Preterm births in Iceland 1997-2016: Preterm birth rates by gestational age groups and type of preterm birth

Prevalence of preterm birth in Scandinavian countries: a systematic review and meta-analysis

OBJECTIVES

As welfare societies, Scandinavian countries share characteristics of equality related to healthcare access, gender, and social services. However, cultural and lifestyle variations create country-specific health differences. This meta-analysis assessed the prevalence of preterm birth (PTB) and its categories in Scandinavian countries.

METHODS

A systematic search in key databases of literature published between 1990 and 2021 identified studies of the prevalence of PTB and its categories. Following the use of the Freeman-Tukey double arcsine transformation, a meta-analysis of weighted data was performed using the random-effects model and meta-prop method.

RESULTS

We identified 109 observational studies that involved 86,420,188 live births. The overall pooled prevalence (PP) of PTB was 5.3% (PP = 5.3%, 95% confidence interval [CI] 5.1%, 5.5%). The highest prevalence was in Norway (PP = 6.2%, 95% CI 5.3%, 7.0%), followed by Sweden (PP = 5.3%, 95% CI 5.1%, 5.4%), Denmark (PP = 5.2%, 95% CI 4.9%, 5.3%), and Iceland (PP = 5.0%, 95% CI 4.4%, 5.7%). Finland had the lowest PTB rate (PP = 4.9%, 95% CI 4.7%, 5.1%).

CONCLUSIONS

The overall PP of PTB was 5.3%, with small variations among countries (4.9%-6.2%). The highest and lowest PPs of PTB were in Norway and Finland, respectively.

Twin birth rates and obstetric interventions in Iceland: A nationwide study from 1997 to 2018

OBJECTIVE

Twin pregnancies are associated with increased antepartum and intrapartum risks. Limited multiple embryo transfers are associated with decreased twin birth rates. We aimed to study the effect of 2009 Icelandic regulations on twin birth rates and examine obstetric intervention rates for twin births during the study period.

METHODS

The study included all births (N = 94 028) in Iceland during 1997-2018. Twin birth rates and obstetric intervention rates were compared over birth year periods using modified Poisson regression adjusted for confounders.

RESULTS

An observed decrease in the twin birth rate trend was most notable from 2006 until 2009. Twin birth decreased in 2009-2013 (prevalence ratio [PR] 0.74, 95% confidence interval [CI] 0.64-0.86) and in 2014-2018 (PR 0.74, 95% CI 0.64-0.86) compared with 1997-2002. This decrease was only evident for women aged 30+ years in stratified analysis. Induction of labor rates increased from 26% in 1997-2002 to 44% in 2014-2018 (adjusted rate ratio [ARR] 2.10, 95% CI 1.72-2.57) whereas elective cesarean section (ARR 0.80, 95% CI 0.59-1.07) and urgent cesarean section (ARR 0.79, 95% CI 0.63-1.00) rates appeared to decline.

CONCLUSION

Twin births decreased during the study period. International guidelines published before the Icelandic regulations may have affected twin birth rates in Iceland. Induction of labor rates for twins increased while cesarean section rates decreased.

Trimester-specific associations of maternal dietary patterns with preterm birth: China Medical University birth cohort study

The trimester-specific associations of maternal dietary patterns with preterm birth (PTB) are unclear. In a prospective prebirth cohort study, we aimed to examine the critical time window of maternal prenatal dietary patterns and the risk of PTB. We assessed prenatal dietary intake among 1500 pregnant women with validated food frequency questionnaires during the 1st, 2nd and 3rd trimester, respectively. We used logistic regression models and generalized estimating equation models to examine the trimester-specific associations and longitudinal associations between maternal dietary patterns in relation to risk of PTB and PTB subtypes. The incidence rate of PTB was 11.9% (179 out of 1500 pregnant women) in the present study. We observed that maternal adherence to a fish-seafood pattern in the 1st trimester was associated with higher risk of PTB [tertile 3 (T3) vs. tertile 1 (T1): OR = 2.29, 95% CI: 1.32-3.96] and iatrogenic preterm birth (IPTB) (T3 vs. T1: OR = 2.26, 95% CI: 1.21-4.20), while a fish-seafood pattern in the 2nd trimester was associated with lower risk of PTB (T3 vs. T1: OR = 0.49, 95% CI: 0.25-0.93). Maternal adherence to a dairy-egg pattern in the 2nd or 3rd trimester was associated with higher risks of PTB and IPTB. No dietary patterns were associated with spontaneous preterm birth. Our findings provide new evidence that specific dietary patterns during different trimesters may have different and even inverse health effects on pregnant women. This supports the necessity of guiding the maternal diet according to different periods of pregnancy to prevent PTB.

