List of Abbreviations
Chapter 3 Systematic review and meta-analysis 3.1 Introduction 3.1 Introduction
3.3.2.2 Measured birth outcomes
3.3.2.2.1 Neonatal pregnancy outcomes
Foetal growth was studied by studies included in the review using two different though related concepts: small for gestational age (SGA) being examined in six studies and low birth weight (LBW) in four. Newborn health and well-being were measured in three studies using Apgar scores and by admission to the neonatal intensive care unit (NICU) in two.
SGA was defined by Franklin et al. (2000) as a birth weight below 2 standard deviations of the median value in the Sweden infant weight reference charts; whilst it was defined by Howe et al. (2015), Ko et al. (2013), Bourjeily et al. (2010) and Abeysena et al. (2009) as simply a birth weight <10th percentile after adjusting for foetal sex and gestationalage at birth. O'Brien et al. (2013) further scaled the birth weight to maternal height, weight, ethnic origin, and parity (essentially adjusting birth weight by each of these preceding maternal covariates). Low birth weight (LBW) was examined by the studies authored by Sharma et al. (2016), Owusu et al. (2013), Chen et al. (2012) and Abeysena et al. (2010). In all of these studies LBW was defined as a birth weight below 2500g as measured immediately after birth without adjusting for gestational age at birth or the sex of the newborn. The Apgar scores used were those measured immediately after birth (Bourjeily et al., 2010) and those measured 5 minutes thereafter (Sharma et al., 2016, Chen et al., 2012, Bourjeily et al., 2010). These two measurements were studied in relation to sleep using a value of ≥7 as the reference cut-off score.
NICU admission was reported regardless of the reason for admission or the length of stay, though only in two of the studies reviewed (Reutrakul et al., 2011, Louis et al., 2010).
Finally, fatal foetal outcomes were assessed using reports of miscarriage and stillbirth; miscarriage being defined by Samaraweera and Abeysena (2010) as partial or full expulsion of the foetus during the first 28 weeks of gestation.
Gordon et al. (2015), Owusu et al. (2013) and Stacey et al. (2011) examined the association between stillbirth and several unfavourable sleep events. Stacey et al.
(2011) defined stillbirth as the birth of a baby that had died in utero during the antenatal or intrapartum periods during/or after 28 weeks gestation, and did not suffer from congenital anomalies. In contrast, Gordon et al. (2015) included only those neonatal deaths that occurred during/or after 32 weeks gestation.
Since stillbirth and miscarriage are both extremely traumatic to mothers, a few of the studies explicitly excluded women with histories of these phenomena (Champagne et al., 2009).
3.3.2.2.2 Maternal pregnancy outcomes
The following maternal pregnancy outcomes were examined in relation to sleep by studies included in the review: gestational diabetes (GDM), pregnancy-induced hypertension (PIH), pre-eclampsia (PE), preterm delivery, and caesarean delivery (Table 3-10 and Table 3-11).
Eight references studied GDM as the outcome of interest, diagnosed using the 100g OGTT test. However, not all of these studies reported their GDM criteria (Table 3-10). Indeed, one study (Wang et al. 2017) used a 75g OGTT test to diagnose GDM in their study, whilst Herring et al. (2014) used a 50g non-fasting OGTT to diagnose hyperglycaemia rather than GDM.
Preterm delivery was defined as delivery before 37 weeks of gestation and was examined by 4 separate studies.
As for complications with delivery, the risk of elective and/or emergency caesarean delivery was examined in comparison to spontaneous or assisted vaginal delivery.
Emergency caesarean delivery was examined separately (i.e. not in conjunction with elective caesarean delivery) in just one reference (Bourjeily et al., 2013).
Elective caesareans are important to examine separately since these may be likely to be decisions taken due to causes that occurred prior to the measurement of sleep – such as uterine abnormalities or a previous history of caesarean delivery.
In addition, elective caesarean delivery may be secondary to causes that follow sleep measurement (such as excessive foetal growth or breech position).
However, examining caesarean deliveries alongside emergency caesareans would not necessarily cause confounding bias, but it might cause measurement error or mediation bias.
