers speculate that snoring leads to increase levels of inflammation which could affect the placenta leading to low birthweight. But this hypothesis needs further investigation.

Overall, pregnant women who snore should not be overly concerned by this research that this is going to have a harmful effect on their baby.

The research does raise the possibility that it may be helpful for health professionals to ask whether an expectant mother is a snoring, and if so, offer advice or treatment.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.

Summary

“Snoring while pregnant is linked to smaller babies,” reports The Daily Telegraph. There is also evidence that snoring can lead to an increased risk of a baby having to be delivered by caesarean section.

Links to Headlines

• Snoring while pregnant linked to smaller babies. The Daily Telegraph, October 31 2013
• Pregnant women who snore ‘have smaller babies’. The Independent, October 31 2013
• Pregnant women who snore give birth to smaller babies, study reveals. Daily Mirror, October 31 2013

Links to Science

• O’Brien L, Bullough AS, Owusu JT, et al. Snoring During Pregnancy and Delivery Outcomes: A Cohort Study. Sleep. Published online October 2013

“Daily iron in pregnancy reduces small baby risk,” BBC News reports, with a similar story in the Daily Express.

The news stories follow a major review of the best available evidence on the link between use of iron supplements during pregnancy, and pregnancy and birth outcomes.

The pooled results suggest that, compared with no supplements, taking iron supplements increases the mother’s haemoglobin levels, and halves the risk of the mother becoming anaemic during pregnancy.

Supplements also resulted in the baby being on average 41.2g heavier at birth and reduced the risk of low birthweight by 19%. The findings showed a dose-response relationship, with higher doses being associated with lower risk of maternal anaemia and lower risk of low birthweight.

Different Types of Anaemia

There are several different kinds of anaemia, with iron-deficiency anaemia being the commonest. However, anaemia can also be caused by vitamin B12 or folate deficiency.

Overall, this offers evidence to back iron supplementation during pregnancy. However, this review focussed on low, middle and high income countries. Women do need increased iron during pregnancy, but in the UK, should be able to get all the iron they need in their diet (such as from leafy vegetables).

Currently, iron supplements are recommended if pregnancy blood tests show that the mother is anaemic. They are not routinely offered to all pregnant women due to the potential for side effects. Folic acid supplements are, however, recommended while trying to conceive and during the first 12 weeks of pregnancy.

Where did the story come from?

The study was carried out by researchers from Harvard School of Public Health, Harvard Medical School and Imperial College, London. Funding was provided by the Bill and Melinda Gates Foundation. Additional support came from the Saving Brains Program, Grand Challenges Canada Grant.

The study was published in the peer-reviewed, British Medical Journal.

The news stories provide a representative view of the findings.

What kind of research was this?

This was a systematic review and meta-analysis. It pooled the results from randomised controlled trials and observational cohort studies that examined the relationship between use of iron supplements during pregnancy, and pregnancy and birth outcomes.

The researchers say that iron deficiency is the most common cause of anaemia during pregnancy worldwide. Because of this, the World Health Organization recommends the use of antenatal iron supplements in low and middle income countries, and it is also recommended in some high income countries.

Observational studies are said to have found suggested links between iron deficiency anaemia and premature birth, and clinical trials have given inconclusive results on the link between iron levels and birth outcomes.

This review aimed to address this question by identifying all observational studies and clinical trials investigating the issue, and pooling the results in meta-analysis to see whether there is a link between use of iron supplements during pregnancy and haemoglobin levels in the mother and birth outcomes. A systematic review is the best way to examine the current evidence related to this issue.

What did the research involve?

The researchers conducted a search across medical databases up to May 2012, including randomised controlled trials in pregnant women investigating the use of daily oral iron or iron and folic acid supplements compared with inactive placebo pill or no treatment.

They excluded trials that investigated multiple vitamins or minerals, or in women with significant illnesses (such as mothers infected with HIV). Trials were required to have examined maternal outcomes such as anaemia (defined as haemoglobin <110g/l) and iron deficiency (defined as serum ferritin <12 micrograms/l), and birth outcomes, such as premature birth, birthweight and infant death around the time of birth.

Their search also included observational cohort studies that prospectively followed the association between baseline anaemia and birth outcomes.

The researchers assessed the quality of included studies, and pooled their results where possible, taking into account the differences between the findings of the individual studies (heterogeneity).

What were the basic results?

Findings from clinical trials

The researchers identified 48 randomised controlled trials (27 in high income countries and 21 in low/middle income) which included a total of 17,793 pregnant women.

Most of these trials (34) compared the use of daily iron supplements to no iron or placebo. Others compared iron in combination with folic acid to no treatment, or iron in combination with other micronutrients to the micronutrients without iron.