Metabonomics profile analysis in inflammation-induced preterm birth and the potential role of metabolites in regulating premature cervical ripening

BACKGROUND

Preterm birth (PTB) is the primary cause of infant morbidity and mortality. Moreover, previous studies have established that PTB is related to premature cervical ripening. However, the underlying mechanism remains to be elucidated. This study sought to identify differentially expressed metabolites and investigate their potential biological functions in PTB.

METHODS

Pregnant C57BL/6 J mice were treated with either LPS or normal saline and cervical alterations before labor were detected by staining. Metabolic profiles in the plasma of PTB and control mice were examined through non-targeted metabonomics analyses, quantitative polymerase chain reaction and immunofluorescence staining were performed on human cervical smooth cells.

RESULTS

The study demonstrated that the mRNA and protein levels of α-SMA, SM-22, and calponin in cervical smooth muscle cells of PTB mice were lower while OR was higher at both mRNA and protein levels compared to the CTL group. A total of 181 differentially expressed metabolites were analyzed, among them, 96 were upregulated, while 85 were downregulated in the PTB group. Differentially expressed metabolites may play a role in STAT3, RhoA, mTOR, TGF-β, and NK-κB signaling pathways. Furthermore, when treated with taurine, the levels of α-SMA and SM-22 in human cervical smooth muscle cells were elevated, whereas that of connexin-43 was decreased.

CONCLUSION

Our study highlighted the changes of metabolites in the peripheral blood changed prior to PTB and revealed that these differentially expressed metabolites might participate in the development of premature cervical ripening. Taurine was identified as an important metabolite may modulate human cervical smooth muscle cells. Our study provided new insights into the mechanism underlying premature cervical ripening in PTB.

Neonatal pain, thalamic development and sensory processing behaviour in children born very preterm

BACKGROUND

Altered sensory processing is commonly reported in children born very preterm (≤32 weeks' gestational age [GA]). The immature nervous system, particularly the development of connections from the thalamus to the cortex, may show enhanced vulnerability to excessive sensory stimulation, and may contribute to altered sensory processing. Our objective was to determine whether sensory processing assessed at preschool-aged in children born very preterm was predicted by neonatal procedural pain and thalamic development.

METHODS

In a prospective longitudinal cohort study, N = 140 very preterm infants (median GA at birth 28 weeks) underwent MRI early-in-life and again at term-equivalent age. Children returned for assessment at 4.5 years. Parents reported on child sensory processing behaviors on the Short Sensory Profile. General linear models were used to assess factors associated with sensory processing behaviors, adjusting for clinical and demographic factors.

RESULTS

Among extremely preterm neonates (born 24-28 weeks' GA), but not very-preterm neonates (29-32 weeks' GA), more invasive procedures were associated with poorer sensory processing (B = -0.09, 95%CI [-0.17, -0.01] p = 0.03). In the overall cohort, fewer sensory processing problems were associated with greater thalamic growth between birth and term-equivalent age (B = 0.3, 95%CI [0.11, 0.42], p < 0.001). Extremely preterm neonates exposed to a high number of skin-breaking procedures who exhibited slower neonatal thalamic growth displayed the highest sensory processing problems (B = -26.2, 95%CI [-45.96, -6.38], p = 0.01).

CONCLUSION

Early exposure to pain and related alterations in the developing thalamus may be a key factor underlying later sensory problems in children born extremely preterm.