Pregnancy-induced hypertension (also known as gestational hypertension), which is a key component of pre-eclampsia, was examined in relation to sleep in a total of 12 different studies (Table 3-10), 5 of which distinguished PIH from PE (Ko et al., 2013, Owusu et al., 2013, Ugur et al., 2012, Louis et al., 2012, Williams et al., 2010). In these studies, pre-eclampsia was defined as elevated blood pressure after 20 weeks of gestation with a diastolic reading >90 mmHg or a systolic reading
>140 mmHg plus proteinuria of >300 mg/24 hr. In contrast, PIH was defined as elevated blood pressure after 20 weeks of gestation with or without proteinuria.
.
Table 3-10 Summary of pregnancy outcomes examined by studies included in the review.
Reference Used definition Descriptive statistics
Small for gestational age Retrospective
longitudinal
(Bourjeily et al., 2010) Birth weight “<10th percentile for gestational age” Not reported (Franklin et al., 2000) “Birth weight below two standards deviation in the
Sweden infant weight charts”
Total participants=502
7% of 113 habitual snorers gave a birth to SGA infant
2.6% of 389 non- habitual snorers gave a birth for SGA (p<0.05 Prospective
longitudinal study
(Abeysena et al., 2009) Birth weight < 10th percentile adjusted for maternal height, feeding requirement, foetal sex, GA, ethnicity and maternal weight
Mean birth weight= 2946 g
(Howe et al., 2015) Birth weight “<10th percentile for gestational age” Total participants=633
Rate of SGA was 8.85% (n=56)
Rate of SGA in mother identifies as Māori (N=194) was 6.7%
(n=13)
Rate of SGA in mother identifies as non-Māori (N=439) was 9.8%
(n=43) (Ko et al., 2013) “<10th percentile adjusting for foetal sex and
gestational age”
17 participants of 276 total participants (6.16%) give a birth to SGA neonates
(O'Brien et al., 2013) Birth weight < 10th centile adjusted for maternal height, maternal weight, ethnic origin, parity, infant sex, gestational age
Birth weight < 10th centile =12.5% of total 1673 participants
Low birth weight Retrospective longitudinal study
(Owusu et al., 2013) Birth weight< 2500 g at birth Total participants=234
6 out of 53 snorers had low birth babies (11.3%)
21 out of 167 non-snorers had low birth weight babies (12.6%) : Prospective
longitudinal study
(Abeysena et al., 2010) Birth weight< 2500 g at birth Mean= 2946± 473 g
87 LBW babies (11.8%) from 885 babies (Chen et al., 2012) Birth weight< 2500 g at birth Mean birth weight
Women with OSA= 306 (SD=584) g Women without OSA=3147(SD=418) g
233 women from the 4746 (4.91%) had LBW babies (Sharma et al., 2016) Birth weight< 2500 g at birth Total participants= 273
Rate of LBW was 31.14 % (n=85) Apgar score
Retrospective longitudinal study
(Bourjeily et al., 2010) 1-min. and 5-min. low Apgar scores (<7) Not reported
Reference Used definition Descriptive statistics Prospective
longitudinal study
(Chen et al., 2012) 5-min. low Apgar scores (<7) Total participants=4786 Women with OSA=10 (1.3%) Women without OSA= 5(0.1%) P<0.001
(Sharma et al., 2016) 5-min. low Apgar scores (<7) Not reported NICU admission
Prospective longitudinal study
(Reutrakul et al., 2011) Not reported Not reported
(Louis et al., 2012) Not reported 12 (46.1%) women with OSA reported NICU admission
24 (17.8%) women without OSA reported NICU admission Still birth and miscarriage
Retrospective longitudinal studies
(Owusu et al., 2013) Not reported 2 out of 53 snorers had a still birth delivery (3.8%) 7 out of 53 non –snorers had a still birth delivery Case control
study
(Samaraweera and Abeysena, 2010)
“partial or full expulsion of the foetus during the first
28 weeks of gestation” Women with miscarriage 230
Women without miscarriage 501 Amongst women with miscarriage:
1st trimester miscarriage= 91/230 women (39.5%) 2nd trimester miscarriage= 139/230 women (60.4%) (Stacey et al., 2011) “Stillbirth was defined as the birth
of a baby that died in utero during the antenatal or intrapartum periods” GA= ≥ 28 week
Pregnant women experienced late still birth = 215 Prevalence of still birth = 3.09/1000 births
The absolute risk of late stillbirth = 3.09/1000 95% CI= 2.70 to 3.53/1000 (Gordon et al., 2015) Late still birth during or after 32 weeks of gestation Women with still birth =103
Women with viable birth= 192 Gestational diabetes
Prospective longitudinal study
(Qiu et al., 2010) If one of the following results was positive using 100 grams, 3-hour OGTT
• fasting ≥ 95 mg/dl
• 1-hour ≥ 180 mg/dl
• 2-hour ≥ 155 mg/dl
• 3-hour ≥140 mg/dl.
