- Partners and collaborators: Action Medical Research
- To identify modifiable risk factors for late stillbirth amenable to public health campaigns.
- In particular to confirm/refute the novel findings regarding maternal sleep factors, including maternal sleep position, and risk of late stillbirth.
- To clarify the relationship between altered patterns of fetal movements and stillbirth.
- To explore the interaction between maternal sleep variables, infant factors (such as fetal growth restriction, reduced fetal movements) and late stillbirth risk.
Primary outcome: Late stillbirth (at/after 28 weeks gestation).
Study design: Case-control study.
Cases: Women with singleton pregnancies and late stillbirth (not due to congenital abnormality) recruited from obstetric units in the Midlands and the North of England.
Controls: Women with singleton ongoing pregnancies, recruited to match the gestation and hospital of birth of the stillbirths.
Methods: Interviewer-administered questionnaire which asks many questions regarding potential modifiable factors associated with stillbirth. Interviews will be conducted by trained midwives at a time arranged by the parents. Experience from Auckland found that women that the questions did not increase maternal anxiety, indeed many stillbirth mothers welcomed the opportunity to talk about their experience.
Sample size: There will be 2 controls per case. We will require approximately 290 women with late stillbirth and 580 controls to have power (80%) to detect a risk factor with an Odds Ratio (OR) of 1.5 and an interaction with OR of 2.5 with a significance level of 0.05. Assuming 30% non-participation rate we need to approach 415 eligible cases and 830 eligible controls (72% recruitment was achieved in the Auckland Stillbirth Study).
The death of a baby before birth is a tragedy for the family and wider community. Stillbirth remains far too common. In high-income countries, more than one in two hundred births result in a stillbirth . The stillbirth rate in the United Kingdom ranks 33rd out of 35 high-income countries, with little decrease in its rate over the last two decades . The Stillbirth and Neonatal Death Charity (Sands) and the Royal College of Obstetricians and Gynaecologists (RCOG) have called for more research, particularly into stillbirth prevention. Although there has been little reduction in stillbirths in the last two decades, this is not the case for sudden infant death syndrome. One reason for this was the identification of modifiable risk factors (eg infants sleeping on their front) that were amenable to intervention (the “back to sleep” campaign). Studies are needed to identify risk factors for stillbirth that may be amenable to similar interventions. Although there have been a number of studies that have examined risk factors for stillbirth, many have examined whole populations in retrospective studies that have not been able to explore risk factors relating to maternal lifestyle, personal habits and experiences in pregnancy. An alternative strategy is needed to evaluate modifiable factors that are amenable to public health campaigns; such factors include maternal sleep position and maternal perception of reduced fetal movements (RFM).
Around a third of an individual’s life is spent asleep and yet there has been little research on the potential impact of sleep practices on the developing baby. Previous studies have found a link between disordered breathing during sleep such as snoring and pregnancy complications such as pre-eclampsia and preterm birth . However, exploration of a potential link with stillbirth has been limited to a single report . There is a well-established relationship between maternal obesity and stillbirth risk , but the mechanisms underlying this association are not understood. Importantly, obesity is also associated with disordered breathing during sleep . Therefore, it is possible that sleep-disordered breathing is one of the mechanisms linking obesity and stillbirth risk. Maternal sleep position, specifically laying flat on the back is associated with sleep-disordered breathing . The impact of maternal position during sleep and risk of stillbirth was not examined before the Auckland Stillbirth Study.
The broad aim of the Auckland Stillbirth Study was to identify potentially modifiable risk factors for late stillbirth (≥28 weeks). We (TS, EM, LM) explored a range of factors relating to women’s health and behaviour during pregnancy, including general health, socioeconomic factors, diet, exercise, perception of fetal activity and maternal sleep practices . In the Auckland Stillbirth Study we hypothesised that sleep-disordered breathing and maternal supine sleep position would be associated with increased risk of late stillbirth. We also investigated the relationship between risk of late stillbirth and other sleep related practices, specifically; regular daytime sleep, duration of sleep, and getting up during the night. This study was conducted in Auckland, New Zealand between 2006 and 2009, when the prevalence of late stillbirth was 3.1 per 1,000 births. We found that maternal non-left position on going to sleep (on the presumed last night prior to stillbirth, or prior to interview) was associated with a two-fold increase in late stillbirth. The greatest effect was when the mother went to sleep on her back and intermediate when on the right. These findings remained significant after adjustment for other associations with stillbirth including maternal body mass index, age and cigarette smoking. In addition, we found that women who got up to the toilet once or less on the last night were more likely to experience a late stillbirth compared to women who got up more frequently. Women who regularly slept during the day in the last month of the pregnancy were also more likely to experience a late stillbirth compared to those who did not. In addition, the Auckland stillbirth study provided further evidence of the association between reduced fetal movements (RFM) and late stillbirth. Women noting RFM had a two-fold increased risk of stillbirth. In summary, the Auckland Stillbirth Study highlighted two areas, maternal sleep practices and perception of fetal activity which might be amenable to public health campaigns to reduce stillbirth.
Responses to the Auckland Stillbirth Study highlighted potential confounding factors including that women with fetal growth restriction may be more likely to sleep on their back as their bump is smaller, and recall of sleep position by mothers after stillbirth may be biased or inaccurate. The study proposed here will confirm or refute the link between late stillbirth and maternal sleep practices and RFM and whether these factors interact with each other. In so doing it will provide valuable data to determine whether an intervention study based on maternal sleep position and awareness of fetal movements could reduce stillbirth.
Dr Alexander Heazell Manchester
Dr Tomasina Stacey Leeds
Dr Bill Martin Birmingham
Dr Devender Roberts Liverpool
New Zealand Professor Ed Mitchell, Professor Lesley McCowan
Contact: Tomasina Stacey
Funding body: Action Medical Research £194,680