Trends in cesarean birth rates in Iceland over a 19-year period

BACKGROUND

Cesarean birth (CB) rates have increased in high-resource countries during the past two decades, yet it is not known whether CB rates have changed according to maternal age and/or gestational age.

METHODS

All singleton live births in Iceland between 1997 and 2015 were identified from the Icelandic Medical Birth Registry (80 130). Rates of cesarean births (intrapartum and prelabor) were calculated overall and separately for maternal age groups and gestational age groups and by parity. Logit binomial regression was used to calculate odds ratios (ORs) and confidence intervals (CIs) for annual change in cesarean birth rates adjusted for maternal characteristics and clinical indication groups.

RESULTS

The overall CB rate was 15.7% in 1997 and 15.8% in 2015; the CB rate did not change significantly during the study period. The overall CB rate for early-term deliveries (37-38 weeks) decreased for multiparas (annual aOR = 0.99 [95% CI = 0.98-0.99]), and the preterm (<37 weeks) prelabor cesarean rate increased significantly (1.11 [1.09-1.14]) for both primiparas and multiparas. For multiparas only, the intrapartum CB rate decreased (0.97 [0.97-0.98]), whereas the prelabor CB rate increased, predominantly for women aged over 35 years (1.03 [1.02-1.04]). Adjustment for clinical indication groups did not change these results.

CONCLUSIONS

Findings indicate a rise in prelabor cesarean for preterm births and women aged over 35 years (multiparas only). As adjustment for clinical indications did not affect these results, changes in obstetric practice are more likely to have affected these rate changes rather than changes in clinical indications.

Maternal Coronary Heart Disease, Stroke, and Mortality Within 1, 3, and 5 Years of Delivery Among Women With Hypertensive Disorders of Pregnancy and Pre-Pregnancy Hypertension

Background Pre-pregnancy hypertension and hypertensive disorders of pregnancy (HDP; preeclampsia, eclampsia, gestational hypertension) are major health risks for maternal morbidity and mortality. However, it is unknown if racial/ethnic differences exist. We aimed to determine the impact of HDP and pre-pregnancy hypertension on maternal coronary heart disease, stroke, and mortality risk ≤1, 3, and 5 years post-delivery and by race/ethnicity ≤5 years. Methods and Results This retrospective cohort study included women aged 12 to 49 years with a live, singleton birth between 2004 to 2016 (n=254 491 non-Hispanic White; n=137 784 non-Hispanic Black; n=41 155 Hispanic). Birth and death certificates and International Classification of Diseases, Ninth and Tenth Revision, Clinical Modification (ICD-9-CM and ICD-10-CM) diagnosis codes in hospitalization/emergency department visit data defined HDP, pre-pregnancy hypertension, incident coronary heart disease and stroke, and all-cause mortality. During at least 1 pregnancy of the 433 430 women, 2.3% had pre-pregnancy hypertension with superimposed HDP, 15.7% had no pre-pregnancy hypertension with HDP, and 0.4% had pre-pregnancy hypertension without superimposed HDP, whereas 81.6% had neither condition. Maternal deaths from coronary heart disease, stroke, and all causes totaled 2136. Within 5 years of delivery, pre-pregnancy hypertension, and HDP were associated with all-cause mortality (hazard ratio [HR], 2.21; 95% CI, 1.61-3.03), incident coronary heart disease (HR, 3.79; 95% CI, 3.09-4.65), and incident stroke (HR, 3.10; 95% CI, 2.09-4.60). HDP alone was related to all outcomes. Race/ethnic differences were observed for non-Hispanic Black and non-Hispanic White women, respectively, in the associations of pre-pregnancy hypertension and HDP with all-cause mortality within 5 years of delivery (HR, 2.34 [95% CI, 1.58-3.47]; HR, 2.11 [95% CI, 1.23-3.65]; P interaction=0.001). Conclusions Maternal cardiovascular outcomes including mortality were increased ≤5 years post-delivery in HDP, pre-pregnancy hypertension, or pre-pregnancy hypertension with superimposed HDP. The race/ethnic interaction for all-cause mortality ≤5 years of delivery warrants further research.