68 /1290 women (5.3%) developed GDM
(Reutrakul et al., 2011) The test was done using 100-g OGTT But no cut off point was reported
26 women (15%) had GDM (Facco et al., 2010) The test was done using 100-g OGTT
But no cut off point was reported
9 out of the 88 women With short sleep duration (10.2%) and 1 out of the 94 women Without short sleep duration (1.1%) were diagnosed with GDM
P<0.008
Reference Used definition Descriptive statistics
(Chen et al., 2012) Not reported Women with OSA=37 (4.7%)
Women without OSA=130 (3.3%) P<0.053
(Herring et al., 2014) Hyperglycemia was identified if the blood glucose level was ≥130 mg/dL using 50-g non-fasting OGTT with
1 hour sample
From the 63 participants 7 women (11%) were classified with hyperglycemia
(O’Brien et al., 2012) Not reported 19%women from 584 women with snoring had GDM
15 %women from the1128 non- snorer women had GDM (Reutrakul et al., 2013) Using 100-g OGTT
Two abnormal readings
Using 1- hour glucose tolerance test with 50 g OGTT Blood glucose=≤ 140 mg/dl
Blood glucose =≥ 200 mg/dl
Pregnant women with GDM= 15 Pregnant women without GDM= 15
(Sharma et al., 2016) American Diabetes Association criteria Total participants= 273
Rate of women diagnosed of GDM= 14.65 % (n=40) (Wang et al., 2017) Using 75-g OGTT
GDM was diagnosed if one of the following Fasting glucose ≥ 5.1 mmol/l
1-h plasma glucose ≥ 10.0 mmol/l 2-h plasma glucose ≥ 8.5 mmol/l
7.3% (n=919) women had gestational diabetes
Retrospective longitudinal
(Bourjeily et al., 2013) American Diabetes Association criteria 94 (10%) women had GDM
(Bourjeily et al., 2010) Not reported 98 (9.8%) of women had GDM
Mode of delivery Prospective longitudinal study
(Lee and Gay, 2004) Both Elective and emergency caesarean General vaginal birth= 62%
Assisted vaginal birth=17%
Caesarean section=21%
(O'Brien et al., 2013) Emergency caesarean or Elective caesarean
Emergency CS= 19.4%
Elective CS= 18.2%
(Chen et al., 2012) Both Elective and emergency caesarean Women with OSA=399 (50.4%) Women without OSA=1475(37.3%) P<0.01
(Ko et al., 2013) Both Elective and emergency caesarean From 89 women with OSA 32 had caesarean delivery (36%) From187 women without OSA 42 (22.5%) caesarean delivery (Louis et al., 2012) Both Elective and emergency caesarean Total Caesarean delivery= 64 women 38%
Elective caesarean=40%
(Sharma et al., 2016) Both Elective and emergency caesarean Total participants= 273
Rate of CS was 28.57 % (n=78) Retrospective
longitudinal
(Bourjeily et al., 2013) Elective caesarean 498 (53%) women had vaginal delivery 305 (32.5%) women had
Caesarean delivery
Reference Used definition Descriptive statistics
(Bourjeily et al., 2010) Emergency caesarean 5.4% had
Caesarean delivery Preterm delivery
Prospective longitudinal study
(Louis et al., 2012) Delivery before 37 weeks From the 89 women with OSA 5 (17.6%) had preterm delivery From the 187 women without OSA 26 (18.5 %) had preterm delivery
(Louis et al., 2010) Not defined From the 57 women with OSA 17 (29.8%) had preterm delivery From the 114 obese women11 (9.6 %) had preterm delivery From the 114 normal weight women 14 (12.3%) had preterm delivery