The dose of iron in the majority of included trials ranged from 10mg to 240mg daily. Duration of supplementation varied from seven or eight weeks through to 30 weeks during pregnancy.

When they pooled the results of 36 of these trials, they found that iron supplements increased the mother’s haemoglobin concentration by an average difference of 4.59g/l compared with the control groups (95% confidence interval (CI) 3.72 to 5.46g/l). Heterogeneity between these trials was non-significant, suggesting that all trials gave broadly similar results. When they pooled the results of 19 trials they found that iron supplements (with or without folic acid) significantly reduced the mother’s risk of anaemia by 50% (relative risk (RR) 0.50, 95% CI 0.42 to 0.59).

However, there were significant differences (heterogeneity) between these trials, suggesting that the results of the individual trials were quite different from each other for this outcome. When the researchers pooled trials looking at other markers of anaemia, eight trials also found that iron supplements (with or without folic acid) reduced risk of maternal iron deficiency by 41% (RR 0.59, 95% CI 0.46 to 0.79), and six trials found they reduced risk of iron deficiency anaemia by 60% (RR 0.40, 95% CI 0.26 to 0.60).

The researchers estimated that for every 10mg increase in iron intake per day, up to 66mg/day, the risk of maternal anaemia decreased by 12% (RR 0.88, 95% CI 0.84 to 0.92).

Forty-four cohort studies were included (22 from high income countries), including 1,851,682 women. Anaemia was said to be variably defined by these studies, and measured at different times during pregnancy.

The pooled results of six of these observational studies found that anaemia during the first or second trimester of pregnancy was associated with a 29% higher risk of low birthweight baby (odds ratio (OR) 1.29, 1.09 to 1.53), but no significant association when considering only studies from high-income countries (OR 1.21, 95% CI 0.95 to 1.53).

Seven studies found that anaemia during the first or second trimester was associated with a 21% higher likelihood of premature birth (OR 1.21, 95% CI 1.13 to 1.30). The association between third trimester anaemia and premature birth was non-significant (OR 1.20, 95% CI 0.80 to 1.79), however, the results for these third trimester studies varied considerably.

How did the researchers interpret the results?

The researchers conclude that daily iron supplements during pregnancy increase maternal haemoglobin and substantially improve birthweight in a dose-response fashion, leading to a reduced risk of a low birthweight baby.

Conclusion

This was a well-conducted systematic review and meta-analysis. It looked at the findings from 48 randomised controlled trials, including almost 18,000 women, that reviewed the effects of iron supplementation during pregnancy (with or without folic acid) upon maternal anaemia during pregnancy and birth outcomes.

The pooled results of the trials provide good evidence that iron supplements increase the mother’s haemoglobin levels (by an average 4.59g/l compared with the control groups) and halve the risk of the mother becoming anaemic during late pregnancy or around the time of birth. Supplements also resulted in the baby being on average 41.2g heavier at birth and decreased the risk of the baby being of low birthweight by 19%.

The findings showed a dose-response relationship, with higher doses being associated with lower risk of maternal anaemia and lower risk of low birthweight.

There were, however, differences between the results of individual trials, possibly a result of the trials’ differing methods and included populations, meaning the risk reductions calculated may not be precise.

Evidence from observational cohort studies found an association between iron supplementation and lower risk of premature birth. However, the randomised control trials do not support this observation.

Randomised trials are the better study design to test the effect of an intervention, as cohort studies may be influenced by other confounding factors. This is because, for example, women in cohorts are choosing to take supplements, and their choice may be associated with other improved health and lifestyle factors, such as better diet, that improve outcomes for mother and baby.

The researchers acknowledge a further limitation of their review: that they lacked data for some outcomes (such as stillbirths, newborn illnesses and early death).

Overall, the study provides evidence to support the use of iron supplementation during pregnancy. However, the results of this review covers low, middle and high countries. It is true that women need increased iron during pregnancy, but woman should be able to get all the iron they need through their dietary sources (such as from leafy vegetables).

Current UK guidance recommends that iron supplements are considered if pregnancy blood tests show that the mother is anaemic. But iron supplements are not offered routinely to all pregnant women due to the potential for side effects. Folic acid supplements are, however, recommended while trying to conceive and during the first 12 weeks of pregnancy.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.

Summary

“Daily iron in pregnancy reduces small baby risk,” BBC News reports, with a similar story in the Daily Express. The news stories follow a major review of the best available evidence on the link between…

Links to Headlines

• Daily iron pill during pregnancy ‘leads to healthier babies’. Daily Express. June 21 2013
• Daily iron in pregnancy ‘reduces small baby risk’. BBC News.

Links to Science

• Haider BA, et al. Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis. BMJ. Published online June 21 2013

From www.nhs.uk