(Stinson and Lee, 2003) Not reported 50 participants had preterm delivery (13.9%) (Okun et al., 2011) Delivery before 37 weeks Preterm delivery= 15 (9.0%)
Term delivery= 151 (91%) (Na-rungsri et al., 2016) Delivery before 37 weeks and was divided into Total participants= 1345
Preterm delivery= 143 (10.63%) Term delivery= 1197(88.99%)
(Reutrakul et al., 2011) Not reported Not reported
(Strange et al., 2009) Not reported Total preterm birth= 14.6%
Retrospective longitudinal
(Bourjeily et al., 2010) Delivery before 37 weeks 12% women from 1000 participants had preterm delivery Case control (Kajeepeta et al., 2014) Spontaneous and not medically indicated delivery
that happened before 37 weeks and after 22 weeks of gestation
Women with preterm delivery =479 Women with term delivery =480 Pre-eclampsia
Prospective longitudinal
(Williams et al., 2010) Not reported Not reported
(O'Brien et al., 2012) Not reported 12.9% from 584 snorers had PE
8.2% from 1128 non-snorers had PE (Ko et al., 2013) Systolic BP>140 mmHg or diastolic BP>90mmHg
Measured 2 times within 4-14 days apart plus protein urea >300gm/dl
3 of 89 women with OSA had PE 6 of 187 women without OSA had PE (Louis et al., 2012) New onset HTN (GA >20 week) in previously normal
women
(Franklin et al., 2000) pregnancy-induced hypertension with proteinuria ≥ 300 mg/24 hour
Total 26 cases of PE 10% in habitual snorer
4% in non habitual snorer p<0.05
Reference Used definition Descriptive statistics
(Owusu et al., 2013) Not reported 26 (11.8%)
12 out of 53 snorers developed PE (22.6%)
13 out of 167 non- snorers developed PE (7.8%), p<0.0065
(Chen et al., 2012) Not reported Women with OSA=11(1.4%)
Women without OSA=18 (0.5%) P<0.002
Gestational Hypertension Retrospective
longitudinal
(Bourjeily et al., 2010) 13% of 1000 participants had gestational hypertension
(Franklin et al., 2000) Not reported Total 40 cases of HTN
14 % in habitual snorer
6 % in non-habitual snorer p<0.01 (Perez-Chada et al.,
2007).
Blood pressure ≥140/90 mmHg, regardless of proteinuria.
Pregnancy-induced hypertensive disease occurred
in 42% snoring women compared to 27% of the women who had never snored (p<0.001)
(Reid et al., 2011) After 20 weeks of Gestation With or without proteinuria
422 out of 8651 deliveries between 2/2006 and 2/2008 were diagnosed with PIH
216 included in the study
(Chen et al., 2012) Not reported Women with OSA=53 (6.7%)
Women without OSA=85 (2.2%) P<0.001
Case control (Champagne et al., 2009)
(O'Brien et al., 2012) Not reported 9.8% of the 584 the snorers participants had PIH 8.2% the 584 the non-snorers participants had PIH (Sharma et al., 2016) (a systolic blood pressure >140 mm Hg or a diastolic
blood pressure >90 mm Hg)
The rate of women with PIH= 27.11% (n=74)
Table 3-11 Summary of the studies included in the review together with the (sleep-related) exposures and (pregnancy outcome-related) outcomes examined.
Sleep duration Sleep quality Sleep disturbance Day sleepiness Latency Sleep Position
NICU admission (Reutrakul et al.,
2011)
Sleep duration Sleep quality Sleep disturbance Day sleepiness Latency Sleep
Preterm delivery (Kajeepeta et al., 2014)